Blood Pressure
Content
Spacelabs Medical: BLOOD PRESSURE
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B L O O D P R E S S U R E And.ew R . Nara, M.D., Ph.D., F.A.C.C., F.C.C.R Assistant Professor of Medicine Medicine Case Western Reserve University Director, Cardiac Intensive Cardiac Intensive Care Unit Division of Cardiology Cleveland University Hospitals of Cleveland Cleveland Cleve land,, Ohio
Michael P . Burns, R.N., B.A., B.A., B B . S.N. Research Nurse Cardiology Division of Cardiology University Hospitals of Cleveland Cleveland Cleveland Cleve land,, Ohio
W . Gregory Downs, B.S.E. Research Biomedical Engineer Cardiology Division of Cardiology University Hospitals of Cleveland Cleveland Cleveland, Ohio
This book is part of the the SpaceLabsMedical Biophysical Measurement Book Series for biomedical an and d clinical professionals. The series is an educational service of SpaceLabs Medical, a leading provider of patient patient monitoring and clinical informatio information n system systems. s. © SpaceLabs Medical, Inc., 1993
First Printing, 1990 Second Printing, 1993 All rights reserved. No part part of of this book may may be reproduced by an any y means or transmitted, transmitted, or translated into a machine language without th the e written permission of th the e publisher.
All brands an and d product names are trademarks of the their ir respective owners. respective owners.
Published by SpaceLabs Medical, Inc., Redmond, Washington, U.S.A. the e United States. Printed in th
ISBN 0-9627449-0-5
Spacelabs Medical: BLOOD PRESSURE
T ABLE OF CONTENTS Page
INTRODUCTION
3.2 Fluid-filled Systems
tO ARTERIAL PRESSURE
PULSES
3
1.1 Anatomy and Physiology of the Circulatory Syst~ein the Heart 1.1.1 Anatomy of the 1.1.2 Arterial System 11.3 Venous System 1.2 Cardiac Cycle 1.2.1 Ventricular Cycle Ventricular Cycle 1.2,2 Atrial Cycle
3 3 7 9
11 13 17
1.3 Standard Pressure Definitions
19
2.0 PRESSURE
21
21
TRANSMISSION
2.1 Harmonic Analysis of Blood Blo od Pres Pressure sure Wa Wavefo veforms rms
2.2 Fundamentals of Hydrau Hyd rau lic licss 2.2.1 Laminar and Turbulent Flow 2.2.2 Poiseuffle’s Law
25 27 29
2.3 Vascular Impedance Concepts 2.3.1 Measurement (Calculation) 2.3.2 Physiological Importance
29 29 31
2.4 Mean Mean Blood Blood Pressure Transmission: DC Analogy
31
2.5 Systolic and Diastolic Pressure Pressure Tnrnsmission: AC Analogy 37 2.5.1 Damping of High Frequencies.. . .38 38 2.5.2 Tapered Tube Tapered Tube Effect 2.5.3 Frequency Dispersion 38 2.5.4 Pressure Wave Reflection 39
3.0 INVASIVE (DIRECT) MEASUREMENT TECHNIQUES
3.1 Pressure Mecisurement Sites of Clinical Clinical interest 3.1.1 Peripheral Arterial Pressure 3.1.2 Central Venous and Pulmonary Artery Pressures 3.1.3 Left Ventricular Left Ventricular and Aortic Pressures
41 41 43
48 52
3.2.1 Determination and Optimization of Frequency Response 3.2.2 Constant Infusion System 3.3 Intravascular (Catheter-tip) Transducer Systems
Page 53
53 64
3.4 Blood Pressure Transducer Princ iples 3.4.1 Principles of Operation Operation 3.4.2 Considerations in Evaluation
6 6 66 66 69
3.5 Measurement Errors, Errors, Distortions, and Artifacts 70 3.5.1 End Pressure, Catheter Whip, and Catheter Impact Artifacts ... .70 3.5.2 Respiratory Effects 73 Respiratory Effects 3.5.3 Transducer Zeroing 76
4.0 NONINVASIVE (INDIRECT) MEASUREMENT TECHNIQUES
76
4.1 Auscultatory Measurement 76 4.1.1 Korotkoff Sounds 78 4.1.2 Limitations and Sources of Error. Error. .81 4.2 Automated Noninvasive Measurement Measurement 4.2.1 Auscultatory Measurement 4.2.2 Oscifiometric Measurement Ultrasound und 4.2.3 Doppler Ultraso Measurement 4.2.4 Noninvasive Continuous Finger Blood Pressure Monitoring
86 86 86 87 91
4.3 Correlation Between Direct and a nd Indirec Ind irec t Measurement
91
5.00 REFERENCES 5. ILLUS T RAT ION CREDITS 6.0 ILLUS IBLIOGRAPHY OGRAPHY 7.0 B IBLI 8.0 G L O S S A R Y INDEX
.
.95 96 104 107
SpacelabsMedical: BLOOD PRESS PRESSURE URE
INTRODUCTION This publication presents the principles of hemodynamic This publication hemodynamic pressure measurements of the human cardiovascular system cardiovascular system and discusses the interpretation of the results of current current blo blood od pressu pressure re measurement techniques. The information contained within this monograph provides the technician, clinical engineer and biomedical engineer with a working knowledge of cardiovascular human physiology and the various various technolo technologies gies related to the assessment of human the assessment blood pressure. a quick and The Th e circulatory syste system m pro provid vides es the mechanism for a quick and con of all all the cells which must occur to provide nutrients and tinuous revitalization of remove waste products from the entire entire body. body. The heart, the major power comtwo o pumps connected in series with the ponent of the the circulation, works as tw left ventricle ventricle pushes right ventricle forcing bloo blood d throu through gh the lu lung ngss while the left blood throughout the remainder of the the body. Blood exits the heart’s ventricles into the arteries. Production of art arteri erial al blood pre blood pressu ssure re comprises a complex interaction of many many variables in the the circulatory system. With the heart serving as a pulsatile pump, a given volume of blood blood enters the arteries with each heart beat and produces pressure pulses system. em. These pressure pulses subsequently travel down the in the arterial syst arterial tree in the form of a pressure wave, which changes in configuration as it moves away from the heart. The propagated pressure wave produces arterial pulsations that can be felt a att severa severall locat locations ions throughout the bod body y su such ch as the radial artery in the wrist and the carotidartery in the neck. neck. Arterial Arterial blood pressure is the quantitative measurement of the the observed pulsation. A thorough examination of the quality of the systemic arterial pulsa- the systemic arterial pulsa
any cardiac assessment. Blood pressure measurelions is an integral part of any ments are obtained clinically by both invasive and noninvasive methods. Invasive, or Invasive, or direct, blood pressure monitoring requires gaining access to the requires gaining circulatory system by means of a catheter and recording the pressure of the vessel directly blood within the vessel directly using a pressure transducer. Noninvasive, or indirect, blo blood od pressur pressure e measurement measurement involves the detection of blood pressure without puncturing the skin, usually by employing an occluding occluding cuff. cuff. PhysPhysiological distortion and measurement errors can cause inaccuracy in both the invasive and noninvasive techniques for assessing blood pressure. Such distortions and errors could adversely affect affect the the diagnosis and/or treatment of the varipatient. Therefore, one must become skilled in interpreting the results of variouss blood ou blood pressure pressure measurement measurement techniques.
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Medical: BLOOD PRESSURE Spacelabs Spacelabs Medical:
1.00 ARTERIAL P R E S S U R E P U L S E S 1. 1 . 1 Anatom y and Physiology Physiology of
the Circulatory System
The card cardiova iovascu scular lar system con consists sists of of a se sett of tubes, tubes, known as blood vessels, through w which hich blood flows arid a pump, the heart, that provides the energy necessary to propel the blood. The entire system forms a closed circuit with the blood continuously pumped out of the heart the heart through one set of vessels vessels (arteries) and returned to the heart via a different vessel group (veins). This circulatory system is two distinct circuits: the pulmonary circulation to the composed of two lungs and the the systemic systemic circulation to the rem remain ainder der of the body. Both circuits begin and end at the heart, heart, which which is divided longitudinally into two functional halves. The pulmonary circulation receives deof the oxygenated blood pumped the right side the heart, is oxygenated, is oxygenated, it to to the lungs and returns transports it venous where it from the left side of th the e hea heart. rt. The systemic circulation receives oxygenated blood pumped from the left side of the the heart and delivers delivers it to a all ll the tissues of the the body, including the bronchial circulation, returnir-ing in g th the e deoxygenated blood to the right side of the heart. In both cir vesselss carry carrying ing blood away from the he cuits, the cuits, the vessel hear artt are called arteries veins (Figure 1.1). and tho those se retu returni rning ng blo blood od to the heart are called veins (Figure
off the Heart 1.1.1 Anatomy o The Th e heart is a muscular organ located in th the e chest (thoracic) cavity slightly to the known left le ft of the Itsm. walls of a surfaces sternum. composed special muscle as my myocardiu ocardium. Theare ized muscle ized outer and inner are called are called epicardium and endocardium, respectively A thin layer of cells, cells, the endothelium, lines the heart’s inner surface that comes covered by by a fibrous in contact with the blood. The entire heart is covered sac, the pericardium.
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Spacelabs Med Medicah icah BLOOD PRESSURE
The heart functions as a dual, two-stage pump. Each half of the heart contains tw two o chambers, an atrium and a ventricle, which atrium and are separated ver verticall tically y by an interatriall and interventricular septum, respectively. (Figure 1.2). 1.2). The The atria atria function principally as collecting They also also aid in the final chambers for blood returning to the heart. They ventricles by their weak pumping action. The atrial fifing of the ventricles is small small in the normal unstressed contribution to ventricular filling is forms of heart heart but can be very significant in various forms heart disease. The Th e ventricles supply the e energy nergy necessa necessary ry to propel blood bloodthrou through gh either the pulmonary or the systemic (peripheral) vessel circuits. Between the chambers of the atrium and the ventricle are the atrioventric atrio ventricular ular valves (A-V valves), which are present on both sides of the The e A - V valves (the tricuspid on the right side and the the heart. Th tricuspid on the right mitral on the left side) prevent backflow, or regurgitation, of th the e blo blood od ventricl icles es to the atria during ventr from the ventr ventricu icular lar con contract traction ion (systole)
(Figure 1.3). The aortic and pu the heart pulmo lmonar nary y semilunar valves of the prevent regurgitation from the great vessels, the aorta a and nd the pal(dia-monary artery to the ventricles during ventricular relaxation (dia stole). All these valves close and open passively: that is, they close when a backward (retrograde) pressure gradient develops and open when the forward (antegrade) pressure exceeds the retrograde pressure. The semilunar valves open during ventricular systole and close close during during systole and open during diastole, whereas the A -V valves close during diastole. In a normal resting adult, cardiac output (the rate of blood flow from fro m each ven ventrid tride) e) is approximately five liters/minute. During heavy
work or exercise, cardiac output may increase to as much as 25 liters/minute.
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Spacelabs Medic Medical: al: BLOOD PRESSURE
1.1.2 Arterial System The arterial system transports blood from the ventricles to the capilThe lary networks. In the process of transport, transport, the high-pressure, intermittent blood flow produced by by ventricular ventricular ejection ejection is converted into a relatively constant flow at the level of the the capifiaries. Under resting conditions the blood generally travels from the left ventricle to the peripheral tissues in less than ten seconds. During very heavy two o to three exercise, blood reaches the body’s extremities in as little as tw seconds. Serving as a high pressu pressure re reservoii~ reservoii~the large elastic systemic arteries stretch radially as the stroke volume of blood blood enters the arterial tree from the ventricles. These arteries then decrease in size as blood flows out into the veins between heartbeats. Arterial compliance prevents ance prevents the pre pressu ssure re fm fmm m rising extremelyhigh when th the e blo blood od is pumped into the a arteri rterial al tree by ventricular contraction. This also the heart. the arterreduces the work requirement of the heart. Resifience Resifience of the a high arterial pressure between heartbeats heartbeats so so that blood ies maintains maintains a can continue to flow through the tissues without interruption. leftt sid sidee of th In the systemic circulation, blood leaves the lef the e he hear artt through a single large artery, the aorta. From the aorta, branching These arteries arteries conduct bl bloo ood d to the organs and tissues. These arteries subdivide into progressively smaller branches with the majority branching within the specific organ or tissue. As blood leaves the small arteries, it flows through the arterioles, which are the smallest arterial smallest arterial branches measuring only a few millimeters in length with diameters of act as valves Arterioles control Each which 8 tois 5released 0 microns. through into arteriole blood the capfflary network. branches muscu-many times and supplies ten to to 1 1 0 0 capifiaries. The strong muscu completely obstruct lar wall of the the arteriole can either completely obstruct the vessel or allow it to dilate to several times its its original original diameter, enabling it to greatl gr eatly y alt alter er blood flow to the capillaries. Capillaryflow is also controlled by by changes changes in the precapifiary sphincter, which are small ring ringss of muscular muscular tissue at the junction of the the arterioles and capifiaries (Figure 1.4).
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Spacelabs Medical: BLOOD D PRESSURE Medical: BLOO
Approximately tw two o bfflion capifiaries channel through the peripheral tissues. The total capfflary area produces an effective surface of surface of more more than 500 square meters. Capillaries, which are thin and permeable to small molecular substances, function in the e x — change of fluid, nutrients, fluid, nutrients, electrolytes, waste products products electrolytes, hormones, hormones, and waste (for examp example, le, carbon carbon dioxide [C0 2 ]) betweenthe blood and interstitial spaces. The velocity of blood blood flow is at i its ts minimum at the capfflary level, which maximizes the potential for metabolic exchange. structural turally ly similar similar to the systemic The pulmonary circulation is struc circuit. Blo Blood od lea leaves ves the rig right ht sid side e of the heart throug ugh h the singlelarge the heart thro pulmonary artery~ artery~w which branches into left and right pulmonary arteries. Withi Within n the lungs, the arteries continue to subdivide, forming arterioles and ultimately capifiaries. In these pulmonary capillanes, CO 2 is is exchanged exchanged for oxy oxygen gen,, which bthds to the hemoglobin of the the red blood blood cells.
1.1.3 VenousSystem Blood from the capifiaries enters the venules, which in turn gradu which in ally converge into pro ally progre gressiv ssively ely larger larger veins. veins. In the systemic circulation, veins lation, veins from different organs and tissues unite to form two large veins: the inferior vena cava from the lower portion o of f the body and the superior vena cava from the upper part of the body. The veins primarily provide a conduit for the transportation of blood from the tissues tissues ba back ck to the heart. The venous walls are are both thin arid muscular, which contributes to the veins’ abifity to alter their degree. Increased capacitance by contracting or expanding to a limited degree. Increased capacitance can provide a reservoir for for storage storage of of blood, depending upon the needs of the the body. systemic circulation, blood with low oxygen content In the systemic the heart by way of the the venae cavae. returns to the right atrium of the In the pulmonary circulation, oxygen-rich blood leaves the lungs by way of the the pulmonary veins that empty into the left atrium of the heart.
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Spacelabs Medical: BLOOD PRESSURE Spacelabs Medical:
The pressure in the The the systemic systemic venous venous system is low, maintained by unidirectional valves that allow heart allow blood blood to flow only toward the the heart were re not for these regulatory valves, hydrostatic pres pres-(Figure 1.5). If it we sure (the pressure at any any level level in a fluid at rest due to the weight of
the fluid above it) would produce a venous venous pressure pressure in the feet of a standing adult of about mm m Hg every time the legs about 90 m Hg.. However, However, every move, the muscles contract and compress the veins either in the muscles or in adj adjacen acentt tissu tissues, es, propelling th the e blo blood od forward through the veins. This pumping system, known as the venous pump, acts so efficiently that under ordinary circumstances the veno venous us press pressur ure e in the feet of a walking adult remains below 2 5 mm Hg Hg.. When a person stands perfectly still, perfectly still, the venous pump does not work and the venous pressures in the lower part of the the leg can in incre crease ase to the full hydrostatic full hydrostatic value value of 90 90 mm Hg in about 3 0 seconds. When this occurs, the hydrostatic pressure within the capillaries capillaries also also increases fluid id fro from m the vascular systeminto the tissue spaces. rapidly, forcing flu As a result, the legs may swell and the circulating blood volume may be lost from the vascular vascular system system within the first 1 5 minutes of standing standing circulating blood volume and absolutely stifi. This potential loss of circulating its effects become minimized by numerous compensatory mechanisms found throughout the circulatory system.
Cycle 1.2 1. 2 Cardiac Cycle The period from the end of one heart contraction to the end of the the next is called the cardiac cycle. Each cycle begins with a spontaneous of an electrical ac action tion poten potential tial in the sinoatrial (S-A) node, generation of generation a small mass mass of of specialized myocardial cells embedded in the posterior wall of the right atriu the superior vena vena cava. cava. atrium m near the opening of the S-A -A node serves as the normal pacemaker for the entire heart. The S the normal pacemaker The action potential travels rapidly through both atria to the atrioventricular (A-V) tricular (A-V) node, which lies between the right atrium and the right ventricle, triggering ventricle, triggering atrial atrial contraction contraction a few milliseconds later (Figure 1.6). Th The e action potential is delayed in the the A A -V node for approximately 1 0 0 milliseconds to allow the atria to contract and empty their con into the ve ventri ntricles cles befo before re ventric ventricular ular contraction. Therefore, the tents into tents atria ac actt as primer pumps for the ventricles. The ventricles then pro source of of power the vasvide the major source power for moving blood through through the cular system.
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_ _ _ _ _
Spacelabs Medical: BLOOD PRESSURE
1.2.1 Ventricular Cycle of a period of ventricu The cardiac The cardiac cycle cycle consists consists of ventricular lar relaxation called diastole, followed by an interval of ventricu ventricular lar contraction known as systole. The systole. The systolic systolic phase of the ventricular cyde indudes isovoluniic contraction, rapid ejection, and protodiastole (reduced ejection). Isovolumic contraction, an increase in muscle tension in the absence of fiber fiber shortening, begins with the closure of the atrioventricular valve and ends with the opening of the the semilunar valve. I Imm mmediately after ventricu ventricular lar contractio contraction nbegins, the ventricular pressure rises abruptly as shown shown in Figure 1.7. This pressure increase causes the A - V valves to close, which produces produces the first heart sound (S 1 ). An additional 20 to 30 milliseconds is required for each ventricle to generate a pressure that exceeds the pressure in each great vessel (aorta or pulmonary artery) to open the semilunar valves and iriitiate ventricular ejection’ The Th e ejection period includes the interv interval al fro from m the opening of the semilunar valve to the beginning of protodiastole, protodiastole, when the slow the ventricular pressure pulse gives way to a rapid downslope of the valves are are forced downslope. As shown in Figure L Z the semilunar valves when the open when open the left ventricular pressure increases to slightly above 8 0 mm Hg and the right ventricular pressure rises to to sligh slightly tly abo above ve 8 mm Hg. As the valves open, blood is ejected fr from om th the e ventricles with about 7 0% of the the emptying occurring during the first third of the ejection period (rapid ejection) and the remaining 30% during ejection or protodiastole). Protodiastole ends the next two thirds thirds (slow (slow ejection when the rapidly declining ventricular pressure falls below that of declining ventricular the corresponding great vessel, the aorta or pulmonary artery~arid valvee clo closes, ses, producing the second heart sound (S2 ). the semilunar valv
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The diastolic phase of the ventricular cycle consists of isovolumic The diastolic relaxation, rapid ventricular filling, slow ventricular filling (diastasis), and atrial systole (atrial kick). Ventricular relaxation begins sudden sudden-ly at the end of systole with the closure of the semilunar valve, allowing the pressures to to fall rapidly. rapidly. The ventricular muscle the intraventricular intraventricular pressures continues to relax for another 30 to 6 0 milliseconds although no further change in ventricular volume occurs, giving rise to the period of isovolumic (or isometric) intra isovolumic (or isometric) relaxation. During this time, the intraventricular pressure falls rapidly to a lo low w diastolic value, the A - V valves ventricular filling begins when the atrial open, and a new cycle of ventricular pressure exceeds the ventricular diastolic pressure. The A - V valves open and allow blood to flow rapidly into the indicated ed by the increase in the ventricu ventricles, as indicat ventricular lar volu volume me curve rapid filling lasts for about the first third in Figure 1.7. This period of rapid of diastole diastole and primarily moves blood stored in the atria during vena small amount of tricular systole. Duri During ng th the e next third of diastole, a small blood normally normallyflows flows fiDm the veins, through the atria, and immediately into the ventricles. This middle third of diastole diastole is called diastasis. During the last third of diastole, the atria contract and deliver an additional volume of blood blood into the ventricles, which accounts for approximately for approximately 2 0 to 30 30% % of the filling filling of of the ventricles during each just st cardiac cycle. The volume and pre pressu ssure re of bl bloo ood d in the ventricle ventricle ju as end-diastolic end-diastolic volume and end-diastolic prior to systole are known as pressure, respectively.
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Spacelabs Medical: BLOOD PRESSURE
1.2.2 Atrial Cycle cardiac cycle During Durin g th the e cardiac cycle thr three ee ma majo jorr pre pressu ssure re waves, called a, c, and v, occur in the atria (Figure 1.7). wave ve emanates from the atrial contraction. The right atrial The a wa rises 4 pressure usually usually rises 4 to to 6 mm Hg during during atrial atrial contraction, contraction, whereas whereas 8 mm Hg at this time. the left atrial pressure increases about 7 to to 8 The c wave begins when the ventricles start to contract. It slight backflow results in part from the slight backflow of blood into the atria at the onset of ventricular contraction but is primarily caused by the retrograde bulging of the the A A -V valves toward the atria secondary to incr increas easing ventricular pressure. The v wave wave occurs occurs toward toward the the end of the the ventricular contraction tio n and rises from the slow accumulation of blood in the atria while the A - V valves remain closed during ventricular contraction. When ventricular contraction e end nds, s, the A - V valves open and allow blood ventricles (rapid (rapid inflow phase), which causes to flow rapidly into the ventricles wave to to disappear. the v wave The volume of blood contribu contributed ted to ventricular fifing by atrial varies inversely contraction varies inversely with the duration of the the previous diastole and directly w with ith the vigor of the atrial contraction. Blood normally flows continually from the great veins into the atria. A t slow heart rates, the long diastolic diastolic interval interval permits major ventricular fif ing to take place even before the atria contract. Thus, when diastole conditions), tions), the becomes prolonged (as under resting condi the contribution of atrial contraction may be minor. Th The e heart can continue to operate quite satisfactorily under normal resting conditions even without 30% 0% filling of the ventricles caused by atnial kick. the additional 2 200 to 3 atrial ‘kick’ becomes extremely imporThe volume contribution of atrial tant during rapid heart rates, such as those seen with exercise, and setting of of impaired/reduced myocardial contractility, as in conin the setting gestive heart failure.
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1.3 1. 3 Standard Standard Pressure Pressure Defini De finitions tions Although the term “systolic pressure” technically implies the pressure at any instant during systole, it is conventionally used to denote the peak pressure pressure during a cardiac cycle. Similarly, the term “diastolic to signify signify the minimum pressure during a cardiac pressure” is used to cycle. Pulse pressure is the difference between systolic and diastolic pressure. Mean pressure is the average pressure during a cardiac cycle. It can be derived by integrating the blood pressu pressure re over time, or by use of a low pass filter (coCUtoff ~ 0.05 Hz). if systolic and diastolic pressures are known, known, the mean pre pressu ssure re can be approximated using the following formula (Figure 1.8): Pulse Pressure
Mean Pressure
=
Diastolic Pressure +
3
It should be recognized that the above equation may, at times, be
extremely inaccurate.
2.0 P R E S S U R E TRANSMISSION The blood pressure waveform changes in morphology and ampl ampli the systemic systemic vascular circuit. In the large tude as it proceeds through the systemic arteries, systemic arteries, the peak systolic systolic pressure increases while diastolic and mean pressures remain relatively unchanged in comparison The e pressure begins to drop dramatto aortic pressures pressures (Figure (Figure 2.1). Th
ically in the arterioles and continues to fall in the capifiaries so the mean pressure that began at about 1 0 0 mm Hg in the aorta has decreased to about 1 0 mm Hg at the end of the the capillary network. The pressure continues to decrease to a low of nearly nearly 0 mm Hg in the inferior and sup superior erior vena cava. The pres pressu sure re in the thoracic venae cavae and the right atrium is known as central venous pressure (CVP).
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Spacelabs Medical: BLOOD PRESSURE \_ _ _ _ _ _ _ _ _ _
The pressures in the pu~lmonaryvascular circuit change in a pres-way similar to the systemic pressures with the greatest drop in pres sure occurring in the capillary network. The pressures in the pulmonary circuit, however, are normally much lower than in the systemic circuit, beginning at a mean pulmonary artery pressure of about 1 0 to 1 5 mm Hg and reaching 0 to 5 mm Hg at the left atrium (Figure 2.1).
2.1 Harmonic Harm onic Analysis of Waveforms Blood Pressure Pressure Waveforms In any signal processing application, one should understand the frequency spectrums of the the signal and of the noise. A blood pressure waveform, like any periodic waveform, can be represented by a series, which is a series of weighted shifted sine Fourier series, Fourier weighted and shifted sine waves (Figure 2.2.). The weighting of each each sinusoidal frequency refers to amplitude or modulus. The shif shiftt in time of each frequency the wave’s amplitude component with respect to the other compo components nents repres represents ents the angle. A complete discussion of the Fourier transform wave’s phase angle. is beyond beyond the the scope of this monograph, b bu ut can be found in numer2 ouss texts. ou The components of the human blood pressu waveform are are pressure re waveform expected to to fall fall below 2 0 Hz since a heart rate of 1 2 0 beats per minute (bpm) is well above the normal resting rate and 1 0 times this fundamental frequency is is 2 200 Hz Hz,, a result verified verified by by using Fast Fourier analysis. Figure Figure 2. 2.33 shows the amplitude of the FF Transform (FFT) analysis. FFT T for single for single and multiple beat radial arterial waveforms. In each case, all of the the major frequ frequency ency components are below below th the e 20 Hz limit. FFT T (Figure (Figure 2.3A), 2.3A), 96 % of the For the single beat beat FF the energy i iss less than 93% % of the the energy is 2 0 Hz. For the 5-beat sequence (Figure 2.3B), 93 less than 20 Hz Hz.. Although aortic and pulmonary artery pressures frequency ency comp componen onents, ts, they are also well contain more high frequ represented by components below 20 Hz~
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—
Figure 2.3A Single radial arterial blood pressu Figure 2.3A beat pressure re beat and the magnitude of its Fast Fourier Fast Fourier Transform showthe magnitude ing frequency components below20 Hz (inset shows plot shows plot outto 25 0 Hz, confirming the lack o f high high frequency harmonics).
110100-
0
0.2
0.4
0.8
0.6
Time (seconds)
35.
30-30
25-25
:
C
20
Q) ~
15
L ~ 0
40
80
12 0
I
160
2 00
240
Frequency H, H,))
10-
5.
2
4
6
10 12 Frequency (Hz)
8
14
1 .6
18 18
20
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ulics 2.2 Fundamentals of Hydra ulics aree sim simila ilar. r. The The basic concepts of hydraulics hydraulics and electricity ar hydrauli hydr aulic c analogu analogues es of electrical electrical voltage and current are pressure and flow, respectively. Th The e concepts of resistance and capacitance correspond to each other in both systems. Electrical inductance is analogous to the inertial density density of of the fluid in hydrauli hydraulics. cs. Therefore, Ohm’s Law applies to both systems. Since
~V=IR,
where
A V
I R
—
=
V1
voltage gradient current, and resistance,
=
R
V2
V 1 -V 2 ,
hydraulic analogy requires that the hydraulic analogy AP=QR
where
~ P
Q
R
=
= =
pressure gradient flow, and resistance.
~iQ Q~ =
P2
P 1 -P 2 ,
each case, case, R is actually no In each nott simple resistance but impedance, resistance, capacitan capacitance, ce, and inductance. which is a function of resistance,
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23B B — Series of five radial radial arteri arterial al blood pressure Figure 23 beats and th the e magnitude of its Fast Fourier Transform, showing show ing freq frequency uency components components below 20 Hz (inset shows plot out to 25 0 Hi o f hig high h fr fre e Hi,, confirming th the e lack of quency harmonics). quency harmonics).
x Q)
Time (seconds)
-~ cn
0
Frequency (Hz)
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Spacelabs Medical: BLOOD PRESSURE
2.2.1 Laminar and Turbul Turbulent ent Flow The flow of a fluid through a cylindrical tube can be either laminar ion nor turbulent. Fully developed laminar flow i iss characterized by a io gitudinal. a smooth, wave which front. Thevelocity fluid in profile the center center of the with parabolic the highest ye exhibits the tube flows locity and the fluid at the vessel walls actually does not flow at all (Figure 2.4). Turbulent flow i iss characterized by disorganized flow in many directions, with many eddies (Figure 2.4). The dimensionless parameter known as Reynolds’ Number (Re) predicts whether flow wifi be laminar or turbulent through a cylindrical tube. Re—
VdQ
fluid (cm/second) where ~ = mean velocity of fluid d = diameter of tube (cm) = density of fluid fluid (gm/cm 3 ) r j = viscosity of fluid (Poise). fluid (Poise). If Re exceeds 200, turbulent flow begins at the points points where fri i tubes. If R e exceeds 2000, flow will be turbulent branches occur fr even in smooth, straight tubes. The viscosity o blood is generally of f blood about 0.03 Poise and the density of of blood, blood, about 1.05 (since it is mostly water) In the the normal human circulatory system the primary sites for turbu’ent flow are the aortic arch and the pulmonary artery Dur ejection of blood from the ventricles, the high velocity velocity of of ing rapid ejection blood and the transient increase in diameter of these vessels contribute ut e to raising R e to several thousand units, causing turbulent flow. In the large arteries, R e normally reaches several hundred units at major branches, leading to some turbulence at these sites also. Certain cardiovascular cardiovascular conditio conditions ns may produce turbulent blood flow which, in turn, increases the workrequ requirement irement and energy expendthe work the heart. iture of the .~
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SpacelabsMedical: BLOOD PRESSURE
Viscosity represents represents the resistance to flow due to the internal the internal of the fluid. Newtonian fluids are those whose viscosity refriction of friction mains unaffected by flow rate while nonNewtonian fluids exhibit a viscosity which is a function of flow conditions. Since blood is essentially a essentially a suspension of particles particles (blood cells) in a watery liquid (plasma), the viscosity of blood depends on flow ow on several several factors: 1 ) as fl viscosity increases decreases, viscosity increases (that i is, s, blood is a nonNewtonian fluid); hematocrit (percent of blood volume composed of red blood 2) as the hematocrit (percent of cells) increases, visco viscosity sity incr increases; eases; 3 3)) when the blood blood reach reaches es arterioles of about about 1 mm in diameter, the blood cells, which are saucer shaped, seem to align along the direction of laminar laminar flow, thereby reducing viscosity; and 4 4)) in the capillaries, the blood cells squeeze single file file order, increasing the apparent viscosity. through in single
2.2.2 Poiseuille’s Law An expansion of the the hydraulic analog of Ohm’s Law is Poiseuille’s Law for steady laminar flow of a Newtonian fluid through cylindricall tubes. ca Law (hydraulic analogy): (hydraulic analogy): Ohm’s Law
where
Q
Q
=
A~P
flow, A P = pressure gradient, P 1 P 2 , R = resistance. =
-
Poiseuille s Law:
Q ..
where
Q
=
APrrr4 8 ~ L
R = resistance = 8riL
flow, A P = pressure gradient, P 1 r = radius of tube tube (cm), = viscosity of fluid fluid (Poise) (Poise) L = length of tube tube (cm). =
-
27
Figure 2.5A
— Determination of vascular impedance. Pressure and flow pulses have been resolved into mean Pressure values and a series of harmonic harmonic sine waves.
Pressure Pre ssure pulse
Flow pulse
MEAN PRESSURE
MEAN FLOW
+ Harmonic
/ / / / / / / ‘
~ ‘
~
2
I ‘I
I’ S ~
/
3
I ~
~I
‘
I
/ ‘ I ~
‘
,
/
/ ‘ /
“I
/
~I
-,
-
,‘
‘s_I
\
-‘
,‘ /
~
,‘
‘ F ~_
.%
% I% ~
F % l~ I
VV\JVV
28
Spacelabs Medical: BLOOD PRESSURE
Poiseuffle’s law is based upon three ass assumptio umptions ns that do not strictly apply to bl bloo ood d flow: flow is not entirely laminar in a all ll parts of the the circulation (See circulation (See Section 2.2.1); blood is not a Newtonian fluid, since Section 2.2.1); viscosity sity chan changes ges with flo flow w rat rate; e; and blood flow is not steady, bu its visco butt How wever, the relationship pulsatile, in most of the arterial tree. Ho described does does apply apply in a qualitative manner and i iss projected to be very accurate in the small arterioles and capillaries.
2.3 2. 3 Vascular Impedance I mpedance Concepts Concepts Blood pressure, flow, and vascular impedance are closely related. Given any tw two o of these these three measurements, the third can be calculated.
2.3.1 Measurement (Calculation) Calculation of vascular of vascular a complex acquisition task for tw two o of reasons, reaso ns, impedance i iss Clinically, one clinical and acquisition one mathematical. simul taneous pressure and flow measurements at the same anatomic site is not a simple task. Mathematically, the pulsatile nature of hemodynamics produces an produces an impedance that i iss not a single value but a frequency dependent spectrum of amplitudes amplitudes (moduli) arid phase angles. T o calculate im imped pedance ance,, the measured pressu pressure re and flow waves must be sorted into their frequency components by by Fourier Fourier analysis (Figure analysis (Figure 2.5A). Then impedance is determined for each corOhm’s Law. The impedance amplitude at responding frequency by Ohm’s Law. each frequency frequency represents the relationship between the magnitude of at that angle at angle at wave Th The e phase each and pressure pressure and and flow that frequency frequency time frequency delay between represents the the pressure the flow wave. Mean vascu vascular lar resistance is the most frequently used mean n fl flow ow are most easily parameter because mean pressure and mea measured. The mean resistance (terminal impedance) value has an amplitude, but no phase angle angle since since mean pressure and flow are DC values.
29
Figure 2.5B — Vascular impedance in th the e femoràl artery of the of thedog dog under control conditions (left); during vasodi-
lation (middle); and durin during g vasoconstriction (right) Closed circles representdata obtained from Fourier analysis of one one pair of pressure and flow waves.
VASCULAR IMPEDANCE
60
Control
Vasoconstriction
Vasoclilation
~I) > ~
40
x
20
4
Hz
-0.5 -1.0
8
Hz
112
16
I
4
I
8
I
12
16
30
SpacelabsMedical: BLOOD PRESSURE
Measurement of of vascular vascular impedance is further complicated by vasoconstrictive state state of the the fact that it constantly changes as the vasoconstrictive vessels changes. blood vessels changes. Figure 2.5B shows an impedance spectrum for the same animal in nor (low resistance), and normal, mal, vaso vasodila dilated ted (low vasoconstr vasoc onstricted icted (high resistance) states. resistance) states.
2.3.2 Physiological Importance The impe The impedanc dance e spectrum contains much irifomrntion abo abou ut th the e physical state of the vascular system. First, First, an increase in the characteristic impedance average of moduli moduli >2 Hz represents represents a a sign sign of reduced reduced larger arteries. A shift in the frequency at which compliance of the the larger arteries. A hi i either minima and maxima appear signals a change h either wave veloci sites. An impedance spectrum can ty or in the dominant reflection reflection sites. or in demonstrate circulatory abnormalities such as those fou found nd in patients systemic vascular vascu larons disease. with hypertension due to osci size of the oscillati llations of imAn increase in or thepulmonary the frequency-dependent pedance suggests increased reflection originating in the distal part of the arterial tree or in the microcirculation. Additional findings would inc inclu lude de an increased terminal and perhaps characteristic imdue e to increased mean vascular resistance and reduced pedance value du compliance, respectively.
2.44 Mean Blood 2. Blood Pressure Transmission: DC D C Analogy Analogy This section presents how the the direct direct current current (DC) (DC) component of blood
pressure generated in the left ventricle changes as it travels through the hydraulic circuit of the systemic circulation. Pulmonary mean discussed briefly. pressure wifi also be discussed briefly. Mean arterial pressure i iss chiefly maintained by the capacitive effect of the aorta. If the the systemic vasculature were noncompliant, leftt ventr ventricle icle would the very high pulsatile pressure generated by the lef be tran transmi smitted tted directly to the the capifiary capifiary beds and pressu pressure re in the aorta would drop to near zero between contractions of th the e hea heart. rt. However, since the aorta can stretch, it it stores stores some of pressure the initial pressure of the pulse, which is released after the aortic aortic valve valve closes. The release of occur urss as blood flows out through through the pressure occ the periphery during yentricular diastole. tricular diastole. This effect is very similar to that of a capacitor in a half wave wave rectifier circuit (Figure 2.6).
31
Figure 2.6 — Comparison of left ventricular function and its electricalanalog, its electricalanalog, the capacitor~coupledhalf-wave rectifier. N mimics cs ventric ventricular ular pressure Note ote that th the e voltage V mimi 1 and V mimics aortic pressure. The diode D in th recti- the e recti 0 fier circuit represents the aortic valve an and d th the e RC load circulation. the th e represents peripheral
+t
D P1
Capacitor-coupled half-w half-wave ave rectifier
Aortic valve closes (incisura)
E Aortic pressure
E
C-,
Left ventricular pressure
32
Spacelabs Medical: BLOOD PRESSURE
Transmission of mean pressure depends primarily on the Figure re 2.7 2.7 resistance of the vascular bed and not on compliance. Figu shows the progressive decline of mean mean pressure from the the aorta to vena cava. The major pressure drop occurs in the arterioles arterioles since the vena the pressure drop than other the system. they have higher resistance than other components of the drop minimizes the pressure at the capillary level and This pressure pressure drop thus promotes a minimum flow velocity for optimum exchange of oxygen, nutrients, arterioles les also have nutrients, and waste products. The arterio “precapifiary sphincters” that can contract or relax and selectively to various change the amount of blood flowing to various parts of th the e bo body dy (See Figure 1.4). For example, follow following ing a meal, the sphincters to the capillary beds of the the stomach and intestines relax, which increases blood flow and aids digestion. Several factors contribute greatly to the resistance properties of the the vascular system. First, as arteries branch and become more narrow.. Since resistance varies numerous, they also become more narrow inversely with the fou fourth rth pow power er of the vessel radius (See Poiseuille’s greatly ly incr increase ease vascuLaw, Section 2.2.2), this narrowing tends to great lar resistance. However, the arteries also imdergo extensive branching as they However, narrow, thereby increasing the total cross-sectional area in relation to the preceding vessels. The area inaeases at a rel relati ativel vely y steady rate through the aorta, large arteries, and arterioles, but increases more rapidly in the capifiary beds (Figure 2.7). Blood flow is significantly capfflar fflary y level since since velocity velocity i iss inversely proportional reduced at the cap to the cross-sectional area. The same same effect effect occurs when a rapidly flowing stream encounters a sudden widening and/or deepening, slowhig the flow of water water dramatically.
33
presentation of changes changes in th the e Figure 2.7 — A graphic presentation cross-sectional area of th the e vascularbed, th the e average flow velocity, and th the e meanpressure in various segments of the circulation.
Ct~
C-
CO
-~
.2
5-
5-
cC
a)
Ct CO
5-
0
CO
= •6~ ft
U
ft
a)
C -) CCC
0 a)
>
C a)
>
ft
C a)
>
.40
600
500 50 0
•30
Ct
a) 5-
C~ ) C )) CO
400
E
E
C)
ft
a)
0 C)
300
U
20
Ct
U 200
10 100
0
a) >
34
~~Spacelabs Medical: Medical: BLOO BLOOD D PRESSURE
vascular ar resist resistance ance and mean pres The thi The third rd factor operating in vascul pres-sure transmission is the law for total resistance of parallel resistors. Parallel hyd hydrauli raulic c resistance is calculated in the same w way ay as parallel electrical resistance:
_ _
1 D
“total
where
R
=
=
1)
1
1
1
+ fl + T) +
1\3
T)
JX
+
4
resistance.
Since capifiaries exist in parallel, these these vessels’ vessels’ very high indiare essentially essentially negated and the total resistance of vidual vidu al resistances are the capillary beds remains very low, which accounts for the very small mean pressure drop across them.
the venous venous system drops very gradually to Mean pressure in the nearly zero in the right atrium. The res resist istanc ancee of the venules and veins must mu st ther therefo efore re be very low to allow blood flow propelled by the 1 0 mm Hg pressure gradient between the end of the the capillaries and of about about 9 0 mm Hg. the right atrium compared to the arterial gradient of Mean pressure in the pulmonary circulation undergoes analogous changes b bu ut of a lower magnitude because the pressure in the pulmonary circulation is much lower than in the systemic circulation. Since blood flow through the aortic and pu]rnonary valves is identical, resistance must be much lower in the pulmonary circuit with Ohm’s Law applying in this case also. Resistance through the blood vessels is controlled primarily by constriction and dilation of the the vessels at the sites of resistance resistance leading to the capifiary networks. Since it cannot be directly measured, resistance is calculated from measurements of blood flow and example, if if the pressure differpressure difference in the vessel. Fo Forr example, ence between tw two o points in a blood vessel i iss 1 mm Hg and the flow rate is 1 milliliter/second, the resistance equals one ( 1 ) peripheral resistance unit (PRU) in mm Hg/milliliters/second. Other measures of vascular vascular resistance that are sometimes used include the “Wood unit” (mm Hg/liter/minute) and the vascular resistance unit (VRU) (dynes x second/cm5 ) (See (See Table Table 2.1). The VRU is the measurement of vascular resistance vascular resistance most commonly used in the the clinical setting.
35
At rest, the rate of blood flow through the circulatory system measures nearly 1 1 0 0 milliiterslsecond. The pressure difference from the systemic systemic arteries Hg.. arteries to the systemic veins equals about 1 0 0 mm Hg resistance (systemic vascular resistance) peripheral Therefore, the 1 total approximates some physiologic physiologic conditions conditions PRU. in which a ll the In some body become very constricted constricted (for (for exblood vessels throughout the the body ample, shock), the total peripheral resistance increases to as high as 4 PRU. When the vessels become greatly dilated, total peripheral resistance can fall to a low of 0.2 0. 2 PRU. Systemic vascular resistance calculated as follows: (SVR) is calculated as SVR SV R (dynes sec/cm5 )
where MAP CVP
Co 79.92
= =
= =
=
MAP-CVP Co
x 79.92
mean arterial pressure central venous pressure (mean right atrial pressure) cardiac output (liters/minute) conversion factor conversion factor (Wood Units (Wood Units to to VRU).
In the pulmonary system, the mean arterial pressure averages 1 6 mm Hg and the mean left atrial pressure averages 2 mm Hg for a net pressure difference of of 11 4 mm Hg. The total puJmonary resistance at rest approximates 0.14 PRU. This can increase under certain disease conditions to as hi phys-high as 1 PRU and can fall during some phys iologic states, such as exercise, to as low as 0.04 PRU. Pulmonary vascular resistance (PVR) can be calculated as follows:
P V R (dynes sec/cm5 )
where M P A PCWP
Co 79.92
=
=
=
=
=
M P A - PCWP co
x 79.92
mean pulmonary artery pressure pulmonary capillary wedge pressure (mean left atrial pressure) cardiac output (liters/minute) conversion factor conversion factor (Wood Units (Wood Units to VRU).
36
Spacelabs Medical: BLOOD PRESSURE
TABLE 2 .1 Correlation of measures measures of vascular resistance.
Unit 1VRU (dyne sec/cm5 ) 1 Wood Unit
VRU
1
0.0125
Wood Unit
80
1
PRU 1333.33
16.67
(mm (m m Hg/i/mm)
1 PRU (mm Hg/ml/sec)
7.5 x 10~
0.06
1
Diastoli Pressure a n d Diastolic 2.55 Systolic 2. Transmission: A C Anal AC Ancalogy ogy When the blood pressure wave reaches the capillary level, it has essentially lost essentially lost its alternating current (AC) components and only a alternating current mean pre pressu ssure re remains. The transformation from the large A AC C pressure component with a DC offset in the aorta to DC on only ly in the capillanes is not a simple attenuation (Figure 2.1). Systolic pressure ris e s as the pressure wave moves tow toward ard the periphery then it falls along with mean and diastolic pressures. T This his increase in systolic pressure appears as the most visible result of a large number of changes changes in pressure waveform morphology as it traverses the arterial tree. Arteriosclerosis, which commonly occurs in older people, the arteries and thereby greatly reduces reduces the compliance of the their ability to store pressure. This This resu results lts in more direct transmission of the high pressu pressure re of ventricular ejection to the periphery and consequently higher pulse pressure than is normal. The distinction between pressure and flow and the propagation of each each is important in the transmission of the A C portion of wave travels travels down the arterial tree the blood pressure. The pressure wave much more quickly than the flow wave. This occurs in fluid dynamics in general. The visible part of a wave in a lake or ocean is actually wave travels travels much more the pressure wave, while the water in the wave slowly An object floating in the water moves with the water. As waves pass underneath the object, it appears almost stationary.
37
2.5.1 Damping o f High Frequencies aortic valve valve closure closure is p The incisura caused by aortic pres resent ent only only in blo blood od pressure waveforms measured in the upper aorta. This occurs because the capacitive nature of the the arteries and the inertia of blood blood tend to dampen the high frequency components of blood pressure. Since the incisura is composed of high high frequency harmonics c co ompared to the rest of the the waveform, it disappears alter a rather short journey jou rney down the arterial arterial tree. tree. This damping also also slightly slightly reduces systolic pressure because the very steep slope dur during ing rapi rapid d ejection consists of high freq frequency uency harmo harmonics. nics. The filtering effect is of minimal factors rs affec affectt systolic pressure importance, however, because other facto to a much greater extent.
Tapered Tube Effect
2.5.2
wave travels travels down a progressively narrowing tube, it becomes As a wave amplified du due e to the concentration of its its energy into a smaller area. effect occurs occurs when an ocean wave travels into an inlet or when This effect sound passes through an old style earhorn. In the circulatory system, the tapered effect of smaller smaller blood vessels would seem to explain the systolic pressure amplification in the periphery, but its contribution is thought to be minimal due to the extensive branching of blood blood vessels.
2.5.3 Frequency Dispersion is that well-known occurring Another phenomenon in the circuhtion wave velocity is directly to frequency. the pressure proportional waves trav travel el fast faster er than lower freHigher frequency components of waves quency components. For example, example, if a stone is dropped into a stifi ripples will will disperse as they move away from the pond, the resulting ripples splash site into faster moving high frequency ripples and slower moving low frequency ripples. Similarly, the high high freq frequenc uency y harmonics of a blood pressure waveform wifi propagate somewhat more quickly thar~ quickly thar~ the low frequ frequency ency harmoni harmonics, cs, resulting in distortion of the waveform as it travels away from the heart.
38
Spacelabs Medic Medical: al: BLOODPRESSURE BLOOD PRESSURE
2.5.4 Pressure W av avee R efl eflecti ection on An impedance mismatch, such as that seen at the junction of the the arteries and smaller arterioles, results in the retrograde reflection of a portion of the antegrade pressure wave. When the blood pressure the antegrade waveform is measured upstream from a a reflection reflection site, site, a hump appears, superimposed on the original transmitted pulse wave. This reflection is the pri primar mary y mech mechanism anism for amplification of the peripheral systolic pressure. Figure Figure 2. 2.88 shows a series of series of pressure tracings as recorded from a dog’s aortic valve to the femoral artery using a high fidelity fid elity cathete catheter-tip r-tip measurement system. Note the early disappearance of the appearance of two two refl reflected ected waves, one the incisura and the the appearance early and one relatively late. late. Three Three or more reflectance waves are not uncommon, depending upon the measurement site and the condition of the the subject’s vascular bed. A large reflectance hump is frequently misidentified as the incisura, even though the mechanisms of their production are are completely completely different. The fo foot ot of a ref reflec lectan tance ce hump (dicrotic oscifiation) should be referred to as a dicrotic notch semilu ilunar nar valve dosure. Early researchwhereas the incisura denotes sem valve dosure. ers believed that the major reflection occurred at the bifurcations or branches of the arteries, but more recent studies have supported the hypothesis that the majority of the reflection is du due e to vas vasoco oconst nstri ric c small arter arteries, ies, arter arteriole ioles, s, and precapfflary sphincters and the tion of small resulting impedance mismatches~
39
Spacelabs Medical: BLOOD PRESSURE
3 . 0 I NVA SIVE ( DIRE CT) M E A S U R E M E N T TECHNI TECHNIQU QU ES As the name implies, implies, invasive invasive measurement of blood pressure blood pressure involves gaining access to the vascular system by inserting a catheter into an artery or vein. The catheter is usually coupled via a fluid-filled tube tu be to a pressure transducer outside the body. The fluid-filled catheter-tubing-transducer system possesses unique characteristics that mu must be considered when int interpre erpreting ting the pressure waveforms. Catheter-tip transducers that are introduced directly into the circulatory system are also available. However, because o of f their their fragility fragility and expense they are generally used only in research. only in
3 . 1 Pressure Measurement Sites Measurement Sites of Clinical Interest Interest
There a are re two two basic basic methods for inserting a catheter into a blood vesThree variations sel: percutaneous and surgical cutdown. Three sel: variations on th the e percutaneous technique are ifiustrated in Figure 3.1. Vessel cutdown is a su~ica1technique used to insert a catheter into a blood vessel in cases in which percutaneous insertion is not practical. A practical. A small incision is made in the skin, exposing the underlying vessel. The catheter i iss then introduced through another small introduced through incision in the vessel. Catheters used for direct blood pressure monitoring fall into central two general peripher perip heral al or Catheters on forwhether arterial pressure is categories monitored. depending peripheral pressure of teflo teflon-coate n-coated d plastic and monitoring are constructed of and measure measure 3 to 1 3 cm in length. length. These These catheters have an end hole and a single l u — men for measuring pressure and for withdrawing blood samples. for central central pressure monitoring are used to measure presCatheters for sures on on the right side or on on the left side of the the heart. Pulmonary catheters, also also known as as Swan Swan G an z T M or right heart catheters, artery catheters, are multi-lu multi-lumen men mod models els that have an end hole, multiple side ports, an inflatable balloon on th the e tip tip to aid in positioning, a thermistor for measuring blood temperature at the tip, and, sometimes, optical fibers for of for pacblood ing measurement the heart. are electrodes used to measure heart. Pu Pulmo lmonary naryoxygen artery arter y saturation catheter cath eterss and
41
Spacelabs Medic Medical: al: BLOOD PRESSURE
central venous, puilmonary artery and pulmonary capfflary wedge pressures an calculate cardiac cardiac output by measuring temperature and d to calculate changes of flowing flowing blood (thermodilution principle). Left heart a single lumen cath catheters eters to general gen erally ly have multiple side ports C with and are used to measure pressures in the left ventricle and aorta. en measure tral pressure catheters range from 3 0 to 1 0 0 cm in length. Catheter diameters are designated by one of tw two o scales, the Stubbs gauge sca].e or the French ( F ) scale (Table 3.1). Adults usually require a 4F to 5F catheter for peripheral blood pressure monitoring 5F F to 8F catheter for central pressure monitoring and cardiac and a 5 catheterization.
3.1.1 Peripheral A rterial erial P ressur Peripheral A rt ressuree Peripheral (systemic) arterial blood pressure is the standard meas of hemodynamic status used in intensive care care units units and dururement of ing surgery Th The e most com common mon site for continuous measurement arterial pressure in adults is the radial artery located in the wrist. This site is the first choice because of its easy access both for catheter placement and for subsequent catheter manipulations. In addition, the radial artery parallels the ulnar artery on the other side of the the wrist, which continues to supply blood to the hand if the radial artery as a result result of of the should become temporarily or permanently blocked blocked as catheter cathe ter placemen placementt (Figure 3.2). Other sit sites es for placement of peripheral arterial catheters include the brachial, axillary, femoral, and and dor (Figures 3.3A 3.3A and 3.3B, respectively). salis pedis arteries (Figures Arterial pressare monitoring in children is done at the same sites as in adults. In newborn infants, the umbilical artery is used In newborn for pressure monitoring and blood sampling.
43
3.11 Common Hypodermic Needle Sizes and TABLE 3. Intravascular Catheter Dimensions
Catheter Sizes French Outside Scale Diameter (mm)
Needle Sizes Stubbs Outside Gauge Diameter (mm)
3F
1.00
20 Ga
0.9
4F
1.33
1 8 Ga
1.25
1.67
1 6 Ga
1.65
5F 6F
2.00
1 4 Ga
2.1
7F
2.33
1 3 Ga
2.4
8F
2.67
1 2 Ga
2.75
Adapted from Geddes L A : Cardiovascular Devices and Their Applications. New York: John Wiley and Sons, 1984, p. 43.
44
3.1.2 Central Venous and Pulmonary Artery Artery P P ressur ressures es In pediatric and adult intensive care units, it sometimes becomes more com complet plete e picture of the patient’s necessary to have a more hemodynamic status than is provided by the peripheral arterial pressure alone. In such cases, cases, the pressures in the right atrium, right ventricle, and pulmonary artery must be measured directly. These pulmo-pressures are continuously monitored monitored usin using g a multi-lumen, pulmo nary artery (P A ) catheter (Figure 3.4) inserted into a lar large ge vei vein n such subclavian vein in the shoulder or the internal jugular vein as the subclavian vein in the neck. The catheter has a balloon on i its ts tip that can be inflated to act as a “sail” to allow the flow of blood to direct the catheter through the right atrium and ri righ gh t ventricle and into the pulmonary artery. T he catheter is positioned so that, when the balloon i iss intermittently inflated, the catheter t tip the small ip will “wedge” in one of the pulmonary arteries to to measure measure the pulmonary capifiary pressure (Figure 3.5). The The ballo balloon on is then deflated and the pulmonary artery pressure i iss monitored continuously through the same lumen at the tip of the pressures obtained through the pulmonary the catheter. The pressures artery catheter include the following: Venous us Pressure 1) Central Veno Pressure (CVP) (CVP)
Also referred to as right atrial pressure (RAP), the CV P is monitored through a side hole that lies in the right atrium or pulmo-superior vena cava, about 3 0 cm from the the tip of the the pulmo nary artery (PA) catheter. The The CV CVP P can also be measured a single single lumen through a lumen end hole catheter inserted specifical measurement serves ly for that purpose. This blood pressure measurement serves as an indicator of the efficiency of the the right ventricle’s ventricle’s pump pumpCVP P is usually elevated in coning action. Fo Forr example, the CV ventricle icle is unable to pump gestive heart gestive heart failure when the right ventr out of the the heart the total amount of blood returning through The C CV V P does not normally exhibit exhibit a a large pulsa pulsa-the veins. The tile variation and is usually reported as a mean value. Normal 0-88 mm Hg. mean C\TP is approximately 0-
48
Spacelabs Medical: BLOOD PRESSURE
TABLE 3. 3.22 Adult Cardiovascular Pressures Normal Values
Pressure Systemic Arterial Systolic Diastolic Mean
Pulmonary Artery Systolic Diastolic Mean
Pulmonary Capifiary Wedge Pressure* Wedge Pressure*
Right Atrial* Central Venous*
Right Ventricle Systolic End Diastolic
Left Ventricle Systolic End Diastolic
Abbreviation .
SP DP MAP
PA S PA D M PA
Normal Value (mm Hg Hg) )
9 0 140 60 90 7 0 105
1 5 30 4 - 1 .2 9- 1 6
-
-
-
-
PCWP
RAP, CVP*~ RVSP RVEDP
LVSP
LVEDP
1
-
10
0- 8
1 5 - 30 0 8
90 1 4 0 5 12
-
-
their mean *pQi\TJ) RAP, and CVP are listed as their mean values. ~RAP and CVP refer to to the the same measurement and are used interchangeably.
-
51
Right Ventricular Pressure (RVP) 2) Right Ventricular Right ventricular pressure is measured via the distal end hole while the pulmonary artery catheter is being advanced through the ventricle and i iss usually not monitored continuously. Normal right ventricular pressures a are re listed in Table 3.2. 3) Pulmonary Artery Pressure (PAP)
Pulmonary artery pressure is measu measured red throu through gh the end hole of the the PA catheter. Systolic, diastolic, and mean P A P aid the clinician in developing a total hemodynamic profi profile le of the patient (See Table 3.2). 4) Pulmonary Capifiary Wedge Pressure (PCWP)
pulmo-positioned ned pulmo When the balloon on the ti tipp of a properly positio nary artery catheter is inflated, the blood flow pushes the balloon into a “wedged” position in one of the the pulmonary artery branches. The balloon stops al stops alll blood flow in the artery branches. The arteriole and capifiaries, therefore no pressure gradient exists between betw een the catheter tip and the distal distal pulmonary pulmonary veins. Since left atrial atrial pressure i iss ne the difference between PCWP and left neg gligible, the PCWP serves as the clinical equivalent equivalent of of lef leftt atrial atrial pressure. The PCWF~like the CVP, is usually reported as a ranging ing fro from m 1 to to 1 1 0 mm Hg Hg.. mean value with normal PCWP rang
tricular cular a ressures es 3.1.3 Left Ven tri ann d Aortic P ressur The left ventricular and aortic pressures are measured during a left heart catheterization. A single-lumen catheter i iss advanced with the aid of of fluoroscopy fluoroscopy against th or femoral the e blo blood od flow from the brachial or femoral artery into the aorta and through the aortic valve into the left ventricle. The measured pressures provide information about the pumpcle. ing ability of the left ventricle and the functioning of the aortic valve. than This is a brief, diagnostic procedure that carries a higher risk than either peripheral arterial or central venous pressure monitoring and is only performed by a specially trained cardiologist.
52
Spacelabs Medical: BLOOD BLOOD PRESSURE PRESSURE
3.2 3. 2 Fluid-filled Systems Systems 3.2.1 Determination a n d Optimization o f esponse esp onse Frequency Rdynamic Knowledge of the dynam ic response of a direct measurement system ensures accurate accurate interpretation interpretation of the the obtained readings. The frequency response of a measurement systemcan generally be defined by the determination of two two parameters, the damping ratio (j3) and the determination value of of either the natural frequency (c o 0 ).). If the the value either of these these parameters falls outside of acceptable ranges, distortion of the measurement may result. The freq frequency uency response of a system can be mea measu sured red by forced oscifiation or free oscillation P Forced oscifiation involves using a waveforms of known sinusoidal pressure wave generator to input waveforms known frequency and amplitude into the measurement system of interest interest and assessing the ratio of output output amplitude to input amplitude. B y varying the input frequency over the range of inter interest est (tha (thatt is, 0 to 1 0 0 Hz), the complete frequency response profile can be determined. This method provides a more accurate and complete assessment of the frequency characteristics of the the system than the free oscillation technique, b bu ut it is only applicable in the laboratory setting. The free oscifiation method consists of using the time domain response of a system to a step input to determine the natural frequency and and damping damping ratio. This method is more practical for measuring the frequency response than the forced oscifiation approach for severit works works in eit setting, it does al reasons: it either herthe the laboratory or clinical setting, not require a sinusoidal pressure generator or a reference transducer, available materials. and it can be performed using readily available materials.
53
~SpaceLabs Medical: BLOOD PRESSURE
Figure 3.7 T he transient oscillatory response of a application of a a pressure catheter transducer system on application square wave. —
x2 x4
~
To determ determine ine the ratio of x~ 1x , use an 1 1 ratios s average of the ratio for th the e first several peaks.
=
/
2 in (x~ + Ix~) 2 1 + in (x~ + Ix~) 1
=
1
T ~ i~ 1 3 2
—
-
55
Figure Figure 3.8 — Frequency response curves of a pressure measurement system, illustrating the importance of optiinal damping.
0 0 (t
a)
-u
0
0-
E
.cC .c C
0
20
40
60
80
100
120
140
Input frequency as percent of natural frequenc frequency y
160
180
200
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Spacelabs Medic Medical: al: BLOODPRESSURE BLOOD PRESSURE
requires a a simple In the laboratory the free oscillation method requires arrangement of the type shown in Figure 3.6. The end of a large syringe is cut o off ff and the tip of the catheter i iss inserted into the syringe barrel through a rubber stopper. A balloon i iss sealed around the the open open end of the syringe with an 0 ring or or ru rubber bber band and inflated using a sphygmomanometer bulb. When the balloon is ruptured ruptured (prefer (preferably using a flame to avoid the transient transient pressu pressure re increase associated with needle puncture), a step decrease in pre pressu ssure re is applied to (ass the measurement system. Assuming the system is underdamped (a are most catheter-transducer systems), the response resembles that The e damping ratio and natural frequency are shown in Figure 3.7. Th determined as shown in this same same Figure. Figure. When applying this technique, however, one should remember that these calculations are based on th the e assu assumpti mption on that the dynamic behavior of the catheter-manometer system is characterized by a second order differential equation. While this approximation this approximation has been shown to be adequate for most catheter-manometer systems, one mu must st be alert for possible deviations fr from om secon second d order behavior. Ideally, co~sh should ould be above 2 0 Hz and / /33 near 0.7. These values ensu ens ure tha thatt the ratio of output to input (amplitude ratio) remains near 1 (± 5 %) %) fr from om DC to to 2 200 Hz Hz.. A decrease in / 3 (underdamping) results in amplification of the components of the the input signal near the natural natur-frequency and attenuation of frequ frequency ency components above the natur cause a a false increase in the al frequency (Figure 3.8). Th This is ma may y cause the systolic blood pressure reading because the high frequency portions of pressure reading
the blood pre pressu ssure re waveform contribute primarily to systolic pressure and the low frequency com compon ponent entss to diastolic pressure. Since signal, it it is unmean pressure represents the DC component of the signal, affected by changes in damping. An increase in / 3 (overdamping) causes attenuation of the signal components beginning below the natural frequency, leading leading t too underestimation of systolic systolic blood pres overestimation of of diastolic blood pressure. sure and, insevere cases, overestimation Figure 3.9 shows the frequency response, step response, and waveforms for for ideally damped, underdamped, and representative waveforms overdamped systems.
57
Figure 3.9 — The representation of the frequency response, step response, and representative waveforms for ideally damped, under underdam damped, ped, and overdamped blood pressure measurement systems.
Ideally Damped
Unde nderdamped rdamped
Frequency response
Step response
~
Representative waveform
Overda mp e d
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Spacelabs Medical: BLOOD PRESSURE
The frequency response of a catheter-transducer system can be optimized in the the clinical settin setting. g. The approximat approximate e equivalent circuit for a catheter-transducer pressure pressure measurement system is shown
in Figure 3.10? It can be found from this circuit that: from this
1
VLCc
and
T o a large extent large extent the physical of with the system characteristics A transducer a stiff itself determine the frequency response. diacapacitance nce,, meaning that registration registration of of a change phragm has a low capacita the diaphragm in pressure requires only minimal displacement of the movement of the and therefore only minimal minimal movement the fluid through the high resistance catheter. Th The e use of a large diameter, short, stiff catheter catheter with as little tubing and as few stopcocks as possible between catheter will optimize by decreasing decreasing L L 0 and R~. and transducer will optimize both / 3 and co~by these factors are usually predetermined by pracAlthough some of these of patient care care (for tical constraints of patient (for ~amp1e, stopcocks for blood drawing), some can be controlled. For example, several commercially a var variab resistance that to produced insert damping between the catheter and the devices increase iable thele resistance coefficient transducer to transducer damping simple screw screw without lowering the natural frequency are available. A simple clamp that partially crimps the tubing can also be used for this purpose.
59
Figure 3.10
The representation of the approximate The circuit for for the optimization of a catheterequivalent circuit —
transducer system.
Vi’
V~ = blood pressure waveform = inertance of catheter and tubing = resist resistance ance of catheter an and d tubing = capacitance of transducer V = output waveform 0
illustration of Figure 3.11 of th the e case of an an air bubble An illustration present in th the e cath catheter eter or tubing in which the air bubble acts like another capacitor in the equivalent circuit. —
Vi
V~= blood pressure waveform L~= inertance of catheter and tubing = resistance of catheter and tubing = capacitance of transducer transducer V = output waveform 0 = capacitance of bubble
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Spacelabs Medical: BLOOD PRESSURE
A discrete air bubble or multiple microbubbles, when present in the catheter or tubing, acts as another capacitor in the equivalent circuit (Figure (Figure 3.11). 3.11). This value of of C,~, This increases the value C,~,thereby thereby lowering cot, and raising / /33 (Figure 3.12). T he resulting waveform may be drastically overdamped and and lack lack some of th the e high frequency components of th thee original signal (Figure 3.9, overdamped). In cases in whic hich h the monitored waveform naturally lacks the high frequency components, an air bubble may not result in any appreciable degradation of the the signal. Since signal. Since most peripheral arterial pressure waveforms waveforms are are gener gener-ally lacking ally lacking in in high frequency components, as discussed in Section 2.5.1, small 2.5.1, small air bubbles usually have little effect thee effect on on the quality of th waveform. The damping effects of air a ir bubb bubbles les becom becomee more evident in central arterial pressure waveforms that contain relatively more high frequency components. dampingof a pressure measurement system may Clinically, the dampingof a pressure measurement be determined by means of a “snap test’~which provides a reasonable approximation of the step response. A bag of fluid under about to a a fast flush valve that opens the 3000 mm H g pressure is connected to 30 the e transducer to th the e 30 0 mm Hg and then suddenly then suddenly tubing near th closes, close s, there thereby by approximating a pressure step (Figure 3.14). The signal is the same general form as the response of th the e transducer signal previously discussed bal balloo loon n tes testt response, but is but is superimposed on the blo blood od pressure waveform (Figure 313). 313). By By performing a snap test the e damping ratio can and adjusting the the variable variable resistance device, th be optimized. The pressure bag and valve are standard components of hospital pressure monitoring systems.
61
Figu Figure re 3.1 3.12—A 2—A representation of th the e frequency response of asystem with an air bubble in th the ecath catheter eter or tubing. Such a bubble wifi increase th the e value of th the e capacitance of the the transducer (Cr), thereby lowering th the e natural fre and d raising the damping ratio (j3). quency (coo) an
91 Hz
W
/ 30= 0.033
10
—
W~=22 Hz / /33 = 0.137
1.0
—
-u a
No bubble
0.1
—
0.01
—
Bubbi
I
0.01.
I
I
0.02 0. 0.04 04 0.06 0.06 0.1
I
I
0.22 0.4 0.6
Relative Frequency
I
1
(-~)
I
2
I
III
4 6810
62
ystem m 3.2.2 Constant Infusion S yste A constant infusion catheter infusion catheter flush device is commonly used when
monitoring direct bloo blood d pressu pressures res for several hours such as during and after surgery or for several days as in the intensive care unit (ICU). Such a device maintains continued catheter patency by preventing coagulation of blood in the indwelling catheter. A typical constantflow device includes a fluid source under pressure, a valve that allows infusion of approximately fluid per hour, and a approximately 3 milliliters of fluid dome fo forr attachment of a strain gauge transducer (Figure 3.14). This arrangement connects to th thee previously introduced catheter by by rigid rigidwalled clear tubing. one e to T he flush solution (usually 0.9% saline solution with on two tw o unit unitss of aqueou aqueouss hep hepari arin n per milliliter of fl flui uid d added to prevent is pressurized pressurized approximately 3 0 0 mm Hg by using coagulation) is a standard intravenous fluid pressure ba bag. The continuous flush action is achieved by employing the large resistance in the constant flush valve to convert the pressure source into a flow source. The also incorporates fast-flush feature constant flush valve also incorporates a fast-flush feature that can be used to fill the transducer dome and tubing o orr t too clear blood from the system. The fast flush is commonly activated by either pressing a spring-loaded lever or pulling an elastic cord (depending upon device), which open openss a valve in the flush device. When the lever o orr cord is released, the valve snaps back t too the closed position to prevent inadvertent infusion of large large volumes of fluid. fluid. The fast flush
. ~
forr dynamic testing valve may also be used to input square waves fo of the catheter system (See Section 3.2.1).
64
3 .3 Intravascular(Catheter-tip) Transducer Systems S ystems The problems inherent in the combination of a a fluid-filled catheter and an exter externally nally locat located ed transd transduce ucerr can be avoi avoided ded by plac placing ing a sma small ll The potential transducer near the tip of the catheter. The potential distortive effects of the fluid column and and tubing tubing between the pressure source and By locating locating the transducer in a side transducer are thus eliminated. By port configuration in the catheter, kinetic energy distortion does not occur. The frequency response of such such an intravascular transducer system is essentially the frequency response of the the transducer itself. Drawbacks to current catheter-tip transducers inclu include de pro prohibit hibitive ive cost Mikro-Tip trans and fragility Figure 3.15 Figure 3.15 presents a diagram of a Millar Mikro-Tip transducer (Mifiar Instruments, Inc., Houston, Texas), the most well range of of freque uency ncy range known of the catheter-tip transducers. The rated freq this device is 0 to 20,000 Hz and it is available with one or more sensors in sizes as small small as 3 French.
3 . 4 Blood Pressure Pressure Transducers Transducers Principles Principles 3.4.1 Principles o f O perat peration ion The Wheatstone bridge is the basic basic circuit circuit employed in most pressure transducers (Figure 3.16). If the values of all al l four resistors are exactly equal, exactly equal, the output voltage is zero. If the resistance of any of
the arms of the the bridge changes, the bridge becomes unbalanced and an output voltage is generated proportional to the change in resistance and the excitation voltage.
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Spacelabs Medical: BLOOD PRESSURE
Nearly all commonly used pressure transducers are strain gauges, which operate on the principle that the resistance of of certain certain range of applied materia mat erials ls chan changes ges linear linearly ly ove overr a certain range applied strain. In metal tal stra strain in gau gauge ge arran arrangeme gement, nt, one or more of the resisthe classic me five arms of a Wheatstone bridge is composed of a metal strand or foil that is either stretched or released from a pre-stretched state by applied pressure on a diaphragm (Figure 3.17). Metal strain gauges have been widely used in a variety of applications applications for decades. R Re ecently, however, semiconductor materials such as sificon have become gauge factor factor (change in resistmore common, du due e to their higher gauge ance/change in length) and potential for miniaturization. Figure 3.18 shows an arrangement in which the positive-doped the positive-doped (p-doped) silicon elements con elements of a Wheatstone bridge are diffused directly onto a base of negative-doped (n-doped) silicon (for a discussion of doping and semiconductor theory see references 8 to to 10). 10). Although semiconductor strain gauges are very sensitive to variations in temperature, the inclusion of eight elements to form all four resistive arms of a bridge eliminates this problem by exposing a ll of the elements to the same temperatures.
valuation on 3.4.2 Considerations in E valuati evaluating a transducer include freSome factors to consider when evaluating quency qu ency response, drift with time and temperature, and durability. The Th e relative importance of each factor depends upon the transducer’s
application. Most commercial transducers meet the basic requirements in terms of drift and frequency response. For most arterial blood bloo d press pressu ure monitoring, the frequency response of the transducer is not as important as might be thought, since the response of the the total system is determined lar largel gely y by the characteristics of the catheter and tubing rather than by those of the transducer.
69
The issue o durabifity has become more co more compl mplex ex as as t tradition raditional al of f durabifity reusable reusa ble transdu transducers cers are challenged by disposable transducers. Re for a is lifetime of several usable transducers designed to designed to operate years and are are quite quite are expensive. Damage, Dam age, which common in the equipment-hostile setting of the the ICU, can reduce the lifetime and accuracy of reusuable reusuable transdu transducers, cers, thus increasing their cost per patient. Disposable transducers, recently introduced by several manufacturers, are designed for single-patient use in a hospital, after which they are discarded along with the tubing, stopcocks, and catheter.
3.5 Measurement Erro Errors, rs,
Distortions, a n d Artifacts Artifacts 3.5.1 E n d P ressur ressure, e, C at atheter heter W W hi hip, p, Catheter Impact Arti rtifacts facts a n d Catheter Impact A When pressure i iss measured in the pulmonary artery, the aorta and measurement nt can occur du due e the ventricles, certain distortions of the measureme locations. Catheter whip arises arises frequently frequently tohigh blood flow in those those locations. in the pulmonary artery. Acceleration of the fluid in the catheter by the th e whipping mot motion ion of the catheter t tip ip in the high velocity stream 1 0 mm Hg (Figure 3.19). can result in superimposed waves of ± tip p of the catheter is Catheter impact, which happens which happens when the ti propelled into the rapidly moving valve leaflets or th the e vessel walls, to occur occur in the waveform. Both causes high frequency transients to catheter whip and catheter impa impact ct are difficult to prevent and, to a certain certai n extent, must be accepted in the clinical situation. clinical situation.
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SpaceLabs Medical: BLOOD PRESSURE
Figui~e3.18 3 .18
—
Illustrations of diff diffused usedp-type p-type strain gau gauge. ge.
Clamp
—
n-type Si plane
Silicon
P
1
— (c)
T 2
Q2
Si
R
2
P
2
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Spacelabs Med Medical: ical: BLOOD PRESSURE
another type of transducer distortion, End pressure artifact, another type results from placing an end-hole catheter facing into a high flow occurs left stream. This measuring pressures the partially aortaally c when inthat and ventricle. Flowing bloo bl ood d posse possesses sses kinetic energy ener gy parti co onverts to pressure when the blood suddenly comes to a stop. Since any measu measured red bloo blood d pressure (total pressure) represents the sum of the hydrostatic, kinetic and lateral components, placing an end-hole catheter facing upstream leads to an elevated pressure measurement. this rea reason son,, catheters intended for pressure measurement in the For this For aorta and left ventricle are manufactured with multiple side ports instead of an end hole. This configuration ne negat gates es th the e kinetic energy component and measures measures the lateral and hydrostatic pressures.
E ff ffects ects
The e changes in intrathoracic pressure associated with breathing affect Respiratory 3.5.2 Th
both central and peripheral peripheral blood pressu pressure re measurements. In central pressure measurement measurements, s, especially pulmonary artery measurements, both systolic and diastolic pressures vary phasically with expiration as a direct result of the pressure changes inspiration and expiration to move move air into and out of the the lungs (Figure in the chest required to 3.20). Th The e least biased estimate of pulmonary pulmonary artery and other central pressures occurs occurs at at end expiration, when intrathoracic pressure approximates atmospheric pressure. This is true for both normal and mechanical positive pressure ventilation. is not arteries, peripheral blood pressu ssure re variation due directlyIntothe changes chest pre but rather to rather to the pressure in the cavity, effects of those changes on left ventricular stroke volume as dictated by the venous return. Normal, spontaneous respiration augments venous return during inspiration, whereas mechanical, controlled positive pressure ventilation reduces venous return during inspiration. This large variations may produce large variations in peak systolic systolic pressure while d iastoli iastolicc peak-to-to-peak peak varpressure changes little (Figure 3.21). Normally, this peak iation should be less than 1 0 mm Hg. In some disease states this varHg.. In the peripheral arteries, iation may be as high as 5 5 mm Hg therefore, the best estimate of true pressure i s the average of a ll beats
therefore, the best estimate estimate of of true pressure i iss the average of a a ll beats 11 over a representative respiratory cycle.
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Figure 3.20 The effect of airway airway pressure on pulmopulmonary artery nary artery pressure. —
a) The effect of normal, spontaneous spontaneous respirations respirations on the th e pulmonary artery pressure waveform. b) The effe effect ct of positive positive pressure, mechanical ventilation on th the e pulmonary pulmonary artery pressure waveform. artery pressure
See text for discussion.
Pulmonary artery pressure
(a)
Alveolar pressure (estimate)
Pulmonary artery pressure
(b)
Alveolar
pressure (estimate)
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~~SpaceLabs
Figure 3.21— Figure 3.21— The effect of airway of airway pressu pressure re on peripher peripher-al arterial pressure. a) The effect of normal, spontaneo spontaneous us respira respirations tions on the peripheral arterial pressure waveform. b) The effect of positive pressure, pressure, mechan mechanical ical ventilation on th the e peripheral arterial pressure waveform.
See text for discussion.
Systemic (a) arterial
pressure
Systemic (b ) arterial pressure
Medical: BLOOD PRESSURE
75
3.5.3 Transducer Zeroing T o ensure accurate measurements, the transducer must be zeroed before any pressure monitoring. T o zero the transducer, the monitor must measure atmospheric pressure by opening a stopcock or or “zero port”~T o avoid avoid errors errors du to hydrostatic hydrostatic pressure, it is essen is essen-due e to same horizontal level as the tip tial to position the zero port at the the same of the the catheter (reference level). It is not necessary to have the trans reference level level since since modern pressure amplifiducer exactly ducer exactly at the reference ers incorporate a zeroing system which can bal balanc ance e out a significant offset. As long as the relationship between the amount o of f transducer offset. reference level level arid arid the transducer transducer remains after er zeroi zeroing, ng, the remains constant aft pressures will be registered accurately Consequently, registered accurately Consequently, if the zero port is below the reference level (that i is, s, the catheter tip) when zeroing level moves moves up after zeroing, the measured presor if the reference level sure will be 2 mm Hg high for each inch of offset (the weight of a 1 inch column of saline saline solution). Conversely, the pressures will be 2 mm Hg low for each inch that the zero port i iss above the reference level. This offset is not of great great co conc ncern ern when monitoring systemic arterial pressures of 8 8 0 to 20 2000 mm Hg, bu butt becomes highly significant when measuring central pressures such as pulmonary capfflary (Figure 3.22). 3.22). Ideally, wedge pressure that averages about 5 mm Hg (Figure pressure that a ll blood blood pressure measuremen measurements ts shou should ld be perfo performe rmed d with the (phie-catheter tip and zero port positioned at the level of the the atria (phie bostatic axis).
4 .0 NO NI NINVA NVA SIVE ( I ND I RE CT) TECHNIQU QU ES M E A S U R E M E N T TECHNI 4 .1 AuscultatoryMeasurement The noninvasive, or indirect, measurement is the most indirect, blood blood pressure pressure measurement common method for assessing a person’s pressure status. The au aus scultatory technique employs the familiar pressure cuff, hand pump, manometer, and stethesco stethescope. pe. Th The e com complete plete device, known as a
sphygmomanometer, uses a pneumatic cuff enciimling enciimling the upper arm,
indicate and pressure gauge pressure in the cuff. aManometers are (manometer) of tw is two o types: to aneroid, aneroid , in the which pressure measured by a mechanical transducer transducer and displayed on a dial, and mercury mercu ry in which pressure pressure elevates a column of mercury mercury in a cali-
76
brated glass tube. Since an anero aneroid id mano manometer meter is a spring-loaded mechanical device, mechanical device, it m may ay beco become me inaccurate with frequent use and therefore must be regularly calibrated with a mercury manometer. In practice, practice, the pneumatic cuff is applied to the upper arm and pumped up to a pressure greater than the systolic blood blood pressure pressure in the underlying lar large ge brac brachial hial artery. Th The e cuff pressure pressure collapses the artery a and nd stops blood flow to the lower arm. The pressure in the cuff is gradually released through the valve in the hand pump. When the cuff pressure pressure drops slightly below systolic arterial pressure blood begins begins to to spurt through the partially compr compressed essed segment of the brachial artery producing arterial sounds (Figure (Figure 4JA). 4JA).
4.1.1 Korotkoff Sounds The spurting blood from the compressed brachial artery produces The turbulence and vibrations within the vessel which create noises known as Korotkoff sounds. sounds. The stethoscope, when placed on the just st distal to the cuff, detects these Korotarm over the brachial artery ju koff sounds. sounds. As the cuff pressure pressure decreases, the Korotkoff sounds sounds finally disappear with restoration of laminar flow of blood blood in the brachial artery (Figure 4.1B). Five phases of Korot Korotkoff koff sounds are commonly heard during cuff deflation (Table 4.1). While the onset of the Korotkoff sounds sounds (phase I) is the accepted point for systolic systolic pressure, pressure, the d iastoli iastolicc pres pres- the d sure endpoint has been subject to controversy over the years. In 1967, Association (AHA) (AHA) advised that the pressure the American Heart Association at muffling o the sounds (phase (phase 1 1 V ) be considered the the d d iastoli iastolicc pres pres- of f the sure~In its latest recommendations published in 1 9 8 1 , the the Al-IA specified the use of the point of cessation cessation of Korotkoff Korotkoff sounds sounds (phase diastolic olic pressure except in those individuals in whom the V) as diast sounds continue to 0 mm Hg Hg,, in whi hich ch case phase IV should be in2 terpreted as diastolic pressur& The lack of phase V is associated with o f phase certain diseases and i iss also a naturally occurring phenomenon during vigorous exercise. The AHA’s reasoning for this revised specifi-
cation is that the absence of sound less subjective sound (phase V V)) is less subjective than (phase IV the muffling of sound (phase IV ) and therefore should provide more consistent data for epidemiological purposes.
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Medical: BLOOD PRESSURE
T A B L E
4 .1 The Five Phases of Korotkoff Sounds Sounds in Indirect Blood Pressure Measurement
Phase I .
Phase II.
-
-
Phase ifi.
-
Phase IV .
Phase V .
-
-
The The first sounds detectable when the falling cuff cuff pres pres-sure is slightly below the systolic pressure. These sounds are soft at the start, then they rapidly increase in intensity. They are detected over a range of 1 0 to 1 5 mm Hg as the cuff is is deflated. Systolic pressure i iss be the Korotk otkoff off considered to be the level at which phase I Kor are initially initially heard. sounds are This phase begins when a murmur-like sound occurs. These sounds may quickly fade and occasionally may transiently und undetectable etectable as the cuff pressure be transiently creating may gap peridecreases, an ‘auscultatory an ‘auscultatory silent is or cuff od.. The examiner od miss this gap if the the i speri notsufficiently inflated to obliterate obliterate the pulses. This This could the pulses. The e result in a falsely low systolic pressure reading. Th phase II Korotkoff sounds is 1 5 to pressure range of phase 20 mm Hg. The Korotkoff sounds sounds take on a ‘thumping’ quality and are at their loudest. The pitch and intensity of the sounds change abrupt occurs at ly , taking on a muffled tone. This typically typically occurs a slightly higher arterial pressure than true diastolic
pressure. As thee cuff th cuff pressu pressure re continu continues es to decrease, decrease, the the sounds disappear completely. The point of disappearance of the sounds is phase V , which usually occurs at a level slightly below true intravascular diastolic pressure.
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ources ces o f E rr rror or 4.1.2 Limitations a n d S our is simple simple The auscultatory technique for measuring blood pressure is is sub equipment. However, this42 and uses a minimum of equipment. method 421 1 ject to a number of of limitations limitations and sources of error.’ Obtaining an accurate auscultatory blood pressure is difficult in a noisy environThe e operator must acuity for low frement. Th operator must possess good hearing acuity also often often fails quency sounds (2 (200 to 30 3000 Hz). Auscultatory technique also to give give accurate pressures for for infants infants and hypotensive patients (for example, those experiencing shock). auscultato ltatory ry method method,, altho althoug ugh h less technologically The auscu monitoring, requires demanding than invasive blood pressure monitoring, requires attention to details of technique technique (Figure 4.2). The correct size of the the oc accurate bloo clusive cuff is crucial to obtain accurate blood d pressur pressure e readings (Table 4.2). Use of an 4.2). an incorrect cuff size can produce a falsely high or low reading (Figure 4.3). In general, undersized undersized or or loosely applied cuffs wifi overestimate, and oversized cuffs underestimate underestimate the true true auscultatory blood pressure. The AH AHA A has recom recommend mended ed that the width of the the air bladder inside the cuff equal equal 4 0% of the the circumference circumference of the limb on which it is placed and the length of the bladder be approximately proxim ately tw twice ice the recommended width (that is, bladder bladder length length equal to 80 equal 80% % of arm circumference). TABLE 4 .2 Recommended Sphygmomanometer Cuff Sizes
Arm Circumference (mid-arm) (cm)
Cuff Name Name Newborn
5 7. 7.55 -
Infant
7.55 1 3 7.
Child
13-20
Small Adult
-
1 7 2 6 -
Bladder Width (cm)
Bladder Length (cm)
3
5
5
8
8
13
11
17
Adult Large Adult Thigh
24 2 6
-
32 -
42
42-50
13
17 20
24
32 42
Adapted from: American Heart Association. Association. Recommendations for human blood pressure determination by sphygmomanometers. Stroke 12:555A-564A, 1981.
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Figure 4.2 A schematic of the sources of error in auscultatory blood pressure measurement. —
Measurement errors
Observer
Causing
Instrument
systematic
Causing random
errors
errors
• Prejudice fo for r “normal” readings • Round-off error
• Inaccurate Sphygmomanometer (eg., zero error error,, tilting tilting,, dirty tube, etc.) • Cuff width and length
• Mental concentration • Hearing acuity Confusion of auditory an and d
visual cues visual Interpretation of sounds High ambient noise level • Rates of inflation and
deflation
True variations in blood pressure
Unknown factors
Known factors
• Recent physical activity
Emotional state and d arm • Position of subject subject an
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Failure to pro proper perly ly place the head of the the stethoscope directly cause Korotkoff Korotkoff sounds of low intensity, low intensity, over the brachial artery can cause
leading to erroneous pressure readings. Also, excessive application persistance of of Korotkoff pressure may produce a persistance Korotkoff sounds, sounds, which may result in a gross underestimate of diastolic pressure. The AH AHA A recom the stethoscope rather than the more commends that the bell of the monly employed diaphragm be used to measure blood pressure (Figure 4.4). Another potential problem with the auscultatory method is the phenomenon of the auscultatory gap. This period of silence silence during the second phase of the the Korotkoff sounds may cause the observer to underestimate the systolic pressure by as much as 1 0 0 mm Hg. the systolic Such an error error can be avoided by ensuring that the occluding cuff is is quickly inflated to a point approximately 2 200 mm Hg above the the obeither the the brachial brachial or radi literation of either radial al pu pulse lse as determined by palpation of the radial radial or or brachial artery. The auscu auscultatory ltatory gap generally occurs in hypertensive patients and can result in failure to to detect detect severe hypertension in some individuals. of the auscultatory technique relates to the limitation of Another limitation fact that this method does not provide a measurement of me mean an blo blood od pressure. Mean pressu pressure re may be estimated using the formula given in Section 1.3, though the accuracy and precision of this estimate is subject to many potential variables. Despite its limitations, the auscultatory technique can provide accurate and repeatable blood pressure measurements in the hands of a skilled operator. operator. Du Due e to the naturally occurring minute by minute variations in blood pressure, several auscultatory measurements should be taken to obtain an accurate accurate profile profile of the the patient’s blood pressure.
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Non invasive ve Measurement Measurement 4.2 Automated Noninvasi easurement ement 4.2.1 Auscultatory M easur
Noninvasive blood pressure measurement can be automated by replacing the hand pump with an automatic pump that is activated for a single measurement or set to inflate the cuff periodically periodically at a predetermined interval. The blood pressure is measured by the auscultatory method, using a small microphone placed in the cuff to detect the Korotkoff sounds. sounds. A computerized program then deterdetermines the blood pressure measurement. With this instrumentation, the user must exercise care in applying the cuff so that the microphone lies directly over the brachial artery to ensure accurate sound detection.
easurement ement 4.2.2 Oscillometric M easur The automated oscifiometric method of noninvasive blo blood od pre pressu ssure re distinc istinctt advan advantages tages over the auscultatory method. measurement has d Since sound i iss not used to measure measure blood pressu pressure re in the oscillometric technique, metric technique, high environmental environmental noise noise levels such as tho those se fou found nd clinic or or emergency emergency room do no in a busy clinic nott hamper the measurement. In addition, because this technique does not require a microphone or transducer in the cuff, placement of the the cuff is not as critical as it is with the auscu auscultatory ltatory or Doppler methods. The oscifiometric method works without a significant loss in accuracy even when the cuff is placed placed over can over a light shirt sleeve. The appropriate sized cuff can be used on on the forearm, thigh, or calf, as well as in the traditional oscillometric method method location of the upper arm. A disadvantage of the oscillometric that excessive excessive movement or vibration during the meas is that measu ureme rement nt can cause inaccurate readings or failure to obtain any reading at all, as is true of the the auscultatory method as well.
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Spacelabs Medic Medical: al: BLOOD PRESSURE
The oscifiometric technique technique operates on the operates on the principle that as an occluding cuff deflates deflates from a level above systolic systolic pressure, pressure, the artery walls begin to to vibrate vibrate or oscillate as the blood flows turbulently vibrations will will through the partially occlu occluded ded arter artery y and that these vibrations be sensed in the transdu transducer cer system monitoring cuff pressure. As the pressure in the cuff further further decreases, the oscifiations increase to a fully deflates maximum amplitude and then decrease until the cuff fully the e po poin intt of and blood flow returns to normal. The cuff pressure pressure at th maximum oscifiations usually corresponds to the mean arterial pressure. The point above mean pressure at which the oscifiations begin to rapidly increase in amplitude correlates correlates to the systolic pressure; and the point below the maximum at which the oscifiations begin to rapidly decrease in amplitude correlates with diastolic pressure (Figure 4.5) ~224 These correlations have been derived and proven empirically but are not yet well explained by any physiologic physiologic theory. theory. The actual determination of bloodpressu blood pressure re by an oscillometric device is performed by a proprietary algorithm developed by the manufacturer of the the device.
easurement ement 4.2.3 Doppler Ultrasound M easur The Dopp two o piezoelectric crystals Doppler ler ul ultrasou trasound nd method employs tw of the located between the occluding cuff and and the surface surface of the arm. One crystal generates ultrasonic waves (about 8 MHz) that are directed 5 at the arm surface over the brachial artery~ The other crystal receives reflected by by the art the waves reflected artery ery and surrounding tissues. if the reflecting surfaces are are stationary, stationary, then the signal i iss reflected without change in frequency. However, i if f the the artery wall is in motion when it reflects reflects the ultrasonic waves, the signal returning to the receiving crystal shifts crystal shifts in frequency according to the Doppler effect. Th This is shi shift ft in frequency (Af) can be amplified and heard by an observer o orr see seen n on a display.
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In the normal, uncompressed brachial artery laminar flow produces little or no movement of the artery wall. In the completely compressed artery no movement of the wall occurs. However, when the occluding cuff is is inflated to a level between systolic and diastolic pressures, blood spurts blood spurts through the artery when arterial pressure exceeds cuff pressure. pressure. As the artery opens and closes, the moving arterial arter ial wall wall causes causes a a Doppler shift of the incident ultrasound signal. Therefore, as the cuff is deflated from above systolic to below diastolic pressure, clicking sounds will appear then disappear in a fashion similar to the auscultatory method (Figure 4.6). Due Du e to the extreme dependence of Doppler ultrasound meas meas-precise se placement placement of the urement of blood pressure on preci the cuff and transducer, it is generally used only in cases where the auscultatory method fails. Such circumst circumstances ances indude an extremely noisy environment such as in a helicopter during transport, and for measurements on ir~fantsarid arid persons in shock. Th The e Doppler ultraso ultrasound und technique can be used in more noisy environments than the auscultatory method because method 200 00 Hz Hz,, because the change in frequency i iss usually above 2 Hz,, a range to whereas the Korotkoff sounds are mostly below 20 2000 Hz human ear is less sensitive~ which the the human
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4.2.4 Non i nvasive C onti ontinuous nuous Finger onitoring ing Blood Pressure M onitor A recently developed developed variation variation of the the oscifiometric method employs small ll fin finger ger cuff cuff that detects a photoplethysmograph located inside a sma changes in blood volume under the cuff based based on changes in the amount of light light transmitted through the finger. When the cuff is inflated to a point near mean arterial pressure, pressure, the output of the plethysmograph varies plethysmograph varies directly with changes in blood volume, which directly relates to the desi desired red parameter, blood pressure. In the servo control system controls controls cuff cuff method first proposed by Penaz, a servo control pressure to mainta maintain in con constan stantt blood volume in the finger (Figure 4.7). The Th e servo system is driven by a feedback circuit from the output of plethysmograph. Provided servo system servo system rapidly thatthe react the the pressure to track arteriall cuff be enough pressure, in thecan should should the same at a ll times as the pressure in the finger artery.2 6 ’ 2 7 This method provides accurate results in resting and anesthetized patients, but, du due e to a very high sensitivity to movement and vasoconstrictive state state of the finger, transient changes in the vasoconstrictive the finger, its usefulness in the ICU or ambulatory setting has not been established.
4.3 Correlation Between D Dir iree c t
a n d Indirect Indirect Measurements
Clinicians have long noted that direct blood pressure measurements do no measurements. ents. This This should not nott always correlate with indirect measurem be su surprisi rprising ng because of the different different principles underlying the various methods. The direct method measures blood pressure, while indirect techniques correlate pressure in an occlusive cuff with phenomena related to bl bloo ood d flow. Since flow is only one of many blood pressure, it follows that the direct measuredeterminants of blood ment may respond to factors independent of blood blood flow and thus two o methods even when proper produce a discrepancy betw between een the tw technique is used and equipment is well maintained. One can usually
technique is used and equipment is well One can usually predict the direction, but not the amount, of such predict such a discrepancy.
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Generally, indirect methods of blood blood pressure measurement pressure measurement underestimate direct systolic systolic pressure pressure by 0 to 5 0 mm Hg. This inconsistency is du sistency due e partially to the normal physiologic pulse wave distortionmechanisms tortion mechanisms discussed discussed in Section 2.5. With respect to diastolic accuracy of of indirect indirect methods will var pressure, the accuracy vary y depe dependi nding ng on technique and algorithm us the technique the used. ed. Using Using the standard auscultatory method (Korotkoff method), method), phase IV slightly overestimates and direct diastolic measurement. phase V slightly underestimates the direct diastolic to mimic mimic Most automated indirect blood pressure devices attempt to the auscultatory method and correlate their diastolic measurement with auscultatory phase V , which may underestimate direct diastolic pressure. These differences between direct and indirect blood pressure individuals. Certain Certain normeasurements are to be expected in normal individuals. mal and abnormal physiologic conditions can increase the variation. For example, in persons with extreme hypotension and increased peripheral resistance (shock), indirect methods, especially the auscultatory technique, can fail completely due due to the profoundly decreased blood flow, which occurs in such circumstances. In contrast, the high flow rate and decreased peripheral resistance seen dur sounds to ing exercise and in some diseases can cause Korotkoff sounds ing Hg,, confounding confounding those continue to 0 mm Hg those indirect methods that use phase V as the diastolic endpoint. It should be emphasized th that at an any y auscultatory estimate of blood bloodpressu pressure re may overestimate or underestimate the corresponding direct direct (invasive) (invasive) value value depending upon a multitude of factors, many of which which are poorly understood or not recognized. the indirect methods in use today, only the oscffloFinally, of the metric methods give a tru true e measu measurement rement of mean mean arterial pressure. The other other indirect indirect methods rely on a ca calc lcul ulat ated ed es esti tima mate te of mean pres pres-sure which can be as much as 3 0 mm Hg from the true mean arterial pressure.
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5.0 5. 0 REFERENCES 1. Guyton AC : Textbook of Medical Medical Physiology. Seventh Edition. Philadelphia: WB Saunders Company, 1986. Transform. 2. Brigham FO: The Fast Fast Fourier Fourier Transform. Englewood Cliffs, New Jersey: Prentice-Hall, Inc., 1974. 3. Krovetz U, Goldbloom S : Frequency content of intravascular and intraca intracardiac rdiac pressur pressures es and IEEE Trans Biomed their time derivatives. IEEE Trans Biomed Eng BME-21:498-501, 1974. 4. Milnor W 4. Milnor W R: Principles of Hemodynamics. Hemodynamics. In: Mountcastle VB (Ed): Medical Physiology. Twelfth Edition. S t . Louis: C . V . Mosby Company, 1968. 5. O’Rourke M F, Yaginuma T : Wave reflections Wave reflections and the th e arterial pulse. Arch m t Med 144:366-371,
17 . Roberts LN, Smiley JR . Manning GW: A of direct direct and indirect blood comparison of
6. Yang1984. SS, Bentivoglio Bentivoglio LG, Maranhao V , et al.: From Cardiac Catheterization Data Data t too Hemodynamic Parameters. Third Edition. Philadelphia: F.A. Davis Comp Company, any, 1988. 7 . Webster JG Webster JG (Ed): Medical Instrumentation: Application an and d Design. Boston: Houghton Mifflin Company, 1978. 8. Senturia SD, Wedlock BD : Electronic Circuits and Applications. New York: York: John John Wile Wiley y and Sons, 1975 . 9. Miiman J: Microelectronics: Digital and Analog Circuits an and d Systems. New York: McGraw-Hill, 1979. Inc., 1979. Inc., 10 . Boylestad R , Nashelsky L : Electronic Devices an and d Circuit Theory. Circuit Theory. Third Edition. Englewood Englewood Cliffs, Cliffs, New Jersey: Prentice-Hall, Inc., 1982. 11 . Ellis DM: interpretation of beat beat to beat blood
arterial measuring blood pressure, part III. Med 1981. Inst 15:182-188, 22. Mauck G G W, Smith CR CR,, Geddes LA , et al.: The maximum oscillations meaning of the the point of maximum in cuff pressure pressure in the indirect measurement of blood pressure, Part I I. Trans ASME J Biomech Eng 102:28-33, 1980 . 23. Geddes LA , Voelz M, Combs C, et al.: Characterization of the the oscillometric method for measuring indirect blood pressure. Ann Biomed Eng 10:271-280, 10:271-280, 1982. 1982. 24. Geddes LA : Cardiovascular Devices an and d Their Applications. New York: John Wiley and Sons, Inc., 1984. 25 . Stegall H F, Kardon M Kardon M B , Kemmerer WT: Indirect of arterial blood pressure by measurement of blood pressure ultrasonic sphygmomanometry. J Appi Doppler ultrasonic Physiol 25:793-798, 1968. 26 . Yamakoshi K, K, Kamiya A, Shimazu H, et al.: Noninvasive automatic monitoring of instantaneous arterial blood pressure the e blood pressure using th vascular unloading technique. Med Biol Eng Comput 21:557-565, 1983. 2 7. Wesseling Wesseling KH, Settels I I, DeWit B : The measurement of continuous finger arterial pressure noninvasively in stationary subjects. In: Schmidt TH, Dembroski TM, Blumchen G (Eds). Biological and Physical Physical Factors Factors in Cardiovascular Disease. Berlin: Disease. Berlin: Springer Verlag, 1986.
ventilatory pressure values in the presence of ventilatory changes. J Clin Monit 1:65-70, 1985 . 12. American Heart Association: Recommendations for human blood pressure blood pressure determination determination by sphygmomanometers. Circulation 36:980, 1967. 13 . American Heart Association: Recommendations for human blood pressure determination by sphygmomanometers. Stroke 12:555A-564A, 1981. 14 . Hamilton WF, Woodbury RA, Harper H T: Physiologic relationships between relationships between intrathoracic, intraspinal and arterial pressures. JAMA 107:853-856, 1936.
pressure determinations. Circulation 8:232-242, 1953. 18 . Van Van Bergen Bergen FH, Weatherhead S . Treloar AE, Treloar AE, et al.: Comparison of indirect an and d direct methods of measuring arterial blood pressure. Circulation 10:481-490, 1954. 10:481-490, 1 19 . Holland W N , Humerfelt S Humerfelt S : Measurement of blood blood Comparison pressure: of intra-arterial and cuff values. Br Med J 2:1241-1243, 1964. 2 0 . Raftery EF , Ward AP : The indirect method of recording blood pressure. Cardiovas Cardiovas Res Res 2 : 2 1 0 - 2 1 8 , 1 9 68 .
Bruner JMIR, Krenis L I, Kunsman, JM , et al.: 21. Bruner JMIR, Comparison of direct and indirect methods of
15 . Ragan C , Bordley J: The accuracy of clinical measurements of arterial arterial blood pressure, wi with th a note on th the e auscultatory gap. Bull Johns Bull Johns Hopkins Hosp 69:504-528, 1941. 16 . Steele T Steele T M : Comparison indirect of simultaneous (intra-arterial) (auscultatory) an and d direct arterial pressure in man. measurements of arterial Mount Sinai Hosp 8:1042-1050, 1941.
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6.0 ILLUSTRATION CREDITS Figure 1.7 of Medical Medical PhysiolAdapted from Guyton AC : Textbook of ogy; Seventh Editi Edition. on. Philadelphia, Philadelphia, W B Saunders Company, 1986. Figure 2.1 WR:: Cardiovascular System. In Mountcastle VB Minor WR (Ed.): Textbook of (Ed.): of Medical Physiology; Seventh Edition. St. Louis, The C . V. Mosby Co., Mosby Co., 1986.
Figure 2.2 Mendel D: A Practice of of Cardiac Cardiac Catheterization; Second Edition. Oxford, England, Blackwell Scientific Publications, 1974. Figure 2,4 Little RC: Physiology Physiologyof of the Heart rtand and Circulation; Third Edition. Chicago, Year Book Medical Medical Publishers Inc., Inc., 1985 1985 . Figure 2,SA Figure O’Rourke ME , TaylorMG: TaylorMG: Vascular Vascular Impedance. Circulation Res 18:126-139, 1966. Figure 2.5B Figure Adapted Adapt ed from O’Rourke M F, Avolio AP: Ascending Aortic Impedance as th the e Load Presented to th the e Left Ventricle: Effects of Effects of Change in Mean Pressure, Arter Arterial ial Com Complian pliance ce and Peripheral Resistence. In: Baumann D (Ed.): Les Alpha Bloquants. Paris, Masson S.A., 1981.
Figure 3.12 Webster JG (Ed.): (Ed.): Medical Medical Instrumentation: Application and Design Design.. Boston Boston,, Houghton Mifflin Co., 1 9 7 8 . Figure 3.17 Strong P: Biophysical Measurements; First Edition. Beaverton, Oregon, Tektronix, Inc., 1970 .
Figure 3.18 Cobbold RSC: Transducers for Medical Measurement: Wiley and Application and Design. New York, John Wiley an d Sons, Inc., 1974. Figure 3.19 and d Adapted from Geddes LA: Cardiovascular Devices an Their Applications. New York, York, John John Wiley and Sons, Inc., 1984. Figure 3.22 Shulze SE : Pressure Monitoring Instruments for Critical Care: Theory an and d Applications. Chatsworth, Califomia, SpaceLebs Inc., 1976. Inc., 1976.
Figure 4.2 from: Rose Rose GA, Holland WW Crowley EA: A Adapted from: Epidemiologists. ists. London, The Sphygmomanometer for Epidemiolog Lancet 1:296-300 1:296-300,, 1964.
Figure 2 2.7 .7 Little R C: Physiology of the Heart artand andCirculation; Third the He Edition. Chicago, Year Book Medical Publishers, Medical Publishers, Inc., 1985.
Figure 4.3A Errorin Geddes LA , Whistler S J: The Error in Indirect Blood Pressure Measurement sure Cuff. Am Measurement with the Incorrect Size of Cuff. Heart J 96:4-8, 1978.
Figure 3.1 Textbook of Advanced American Heart Association: Textbook
Figure 4.3B Rushmer RE : Cardiovascular Dynamics; Fo Fourth urth Edition Edition..
Cardiac Life Support. Dallas, American Heart Association, 1987.
Philadelphia, WB Saunders Company, 1976.
Figure 3.5 Shulze S E: Pressure Monitoring Instruments for Critical Care: Theory and Applications. Chatsworth, Califomia, SpaceLabs Inc., Inc., 1976. Figure 3 .6 Yang S5, Bentivoglio L G, Maranhao V , et al.: Yang S5, al.: From Cardiac Catheterization Data to Hemodynamic Parameters; Third Edition. Philadelphia, FA Davis Company, 12 78. Figure 3.8
Figure 4.5 Figure Geddes LA: Cardiovascu Cardiovascular lar Devices and Their Application. New York, John Wiley and Sons, Inc., 1984. Figure 4.6 Figure Stegall H F, Kardon MB , Kemmerer WT: Indirect Measurement of of Arterial ArterialBlood Blood Pressure Pressure by by Doppler DopplerUlltrasonic Ulltrasonic Sphygomanometry. J Appl Physiol 25:793-798, Sphygomanometry. 25:793-798, 1968.
Figure 4.7 Schmidt TH, Dembroski TM, Blumchen G : Biological
Grossman W (Ed.): (Ed.): Card Cardiac iac Cathete Catheterizatio rization n and Angiography; Third Edition. Philadelphia, Lea & Febiger, 1986.
and Physical Physical Factors Factors in Cardiovascular Disease. Disease. Berlin, Springer Verlag, 1986.
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7 . 0 BIBLIOGRAPHY The following bibliography offers a chronological listing of citations citations pertinent to the study and determination of blood pressure blood pressure measurement. VASCULAR
IMPEDANCE, PULSE W A V E PROPOGATION, AND BLOOD FLOW
Hamilton WE Dow P : An experimental study of th the e standing waves in th the e pulse propagated through th the e aorta. Am J Physiol 125:48-59, 1939. Peterson L H: Th e dynamics of pulsatile blood flow. Circulation flow. Circulation Res 2:127-139, 1954. of f simul simulKroeker E J , Wood EH : Comparison o taneously recorded central and peripheral arterial pressure pulses during rest, exercise and tilted position in man. Circulation Res 3:623-632, 1955. Wiggers C: Wiggers C: Dynamic reactions induced by by compression of an Res 6:4-7, an artery. Circulation Res 1956. Van der Tweel L H : Some physi physical cal aspects of blood pressure, pulse wave, and blood blood pressure measurements. Am Heart J 53:4-17, 1957. Landowne M: A method using induced waves to study pressure propagation in human arteries. Circulation Res 5:594-601, 1957. Landowne M: Characteristics of impact and pulse wave propagation in brachial and radial arteries. J Appl Physiol 12:91-9Z 1958. Levy MN: Re lati lative ve influence of variations in arterial and venous pressures on resistance to flow. Am flow. Am J Physiol 192:164-170, 1958. Bergel DH DH,, Milnor WR : Pulmonary vascular impedance in in the the dog. Circulation Res 16:401-415, 1965. O’Rourke ME Taylor MG: Vascular impedance of the the femoral bed. Circulation Res 18:126-139, 1966. DH,, Bargainer Bargainer J J D: Hydraul Hydraul-Milnor WR , Bergel DH ic power associated with pulmonary blood flow and its relatio relation n to heart rate. Circulation Res 19:467-480, 1966. Taylor MG: MG: Use Use of of random excitation and spec-
O’Rourke M F, Blazek JV . Morreels CL, Krovetz U: Pressure wave transmission along the U: human aorta—changes with age and in ar degenerative disease. Circu Circulation lation Res terial degenerative terial 23:567-579, 1968. Roweil L B, Brengleman G L, Blackmon JR, Bruce RA , Murray TA : Disparities between aortic and peripheral pulse pressures induced by upright exercise an and d vasomotor Circulation 37:954-964, 37:954-964, changes in man. Circulation 1968. Remington JW O’Brien U: Construction of aor pressure pulse. tic flow pulse from pressure pulse. Am J Physiol 218:437-44Z 1970 . Influence uence of ventricular ejection O’Rourke M F: Infl on the relationship between central aortic and brachial pressure pulse in men. Cardi Cardi-ovasc Res 4:291-300, 1970. Milnor WR : Pulsatile blood flow. N EngI J Med 287:27-34, 1972. Westerhof N: Pressure an and d flow Elzinga G, Westerhof N: generatedby t the he left ventricle against different impedances. Circulation R es 32:178-186, 1973. C o x RH : Determinants of systemic systemic hydraulic power in unanesthetized dogs. Am J J Physiol Physiol 226:579-58Z 1974. cannula-Kim J JM M , Arakawa K, Bliss J : Arterial cannula factors in tion: factors in t he development of of ocdu ocdusion. Anesth Analg 54:836-841, 1975 . Westerhof N, V an den Bos GC, Westerhof N, Elzinga C, Sipkema F: Reflection in Reflection in t the he systemic arterial syst al system: em: effect effectss of aortic aortic and carotid occlusion. Cardiovasc Cardiovasc Res Res 10:565-573, 1976. Arts T , Kruger T I, V a n Gerven W, et al.: Propagation velocity and reflection of pressure waves i n the canine coronary artery. Am J Physiol 237:H469-H474, 192 9. Laskin JL, Paulus D, Bethea 1-IL: Pseudohypertension due to medial calcific sclerosis. J Am Dent Assoc 100:384-385, 1980.
tral analysis in the in the study of frequency dependent parameters of the the cardiovascular system. Circulation Res Res 18:585-595, 1966. Dick DE, Kendrick JE JE,, Matson GL, Rideout V Rideout V C : the he arterial Measurement o f nonlinearity nonlinearity in t system of the the dog by a new method. Circulation Res 22:101-111, 1968.
Murgo JP, Westerhof N, N, Giolma JP JP,, Altobelli SA : Aortic input impedance in normal man: relationship t o pressure wave forms. Circulation 62:105-116, 1980. Murgo JP Murgo JP , Westerhof N, N, Giolma JP , Altobeffi SA : Manipulation of ascending aortic presressure an and d flow wave reflections with t he vatsalva maneuver: maneuver: relationship to input impedance. Circulation 63:122-131, 1981.
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Stettler JC, Niederer P . Anliker M: Stettler JC, M: Theoretical Theoretical analysis of arterial arterial hemodynamics including the th e influence of bifurcations bifurcations Part I I:: Mat athe he- and d prediction of normal matical model an pulse patterns. Ann Biomed Eng 9:145-164, 1981. Stettler JC, Stettler JC, Niederer P , Anliker M, Casty M: Theoretical analysis of arterial hemodynamics including th the e influence of bifurcations Critical evaluation of theoretical Part I I: Critical evaluation theoretical model and comparison with noninvasive with noninvasive measurements of flow patterns in normal and pathological cases. Ann Biomed Eng Biomed Eng 9:165-175, 1981. Finkelstein S M, Collins V R: Vascular hemodynamic impedance measurement. Prog Cardiovasc Dis Cardiovasc Dis 24:401-418, 1982. Nichols WW Pepine C J: Left ventricular afterload and aortic input impedance: implications of pulsatile pulsatile blood flow. Prog Cardiovasc Dis Cardiovasc Dis 2 4:293-30 4:293-306, 6, 1982. Pepine CJ, Nichols WW: Aortic input impedance in cardiovascular disease. Prog Cardiovasc Dis Cardiovasc Dis 24:307-318, 1982. O’Rourke MF: O’Rourke MF: Vascular Vascular impedance in studies of arterial an and d cardiac function. Physiol Rev Physiol Rev 62:570-623, 1982. Wave reflections O’Rourke ME Yaginuma T : Wave reflections and the arterial pulse pulse.. Arch m t Med 144:366-371, 1984. Westerhof N, Sipkema P , et al.: Latham R D, Westerhof Regional wave travel an and d reflections along aorta: a study with six simulthe th e human aorta: taneous micromanometric pressures. Circulation 72:1257-1269 72:1257-1269,, 1985 . Little R C: Hemodynamics. in Physiology of the the Circulation Year Book Medical Heart He art and Circulation Year Book Medical Publishers, mc, Chicago:224-246, 1985 . P . Creenwald SE, DL, Sipkema Newman Westerhoff characteristics N: High frequency N: system. J Biomechanics of the the arterial system. 19:817-824, 1986. Berne R M, Levy MN: T he arterial system. In CV Mosby Mosby Co., Co., Cardiovascular Physiology, CV St. Louis, 1986, pp. 124-135. Asmar RG, Brunel PC, Pannier BM , et al.: Arterial distensibility Arterial and d ambulatory blood distensibility an pressure monitoring in essential hyperten hyperten-sion. Am J Cardiol 61:1066-1070, 198&
Chobanian A M Chairman 1988 Joint National Chobanian A Committee: The 1988 report of th the e join jointt national committee on detection, evaluation, and treatment of high high blood pressure. Arch m t Med 148:1023-1038, 1988.
B . Auscultatory Mudd SC, White PD: The auscultatory gap in sphygmomanometry. Arch m t Med 41:249-256, 1928. Berry MR: Berry MR: The mechanism and prevention of impairment of auscultatory sounds dining determination of blood pressure blood pressure standing patients. Staff Meetings Meetings of the the Mayo Clinic 9-702, Oct 30, 1940. Nuessle W WF: F: The importance of a tight blood pressure cuff. Am Heart J 52:905-907, 195 6. Rodbard 5, Chiesielski J : Duration of arterial arterial Cardiol 20:18-21, 1961. sounds. Am Am J Cardiol 20:18-21, Wilcox J : Observer factors in th the e measurement of blood pressure. Nursing Res 10:4-IZ 1961. Rose CA, Holland W W, Crowley EA: A sphygmomanometer for epidemiologists. [ancet 1:296-300, Feb 8,1964. Rose C: Standardisation of observers in bloodpressure measurement. pressure measurement. Lancet 1:673-674, 1965 . Ceddes LA, Hoff HE, and Badger A AS: S: Introduction of the auscu auscultatory ltatory method of measuring blood pressure—including a translation of Korotkoff’s Korotkoff’s original paper. Cardiovas Res Cardiovas Res Ctr Bull 5 :5 :5 7-74, 7-74, 1966. McCutcheon E P, Rushmer RF: Korotkoff sounds: an experimental critique. Circulation Res 20:149-161, 1967 Rodbard 5, Robbins AS : The components of sounds. ds. Am Heart J the Korotkoff soun 74:278-282, 1967. Eilersten E, Hummerfelt 5: The observer variation in th the e measurement of blood blood pressure. Acta Med Scand 184:145-157, 1968. Wright BM , Dore CF: A random-zero sphygmomanometer Lancet 1:337-338, 1970 . Perlman L V , Chiang BN, Keller J , Blackburn H: Accuracy of Accuracy of sphygmomanometers in hospital practice. Arch T nt Med 125:1000-1003, 1970 . IJr A, Cordon M: Origin of Korotkoff Korotkoff sounds. sounds. Am J Physiol 218:524-529, 1970 .
IL
BLOOD PRESSUR PRESSURE E MEASUREMENT
measurePanfiov B K : Auscultatory drop during measureNS Korotkoff’s Korotkoff’s ment of blood pressure blood pressure by NS method in patients with hypertension. Sovietskaia Meditsina 36(2):141-142, 1973. Burch CE, Shewey L : Sphygmomanometric
A. General Geddes LA: The Direct an and d Indirect Measurement of Blood Pressure. Year Book Medical Publishers, Inc., Chicago, 1970. JE : Pressure for Shulzecritical monitoring instruments care. SpaceLabs, Inc., Redmond, Washington, 1976. Washington,
and blood pressure cuff recordings. size JAMA 1973. 225:1215-1218, Steinfeld L, Alexander H, Cohen M: Updating sphygmomanometry. Am J Cardiol 33:107-110, 1974.
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gap p in sphygmoAskey JM : The auscultatory ga manometry. Ann Int Med 80:94-97 1974. Taguchi J T , Suwangool P: “Pipe-stem” brachial arteries: a cause of pseudohy pseudohypertension. pertension. JAMA 228:733, 1974. Maurer AH, Noodergraaf A A : Korotkoff sound filtering for automated three-phase measmeasurement of blood blood pressure. Am Heart J 91:584-591, 1976. Geddes U A , Whistler SJ : The error in indirect pressure measurement with the inblood pressure blood correct size of cuff. Am Heart J 96:4-8, 1978. Raftery EB : The methodology of blood pressure blood pressure recording. Br J Clin Pharm 6:193-201, 1978. Sacks AH: Sacks AH: Indirect blood pressure measurements: a matter of interpretation. interpretation. Angiology 30:683-695, 1979. Kirkendall WM, Kirkendall WM, Feinleib M Freis WD, Mark M,, Freis
AL: Recommendations pressure determination pressure by human determination for sphyg- blood momanometers. Stroke 12:555A-564A, 1981. Burke MJ Fitzgerald MJ,, Towers HM HM,, O’Malley K, K, Fitzgerald DJ, O’Brien ET : Sphygmomanometers in family practice: hospital and family practice: problems and recommendations. Br Med 285:468-471, 1982. Kristensen B O, and Kornerup HJ: Which arm to measure th the e blood pressure? Acta Med Scand (Suppl) 670:69-73, 1982. Prineas RJ , Jacobs D: Quality of of Korotkoff Korotkoff sounds: Bell vs diaphragm, cubital fossa cubital fossa v s brachial artery. Prey Med 12:715-7l9, 1983. Schrager BR , Ellestad M: The impor importance tance of blood pressure measurement during exerCardiovas Rev & Rep cise testing. Cardiovas Rev 4:381-394, 1983. Londe 5, Klitzner T S: Auscultatory blood pressure measurement: effect of pressure pressure on head of th the head the the e stethescope. Western Med 141:193-195, 1984. Med Gould B A, Hornung RS , Kieso HA, et al.: Is pressure the blood pressure blood the same in both arms? Clin Cardiol Cardiol 8:423-426, 8:423-426, 1985 . pressure measureConstant J : Accurate blood blood pressure ment. Postgrad Med 81:73-86, 1987. Yong PC, Geddes U A: The effect of cuff cuff pres-
Blank SC, West JE , Muller F Muller F B , et al.: Wideband external pulse recording during cuff deflation: a new technique for for evaluation evaluation of the arterial pressure pulse and meas meas-urement of blood pressure. Circulation 77:1297-1305, 1988. C. Inv Invasi asive ve Wood EH, Wood EH, Fuller I, Clagett OT : Intraluminal pressures recorded simultaneously from simultaneously from different arteries in man (abstract). Am J Physiol 167:838-839, 1951. Bevan A T, Honour A J, Stott FH: Direct arterial pressure recording in unrestricted man. Chin Sci Chin Sci 36:329-344, 1969. Stern DH, Gerson JI Gerson JI , Allen F B , Parker PB : Can we trust the direct radial artery pressure artery pressure immediately following cardiopulmonary bypass? (Abstract) Anesthesiology 57:A174, 1982. Abrams J : Arterial pulse and blood pressure. Cardiovas Rev & Rep 6:1055-1073, 1985. Cardiovas Gallagher JD , Moore RA, McNicholas K W , Jose radial and femoral arAB : Comparison of radial terial blood pressures in children after cardiopulmonary bypass. bypass. J C hi n Monit 1:168-171, 1985. Wesseling RI-I, Smith NT: Availability Availability of intra intraarterial pressure waveforms from catheter-manometer systems during surgery. J Clin Monit Monit 1:11-16, 1:11-16, 1985 . Bazaral MG, Nacht A, Petre J , et al.: Radial arsubclavian vian tery pressures compared with subcla pressure during coronary artery artery pressure artery surgery. Cleve C hi n J Med 55:4-48-457 1988.
D. Automated Moskowitz R : Spotlight on blood pressure blood pressure monitors—manual, automatic, and in be-
tween. Rx Home Care April, 1982. Moser M : Guide Guide to home blood pressure monitoring. Diagnosis 10(8):61-64, 1988. E . Miscellaneous Topics in Pressure Measurement Anliker M, Histand MB : Dispersion of small small artificial pressure waves in th the e canine aorta. Circulation Res Circulation Res 2 2 3:5393:539-551, 551, 1968. Nakayama R , Kobayashi T , Kimura K , Azuma T: A theoretical approach to the volume pulse wave. Am Heart J 86:96-106, 1973.
sure deflation rate on accuracy in indirect measurement of blood pressure blood pressure with the auscultatory method. J Clin Monit 31:155-159, 1987. Mariotti C, Alli C , Avanzani F , et al.: Arm positi tion on as a source a source of error in blood error pressure Clin Cardiol measurement. 10:591-593, 1987 Fedder DO , Frohlich ED , Zweifler A Zweifler A J: Sphygmomanometers: which to choose? Patient choose? Patient Care 21:67-70, April 30, 1987.
Newman DL Greenwald SE: Analysis of fo for r waves by a ward an and d backward pressure waves by total-occlusion method. Med Biol Eng Comput 18:241-245, 1980. Murgo JP Murgo JP , Giolma J Giolma J P, Altobelhi SA : Physiologic signal acquisition and processing for hu in a clinical man hemodynamic research hemodynamic research cardiac-catheterization laboratory. Proc IEEE 65:696-702, 1977.
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Association for th Association the e Advancement of Medical Medical Instrumentation: Standard for for electronic electronic or automated sphygrnoma automated sphygrnomanometers nometers (pro-
Henscheh A, de h a Vega F , Taylor HL: Simultaneous direct and indirect blood pressure measurements sure measurements in man at atre rest st an and d
the e Advancement posed). Associati Association on for th of Medical Medical Instrumentation, Arlington, Virginia, March, 1985. Ellis DM : Interpretation of beat-to-beat Ellis beat-to-beat blood pressure values in th the e presence of ye yen ntilatory changes. J Chin Monit 5-70, 1985. Ream AK: Mean blood pressure algorithms. J Chin Monit 1:138-144, 1985. Association for Association for the Advancement of of Medical Medical Instrumentation: Standard for electronic or automated sphygmomanometers. Association for th the e Advancement of Medical Medical Instrumentation, Arlington, Virginia, March, 1987. March, Smith NT: Computer Schwid HA, Taylor LA, Smith NT: model analysis of th the e radial artery pres artery pressure wavefo waveform. rm. J Clin Monit 3:220-228, 1987. Marmor Al Blondheim DS, Cozlan E, et al.: Method for noninvasive measurement of central aortic systolic pressure. Chin Cardiol 10:215-221, 1987.
ApphPhysiol 6:506-508, 1954. work. J ApphPhysiol 6:506-508, Berliner K, Fujiy H, Ho Lee D, et al.: Th e accuracy of blood pressure blood pressure determinations: a comparison of of direct and indirect meas meas-urements. Cardiologia 37:118-128,1960. Harrison EC, Roth CM, Hines EA: Bilate Bilateral ral indirect and direct arterial pressures. Circulation 23:419436, 1960 . lation Berliner K, Berliner K, Fujiy H, Ho Lee D , et al.: Blood pressure measurements pressure measurements in obese persons: comparison of intra-arterial and auscultatory measurements. Am J Cardiol 2 0 :10 -17, 1961. Coldstein 5, Killip T : Comparison of direct direct and indirect arterial pressures in aortic regurgitation. N EngI J Me d 267:11214124, 1962. Holland W W, Humerfeht Humerfeht S: S: Measurement of intrablood pressure: comparison of intraarterial and cuff values. values. Br Med J 2:1241-1243, 1964. Nagle FJ, Naughton J , Balke B : Comparisons of direct and indirect blood pressure-flow dynamics during exercise. Am J Physiol 21:317-320, 1966. JN: Bloo Blood d pressure measurement in Cohn JN: shock—mechanism of inaccuracy in auscultatory and palpatory methods. JAMA 199:972-976, 1967 London S B , London R London R E: Comparison of in indirect pressure measurements (Korotkoff) with simultaneous direct brachial artery distal to the cuff. Adv Int Med pressure distal to 13:127-142, 1967 Raftery E B , Ward A P: The indirect method of method of recording blood pressure. Cardiovas Cardiovas Res Res
III. COMPARISON STUDIES A. Indirect versus Direct Blood Pressure Measurement Warfield L M: Studies in auscult auscultatory atory blood pressure phenomena. Arch Tnt Med 10:258, 1912. Hamilton WF, Woodbury RA, Harper HT: Physiologic relationships between intrathoracic, intraspinal and arterial pressures. JAMA 107:853-856, 1936. Ragan C, Bordley J : Th e accuracy of clinical clinical arterial blood pressure, measurements of arterial with a note on the auscultatory gap. Bull Johns Hopkins Hosp 69:504-528, 1941. Steele JM : Comparison of simultaneous simultaneous indirect and d direct (intra-arterial) (auscultatory) an measurements of arterial arterial pressure in man. J Mount Sinai Hosp 8:1042-1050, 1941. Kotte JH, Ighauer A, McCuire J J:: Measurements of arterial blood pressure in th the e arm and blood pressure leg: comparison of sphygmomanometric sphygmomanometric and direct intra-arterial pressures, with special attention to their relationship in
2:210-218, 1968. Freis E D, Sappington F Sappington F : Dynamic reactions produced by deflating a blood pressure cuff. Circulation 38:1085-1096, 1968. of perYoungberg JA , Mifier E D: Evaluation of of the dorsalis cutaneous cannulations of Anesthesiology 44:80-83, pedis artery. Anesthesiology 44:80-83, 1976. Harrington D P : Disparities between direct and indirect arterial systolic blood-pressure measurements. CV P Aug/Sept:40-44, 1978. Hunyor SN, Hunyor SN, Flynn 3M , Cochineas C: Compari-
aortic regurgitation. regurgitation. Am Am Heart J 28:476-490, 1944. Roberts LN, Smiley JR . Manning CW: A comparison of direct and indirect blood pressure determinations. Circulation 8:232-242, 1953. A E, Van Bergen 5, Trehoar 5, Trehoar of FH, Dobkin A B,Weatherhead Buckley J J : Comparison indirect and direct methods of measuring arterial blood pressure. Circulation 10:481-490, 1954.
son of performance of various various sphygmomanometers momano meters with intra-arteriah blood-pressure readings. Br Med J 2:159-162, 1978. Bruner JMR, Krenis U, Kunsman 3 M , Sherman AP: Comparison of direct direct and indirect methods of measuring measuring arterial blood pressure, part T . Me Med d lnstr lnstr 15:11-21, 15:11-21, 1981.
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Bruner JMR, Krenis U, Kunsman JM, Sherman direct and indirect AP : Comparison of of direct methods of measuring measuring arterial blood pressure, part I I. Med Instr Instr 15:97-101, 1981. Bruner JMR, Krenis U, Kunsman JM, Sherman of direct direct and indirect AP : Comparison of measuring arterial blood methods of measuring pressure, part III. Med Instr 15:182-188, 1981. O’Callaghan WC, Fitzgerald DJ , O’Malley K, et al.: Accuracy Accuracy of indirect indirect blood pressure blood pressure the e elderly. Br Med measurements in th 286:1545-1546, 1983. Lersen B , Hoisten F , Poulsen HL: Nielsen PE, PE, Lersen Accuracy of ausculta pressure auscultatory tory blood blood pressure and d obese measurements in hypertensive an patients. Hypertension Hypertension 5:122-127, 1983. Nielsen FE : The The accuracy accuracy of auscuhtatory blood pressure measurement in the pressure elderly the elderly
Ceddes LA , Combs W, Denton W, et ah.: Indirect mean arterial pressure in the anesthetized dog. Am dog. Am J J Physiol 238 (Heart Circ Physiol 7): H664-H666, 1980. Mauck CW, CW , Smith CR, Ceddes LA, Bourhand JD: The meaning of the the point of maximum oscillations in cuff pressure pressure in the indirect measurement of blood pressure—part II pressure—part II . ASME J Biomech Eng 102:28-33, 1980 . Silas JH, Barker JH, Barker A T, Ramsey LE LE:: Clinical evaluation of Dinamap Dinamap 8 45 automated blood pressure recorder. Br Heart 1 43:202-205, 1980 . Friesen RH, Lichtor J JU: U: Indirect measurement of blood pressure blood pressure in neonates and infants utilizing an automatic noninvasive oscilhometric monitor Anesth Analg 60:742-745, Analg 60:742-745, 1981. Kimble K J, Darnall RA, Yehderman M, Ariagno RU , Ream AK: An automated oscillometautomated oscillomet
Acta Med Med Scand Scand fSuppj 676:39-44, 198R Vardan 5, Mookherjee 5, Warner R , Smulyan H: Syst Systolic olic hypertension: Direct and pressure measurements. indirect blood blood pressure measurements. Arch Int Med 143:935-938, 143:935-938, 1983. Rasmussen PH, Staats BA , Driscoll DJ, et al.: Direct and indirect blood pressure blood pressure during exercize. Chest 87:743-748, Chest 87:743-748, 1985. Hha 1 C M , Feussner JR : Screening for pseudohypertension: a quantative, noninvasive approach. Arch Int Med 148:673-676, 1988.
for estimating mean arterial nc technique pressure in critically il l newborns. Anesthesiology 54:423-425, 1981. Paulus DA : Noninvasive blood pressure meas meas-urement. Med Instr 15:91-94, 1981. Borow KM, Newburger esti Newburger 3 3 W : Noninvasiye estimation of central central aortic pressure pressure using using the th e oscillometric method for analyzing systemic artery pulsatile blood flow. Am Heart J 103:879-886, 1982. Ceddes LA , Voelz M, Combs C, Reiner D , Babbs CF: Characterization of the the oscillometric method for measuring indirect blood pressure. Ann Biomed Eng 10:271-280, 1982. Cohan SD , Fujii A, A, Borrow KM, Borrow KM, et al.: Noninvasive determination of systolic, diastolic and end-systolic blood pressure in neo and d young children: Co nates, infants an Com mparison with central aortic pressure measurements. Am J Cardiol 52:867-870, 1983. F: A Cloyna DF, Huber F , Abston F , Arens J JF: comparison of blood pressure measurement techniques in th the e hypotensive patient (abstract). Anesth Analg 63:222, 1984. Finnie KJC, Finnie KJC, Watts DC, Armstrong PW PW:: Biases in th of arterial arterial pressure. the e measurement of
B . Doppler Devices versus References Stegall H F, Kardon M B, Kemmerer WT: Indirect measurement of arterial blood pressure by Doppler ultrasonic sphygmomanome AppI Physiol try. J AppI Physiol 25:793-798, 1968. McLaughlin CW, CW, Kirby Kirby R R, Kemmerer W T , deLemos R A: Indirect measurement of pressure in infants utilizing Dopblood pressure blood Pediatr 79:300-303, 1971. pler ultrasound. J Pediatr 79:300-303, Sheppard L C, Johnson 33, Kirklin JW: Controlled study of brachial brachial artery blood pressure measured by a new indirect pressure method. J AAMI 5:297-301, 1971. CM, Remington Remington RD : Labarthe DR, Hawkins CM, Evaluation of selected selected devices for for measur measur-ing blood pressu pressure. re. Am Am J J Cardiol 32:546-553, 1973.
C. Oscillometric Devices Devices versus References Fosey JA , Ceddes LA , Williams H, Moore AC: maximum The meaning of the the point of maximum oscillations in cuff pressure in th the e indirect measurement of blood blood pressure Part I. Cardioyasc Res Cardioyasc Res Ctr Bull 8:15-25, 1 9 6 9 . Ramsey M: Noninvasive automatic determination of mean arterial pressure. Med Biol Eng Comput 17:11-18, 1979. Yelderman M, Ream A K: Indirect measurement of mean mean blood blood pressure in the anesthetized patient. Anesthesiology 50:253-256, 1979.
Cdt Care Care Me Med d 12:965-968, 1984. Davis R F: Clinical comparison of automated automated and d auscultatory and oscillometric an catheter-transducer measurements of arterial pressure. J C hi n Monit 1:114-119, 1985 . U , E Bennet R , Couture Nystrom Nystrom E E , Reid monds HU :KH, A comparison of two two auto auto- dmated indirect arterial blood pressure blood pressure meters: with with recordings from a radial arterial catheter in anesthetized surgical patients. Anesthesiology 62:526-530, 1985 .
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Venus B , Mathru M, Smith RA, Pham CG: Direct versus indirect blood pressure measurements in in critically critically ill patients. Heart & Lung 14:228-231, 1985. Loubser PC: PC: Comparison of intra-arterial intra-arterial and automated autom ated oscillomeft oscillomeftic ic blood pressure measurement methods in postoperative hypertensive patients. Med Instr 20:255-259, 1986. Cullen PM, Dye J , Hughes DC: Clinical Clinical assess assess-ment of th the e neonatal Dinamap 847 during and d infants. J din anesthesia in neonates an Monit 3:229-234, 1987 Shimazu H, Kobayashi H H,, Ito H, et aL: Indirect measurement of arterial pressure in the limbs of babies and children by th the e oscillometric method. J Gin Eng volume oscillometric volume 12:297-303, 1987. Whalen P , Ream A K: A quantitative evaluation of the Hewlett-Packard 78354A noninva of noninva- blood pressure meter. J Clin Monit sive 4 : 21 - 30 , 1 9 88 .
YamakoshiK, Rolfe YamakoshiK, Rolfe F , Murphy C: Current developments in non-invasive measurement of arterial arterial blood pressu pressure. re. J Biomed Eng 10:130-137, 1988. Santucci S , Steiner M, Zimbler M, et at: Validation study of th the e SpaceLabs models 90202 and 5200 ambulatory bloodpressure monitors. J Ambulatory Monk 1:211-216, 1988.
IV. FREQUENCY CHARACTERISTICS FO FOR R INVASIVE BLOOD PRESSURE MEASUREMENT Wood EH: Study of of minimal minimal dynamic response characteristics of manometer manometer systems required for adequate recording of peripheral arterial pressure pulses in man (abstract). Am J Physiol Physiol 163:762, 195 0 . Wood EH: EH: Physical response response requirements requirements of pressure transducers fo r the reproduction of physiological physiological phenomena. AWE AWE Trans Trans Part 1 : Communications & Electronics 75:32-40, 1956. Fry DL: Physiologic recording by by modem modem instruments strume nts with particular reference to pressure recording. Physiol Rev
Latimer KE , Latimer R D : Measurements of pressure-wave transmission in liquidfified tubes used for used for intravascular blood pressure recording. Med Biol Eng 7:143-168, 1969. Melbin J , Spohr M: Evaluation an and d correction of manometer manometer systems with two t wo degrees of freedom. freedom. J Appl Physiol 27:749-755, 1969.
HR, Toronto Toronto A Y , Gaisford Gardner RM, Warner HR, WD: Catheter flush syste system m for contirtuous monitoring of central arterial pulse waveform. J Appl Physiol 29:911-913, 1970 . McCutcheon H’ H’,, Evans ifi Stanifer NP NP:: Direct blood pressure measu measuremen rement: t: gadg gadgets ets
versus progress. Anesth Anaig 51:746-758, Anaig 51:746-758, 1972. LaPointe AC , Roberge FA : Mechanical damping of the manometric system used in the of pressure gradient technique. IEEE Trans
Biomed En g BME-21:76-78, Ackerman E, Leonard A: 1974. Klee C, Computer detection of distortion in arterial pressure signals. IEEE signals. IEEE Trans Trans Biomed Eng BME-21:73-75, 1974. Krovetz U, Coldbloom S : Frequency content of intravascular and intracardiac pressures and theft time derivatives. IEEE Trans BiEng BMIE-21:498-501, 1974. omed Eng LimiKrovetz U, Jennings RB , Goldbloom SD: Limitation of correction correction of frequency frequency dependent artefact in pressure recordings using harmonic analysis. Circulation 50:992-997, 1974. Hök B : Dynamic calibration of manometer manometer systems. Med Biol Eng 14:193 14:193-198, -198, 1976. Harf A, Lorino H, Atlan C, Laurent Proulx P A , Harf D: Dynamic characteristics of air-fified air-fified
differential pressure transducers. J Appi Physiol 46:608-614, 1979. Glantz B Glantz B A , Tyberg J V : Determination of frequency qu ency response from step response: application to fluid-fified fluid-fified catheters. Am J Physiol 2 Physiol Circ Physiol 5): 2 36 (Heart Circ Physiol H376-H378, 1 9 7 9 . Shinozaki T , Deane R S, Mazuzan JE: T he dy of liquid-filled catheter namic responses responses of systems for direct measurements o f blood blood pressure. Anesthesiology 53:498-504,
40:753 788, 1960. 788, 1960. JIM, Rosen AL, McDonald NM, Yanof JIM, of the the McDonald DA : A critical study of response of manometers to forced oscillaoscillations. Phys Me Med d Bioh 8:407-422, 1963. Vierhout R R, Vendrik JH: J H: On pressure generators for testing catheter manometer sys-
1980. Direct bhood bhood pressure measure measure-Gardner N NM: M: Direct ment: dynamic response requirements. Anesthesiology 54:227L 236, 1981.
V. INDICATIONS FOR/EFFICACY OF AMBULATORY BLOOD PRESSURE
tems. Phys Med Biol 10:403-406, 1965. Stegall HF: A simple, inexpensive, sinusoidal pressure generator. J Appi Physiol 22:591-592, 1967.
MONITORING Ayman D, Goldshine AD: Blood pressure determinations by patients with essential hypertension. Am J Med S d 200:465-474, 1940.
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Sokolow Sokolow M, M, Werdegar 1), Kain 1-1 K , Hinman A T: Relationship between level of blood blood
Mancia C, Bertiriieri C, Bertiriieri C, Grassi G, et al.: Effects of blood-pressure measurement by th blood-pressure measurement the e
and d by porta casually pressure pressure measured measured and severity severity of an complica complica ble recorders tions in essential hypertension. essential hypertension. Circulation 34:279-298, Circulation 34:279-298, 1966. J u l i u s S , E l l i s CN, P a s c u a l A M et al.: Home blood pressure determination. JAMA 229:663-666, 1974. L i t t l e r WA, Honour A J , Pugsley D J, Sleight DJ: Continuous recording o f direct arterial pressure itt unrestricted patients; its role in th the e diagnosis and management of high blood pressure. Circulation 51:11014106, 1975 . Gordon T Gordon T , Sorlie P , Kannel W B: Problems in the th e assessment of blood blood pressure: The Framingham study. T nt J Epidemiol 5:327-334, 1976. Millar-Craig MW Hawes D , Whittington J : New
and doctor on patient’s blood pressure blood pressure Lancet ii:695-698, heart rate. 1983. Devereux RB , Pickering TC, Harshfield GA, et at: t: Left Left ventricular hypertrophy in patients with wit h hypertension: hypertension: impor importance tance of blood pressure respons response e to regularly recurring stress. Circulation 68:470-476, 1983. Des Combes B J, Porchet MD, Waeber B , BrunBrunner H R: Ambulatory blood pressure recordings: reproducibility and unpredictability. Hypertension 6 Hypertension 6 :C 11O -C 115, 1984. Gould BA, Hornung RS , Kieso HA, et al.: Evaluation of the Remler Remler M2000 M2000 blood pressure recorder: comparison with intraintraarterial blood pressure blood pressure recordings recordings both at and nd at home. Hypertension hospital a 6:209-215, 1984. Sleight P: Sleight P: Ambulatory blood pressure monitor-
system for recording ambulatory blood pressure in man. Med Biol Eng Comput 16:727-731, 1978. Perloff D, Sokolow D, Sokolow M: The representative blood office, basal, pressure: usefulness of office, home, and ambulatory readings. Cardiovasc Med Med 655-668; June, 1978. Floras JS, Floras JS, Jones Jones Jlv Hassan MO, et at: Cuff and ambulatory blood pressure in subjects with essential hypertension. Lancet 11: 10 7- 10 9 , 1981. Sheps SC, Elveback L R, Close E EL, L, et at: Evaluation of ation of th the e Del Mar Avionics automatic ambulatory blood pressure-recording device. Mayo Curt Mayo Curt Proc 56:740-743, 1981. Fitzgerald D J, O’Callaghan WG, McQuaid R , et al.: Accuracy and reliability reliability of two two indirect ambu pressure record record-ambulatoryblood latoryblood pressure ers: Reniler M2000 Reniler M2000 and Cardiodyne Sphygmolog. Br Heart J 48:572-579, 1982. Home readings of Andersen AR, Nielsen P PE: E: Home readings pressure in evaluation of of hyperten blood pressure blood hyperten-sive subjects using a new self reco recordi rding ng manometer Ada Med Scand (suppi) 670:97-104, 1982. Weber MA, Drayer JIM, Wyle FA , Brewer DD: A representative value for whole-day BP monitoring. JAMA 248:1626-1628, 1982.
ing. Hypertension 7:163-164, Hypertension 7:163-164, 1985. Parati C, Parati C, Pomidossi G, Casadei R Casadei R , Mancia C: alerting reactions to intermittent Lack of alerting reactions cuff inflations inflations during noninvasive blood pressure monitoring. Hypertension 7:597-601, 1985 . Creevy PC, Burns J JF, F, Mroczek WJ: Phlebitis associated sociate d with noni noninvasive nvasive 24-hou 24-hourr ambulatory bulato ry blood pressure monitot JAMA 254:2411, 1985 . Hunt JC, Frohuich E D, Moser M, et al.: Devices used for self-measurement of blood blood pres Revised statement of th sure: Revised sure: the e National High Blood High Blood Pressure Education Education Program. Program. Arch m t Med 145:2231-2234, 1985. White WB : The Rumpel-Leede sign associated with a nonirivasive ambulatory blood pressure monitor. JAMA 253:1724, 1985. Drayer JIM, JIM, Weber Weber MA, Hoeger WJ : Whole-day BP monitoring in ambulatory normotertsive men. Arch T n t Med 145:271-274, 1985. Weber MA, Drayer JTM, Brewer DD: Brewer DD: Automated MA, Drayer blood pressure measurements in th the e diagnosis of mild agnosis Cardi- mild hypertension. J Cardi opuim Rehabil 6:125-130, 6:125-130, 1986. Frohlich ED: Frohlich ED: Ambulatory blood pressure moni blood pressure toring: what is known and not known in 1 9 8 6 . Learning Center Highlights, Highlights, Ameri Ameri--
Perloff D , Sokolow M, Sokolow M, Cowan R: The prognos prognos-tic value of ambulatory ambulatory blood pressures. JAMA 249:2792-2798, 1983. Drayer JIM, Weber MA, DeYoung JL, Brewer JIM, Weber Long-term BP monitoring in th DD: Long-term DD: the e evaluation of antihypertensive therapy evaluation Arch m t Med 143:898-901, 1983.
cal College of Cardiology Cardiology 1:14, 1986. Health an and d Public Policy Committee, American College of College of Physicians: Automated ambu ambu-latory lato ry bloo blood d pressure monitoring. Ann m t Med 104:275-278, 1986. National Health Services and Practice Patterns Survey Report on Fully Automated Am-
Rowlands D B, Stallard ‘fl, Littler WA Littler WA : Comparison of ambulatory ambulatory blood pressure and cardiovascular reflexes cardiovascular hyper- reflexes in elderly hyper tensives, elderly norntotensives an and d young hypertensives. J Hypertension 1 (suppi 2)11-73, 1983.
Blood Monitoring: Cur Monitoring: bulatory Applications rent and Future Pressure National Academy of Academy of Sciences, Sciences, Washington, DC; March 5 , 1986. Baker LH: Episodic hypertension White WB , Baker LH: secondary to panic disordet Arch Tn t Med 146:1129-1130, 1986.
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Spacelabs Medical: BLOOD PRESSURE
\, \ ,
automatic blood presKay J , Neal M: Effect of automatic sure devices on vigilance of anesthesia J residents. Clin Monit TG, Harshfield GA, 2:148-150, Blank S, et al.: Pickering S , 1986. Behavioral determinants of 24-hour 24-hour blood pressure patterns pressure patterns in borderline hypertension. J Cardiovas Pharm 8 (suppl 5):S89-S92, 1986. Pickering TG: Strategies for th the e evaluation and treatment of hypertension and some implications of blood pressure blood pressure variability. Circulation 76(suppl I ):177-182, 1987. Pagny JY~ Pagny JY~Chatellier Chatellier C, C, Devries C , et al.: Evaluation of the the SpaceLabs ambu’atory blood pressure recorder: comparison with the M2000. Cardiovas Rev & Rep Remler M2000. Remler April 1987. Krakoff L L R, Phfflips RA : Ambulatory blood pressure monitoring in management of hypertension. Primary Cardiol 16-26, April, 1987. Celoria C, Dawson JA Celoria JA,, Teres D: Compartment syndrome in a patient monitored with an automated blood pressure blood pressure cuff. J Clin Monit 3:139-141, 1987. Mancia C, Parati G, Parati G, Poniidossi G, et al.: Alert Alert-ing reaction and rise in blood pressure during measurement by physician an and d nurse. Hypertensio Hypertension n 9:209-215, 1 9 8 7 . Baker LH: Ambulatory blood presWhite W B, Baker LH: sure monitoring in patients with panic disorder. Arch T nt Med 147:1973-1975, 1987. Fortmann SP , Haskell WL , Wood PD , et al.: Ef fects of weight loss on clinic and ambulatory blood pressure in normotensive blood pressure men. Am J Cardiol 62:89-93, 1 9 8 8 . Pickering TG, James G D, Boddie C, Boddie C, et aL: How
Caliva FS, Napodano R RJ, J, Lyons RI-I: Digital hemodynamics in th the e normoterisive an and d
hite e coat is whit hypertension hyperte nsion? ? common JAMA 259:225-228, 1988. Weber MA, Weber MA, Cheung DC, Graettinger WF, Lipson JL: Characterization of antihyper antihypertensive therapy by whole-day blood pressure monitoring. J Am Med Assoc 259:3281-3285, 1988. White WB , Morganroth J : Usefulness of ambulatory monitoring of blood pressure blood pressure in assessing antihperten antihpertensive sive therapy. (Editorial) Am 3 Cardiol 63:94-98, 1989.
and d simultaneously measured methods an direct intra-arterial pressure. Br J Anaesth 57:434, 1985. Wesseling KH, Wesseling KH, Settels J J , De Wit B : The measurement of continuous continuous finger fin ger arterial pressure noninvasively in stationary su sub b jects. In Biological and Psychological Factors in in Cardiovascular Disease. Schmidt TI-I, Dembroski TM, and Blumchen C, (Eds.), Springer-Verlag (Eds.), Springer-Verlag,, Berlin, 1986,
states. II . 1963. Venomotor tone. hypertensive Circulation 28:421-426,
B . Continuous Measurement Measurement YamakoshiK, Shimazu H, Shimazu H, Togawa T : Indirect measurement of instantaneous arterial pressure in th the e rat. Am J Physiol blood pressure blood 237:H632-H637, 1979. YamakoshiK, Yamakoshi K, Kamiya A, Shimazu H, et al.: al.: of i inNoninvasive automatic monitoring of stantaneous arterial blood pressure using the vascular unloading technique. Med Biol Eng Comput 21:557-565, 1983. Wesseling KH, Settels JJM, Settels JJM, et al.: Moihoek CF. CF. Wesseling KH, Evaluation of the the Penaz servo-plethysmothe e continuous, manometer for th continuous, non finger blood invasive measurement of finger pressure. Basic Res Cardiol 79:598, 1984. Dorlas JC, Nijboer JA JA,, Butija W Butija W T, et al.: Effects of peripheral peripheral vasoconstriction on th the e blood pressure in the finger, measured continuously by a new noninvasive method (the Finapres). Anesthesiology 62:342-345, 1985 . Gravenstein JS, Paulus DA , Feldman J , and Mc[.aughlin C: Tissue hypoxia distal to a Penaz finger blood pressure blood pressure cuff. J din Monit 1:120-125, 1985. Smith NT, Wesseling KR, de Wit B : Evaluation of two two prototype devices producing noninvasive, palsatile, calibrated blood pressure measurement pressure measurement from from a finger. J Cliri Monit Monit 1:17-29, 1:17-29, 1985. Van Egmond J , Hasenbos M, Cml J F: Invasive vs noninvasive measurement of arterial arterial pressure Comparison of tw two o automatic
VI.. VI
pp. 355 375. real-time, noninva noninva-Boehmer RD : Continuous, real-time, sive monitor of blood blood pressure: Penaz methodology methodo logy applied to th the e finger. J Gun Monit 3:282-287, 1987. Kurki T , Smith N T, Head N, et al.: Noninvasive continuous blood pressure blood pressure measurement from the finger: optimal measurement and d factors affecting reliability. conditions an J Clin Monit 3:6-13, 1987.
FING FI NGER ER BLOOD PRESSURE A. Digital Hemodynamics Mendlowitz M, Torosdag SM, Sharney L : Force and work of of digital arteriolar smooth muscle contraction fr frii hypertension. J Appi Physiol 10:436-446, 1957. Caliva FS, Napodano R RJ, J, Stafford RM, J~oftus W, Lyons RH: Digital hemodynamics in the normotensive an and d hypertensive states. I. Digita’ mean arterial an and d venous pressures, blood flow, and vascular resistance. Circulation 28:415-420, 1963.
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H, Kobayashi H, Ito Ito H, Yamakoshi K: Shimazu Shimazu H, Indirect measurement of arterial pressure in th the e limbs of babies the e babies and children by th volume oscifiometric method. J Cliii Monit 12:297-303, 1987. C. Inter Intermitten mittentt Measurement Lassen NA NA,, Krahenb.hl B , Hirai M: Hirai M: Occlusion cuff for routin routine e measu measuremen rementt of digital blood pressure and blood flow. Am J Physiol 232:H338-H340, 1977 Yamakoshi K, Kawarada A, Kawarada A, Kamiya A, Kamiya A, et al.: Long-term ambulatory monitoring of indirect arterial blood pressure using a direct volume-oscifiometric method. Med Biol Eng Comput 23:459-465, 1985. Shimaz Shi mazu u H, Ito H, Yamakoshi K: Noninvasive method for estimating th the e mean capillary pressure and pre- an and d postcapfflary resistance ratio resistance ratio in human fingers. Med Biol Eng Comput 24:585-590, 1986.
VII. NONINVASIVE MEASUREMENT OF ARTERIAL COMPLIANCE Nakayama R , Azuma Azuma T T : Noninvasive measurements of digital arterial pressure and compliance in man. Am J Physiol 233:H168-H179, 1977. 233:H168-H179, 1977. Yamakoshi K, Shimazu H, Shimazu H, Togawa T , Ito H: Admittance plethysmography for accurate measurement of human human limb blood flow. Am J Physiol 235:H821-H829, 1978. Simon AC, Safar ME, Levenson JA , et al.: An evaluation of large arteries compliance in man. Am J Physiol 237:H550-H554, 1979. ZhangShang-da C, Xue-han N, Chao-nien Chao-nien C C , Zhangming C: Noninvasive determination of arterial compliance. Med Biol Eng Comput 21:424-429, 1983. Bell L B , Zuperku EJ , Kampine JF: Technique for Technique for measurement of compliance compliance continuous measurement continuous in isolated vascular Physvascular segments. segments. Am I Physiol 250:R142-R149, 1986.
8 . 0 GL O SSA R Y Action potential The The electrical activity developed in a muscle or nerve cell during activity. Algorithm — A procedure for solving a mathematical problem in a finite number of steps steps that frequently involves repetition of an operation. Moving or extending extending forward; Antegrade Moving forward; also called anterograde. Aorta T he great trunk artery that carries blood from the he hear artt for distribution by th the e branch arteries throughout th the e body. —
—
—
Of or or pertaining to the aorta. Aortic — Of Arrhythmia An alteration of either either time or force of the th e rhythm of the the heartbeat. One of the Arteriole One the small endings of an an artery that becomes the capillaries. Arteriosclerosis A group of diseases diseases characteriz characterized ed by thickening and loss of elasticity of elasticity of arter arterial ial wall walls. s. Artery — A vessel or tube-like structure through which the blood passes away from the from the heart to the various the various parts of of the body. —
—
—
Atrium — A chamber; used in anatomical nomenclature to designate a chamber allowing or organ; organ; usually entrance to another structure structure or usually used alone to designate a chamber of the the heart. chamber(s) (s) of the he Auricle — The chamber heart art that receives blood from the veins and forces it into the ventricle(s). Used most commonly in reference to nonhuman anatomy. Auscultate — T o examine by listening, usually to to the the sounds of sounds of the the thoracic or abdominal visce viscera ra with or without a stethoscope. Auscultation The act of listening f or sounds within the body, chiefly for ascertaining the condition of the the heart o r other organs. Of or or pertaining pertaining to auscultation; a Auscultatory — Of noninvasive method of blood pressure measurement. A-V valves — See atrioventricular valves. Having tw Bisferious two o beats; usually refers to a widely notched arterial pulse that is sometimes —
—
Artifact Any structure or feature that is not normal or natural; distortio distortions, ns, abberati abberations, ons, and inaccuracies of the the normal blood pressure waveform. Atria Plural Plural for atrium (See definition below). Atrial kick — Same as atrial systole (See definition —
—
below). systole Phase of of the cycle that Atrialcorresponds to the atrialatrial contraction. Atrioventricular valves Valves located between the cavities of the the atrium and ventricle in each half of the heart; these valves permit blood to flow of from the atrium to to the the ventricle bu butt not from the ventricle to the to the atrium.
palpable. Bronchial or more bronchi. Pertaining to one one or Bronchus (p1. bronchi) Any of the the larger air an outer passages of th the e lungs, having an outer fibrous coat with irreg irregularly ularly placed plates of hyalin hyalinee cartilage, an interlacing of smooth smooth muscle, and a mucous membrane of columnar columnar epithelial cells. —
—
—
—
—
Capacitance Any See compliance. Capillaries of th the e smallest vessels of the the system vascular that connects an arteriole with a venule to complete the formation of blood vessel networks throughout the body. Pertaining to the heart. Cardiac —
—
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Spacelabs Medical: BLOOD PRESSURE
Cardiac cycle — The period from the end of one one the e end of the next heart contraction t too th
the e size of French scale — A scale used for denoting th catheters, sounds, and other tubular tubular instruments instruments
the th e cardiac cardiac cycle cycle of a b contraction; consists relaxation n called period of of relaxatio diastole followed byy a period of of contra contraction ction called called systole. systole. Cardiac output — The volume of blood blood pumped by each ventriche per minute; minute; cardiac output is expressed as liters per per minute. Cardiac usually expressed usually output is determined by multiplying the he heart art rate and th ejected by each the e volume of blood blood ejected ventricle during each heart beat (stroke volume) stroke volume}. [Cardiac output = heart rate X stroke volume}. Catheter — A tubular medical medical device device for for inserting into canals, vessels, passageways, or body c a v i t i e s t o permit injection injection or withdrawal of fluids, to keep passages open, or to measure an fluids, body parameter. internal body Catheter whip — Oscillation of the the tip of the the catheter in time with th the e cardiac cycle during the movements of th the e heart. Catheter whip
to 0.33 with ineach unit being roughly rou ghly equivalent (for example, mm diameter an 18 French measurement is is equivalent equivalent to adiameter of 6 mm). period-Frequency — The number of occurrences of a period time; ic process in a unit of of the th e number of vibrations made by a particle or ray in one second; in electricity, the rate of oscillation oscillation or alternation in an alternating current. Frequency response — The upper and lower lower frequen frequen-cies at which the which the amplitude response ha has s fallen to 3 decibles below the mid-frequency value. Heart failure — A clinical syndrome characteriz characterized ed by distinctive symptoms and signs resulting from disturbances in cardiac output or from increased venou venouss pressure. Most often applied to myocardial failure myocardial failure with increased pressures di dis stending th the e ventricle (high end-diastolic pressure [EDP]) of of the heart and a cardiac output
produces artifacts that are are superimposed superimposed upon upon pressure pulses recorded during invasive the pressure the recorded during b l o o d pressure measurement. pressure measurement. venous pressure (CVP) — The venous Central pressure as measured at the right atrium; also called right atrial pressure (RAP). Compliance — A quality of yielding yielding to pressure or force w without ithout disruption, or an expression of the th e measure of the the ability to do so, as an expression of the distensibility of an air- or fluid-filled organ, eg., the lung or urinary bladder, in terms of unit of volume volume change per u n i t o f pressure change. Damping — The process of decreasing the amplitude of a wave; th the e ‘shock absorber’ absorber’ effect of retarding free vibrations in the catheter monitoring system. Diastasis — The middle middle third of diastole when the blood into the ventricles has nearly inflow of inflow of blood stopped; the rest period of the the cardiac cycle that occurs just just before systole. dilatation of Diastole — The dilatation or period of dilatation especially of the ventricles; diastole the th e heart, especially of coincides with the interval between th the e second and first heart sounds. Diastolic — Of or pertaining to diastole. Dicrotic — Having a double beat; double beat; related related t too the
inadequate for the body’s needs; often subclassified as sified as right- or left-sided heart failure depending on whether th the e systemic or pulmonary veins are predo predominantly minantly distende distended. d. Hemodynamics — The study of movements movements of the the and d of the the forces associated with the blood an blood system. Hertz — A unit of frequency equal to one cycle per second; abbreviated Hz. Hydrostatic — Pertaining to a liquid in liquid in a state of equilibrium. pressure — The pressure at any level on Hydrostatic pressure Hydrostatic due e to th weight of the water (or blood) at rest du the e weight the above it. water (or blood) above it. Hypertension — Persistantly high arterial blood pressure. Hypertrophic — Pertaining to or mark marked ed by hypertrophy Hypertrophy — The enlargement or overgrowth of an an organ or part due to an increase in size of its constituent cells. Hypotension — Abnormally low blood pressure; seen in patients with shock but not necessarily indicative of this condition. Incisura — A cut, notch, or or incision; incision; th the e notch in the aortic and pulmonary arteryblood pressure arteryblood pressure waveforms which occurs when th the e semilunar valves close. valves close. The incisura is caused by a short
sound expansion of the dur r the artery that occurs du ing th the e diastole of th the e heart. Dilation — The action action of of dilating dilating or stretching. Dilatation — The condition of being being dilated or beyond the stretched beyond stretched the normal dimensions; the stretching an orifice or tubular act of dilating dilating or or stretching structure, for for example. example. Distal — Remote; farther from any reference; from any point of reference; opposed to proximal.
End-diastolic volume — The amount of blood blood in the
ventricle just prior to systole. Endothelium — The layer of epithelial cells that lines cavities of the th e cavities of the the heart, the serous cavities the th e body, and th the e vessels vessels of the the blood and lymph systems.
period of backward backward flow of blood blood immediately prior to closure of th the e valves. Interstitial — Pertaining to or situated between parts or in th the e interspaces of a tissue. Intrapleural space — The space within the pleura definition efinition below below). ). (See d Isometric — Maintaining, or pertaining to, the same measure of length; length; of equal dimensions; not isotonic. contraction — The first phase of venIsovolumetric tricular systole; begins with th the e closure of th the e atrioventricular valve and ends with the opening of the the semilunar valve. Tension increases in the muscle bu butt no shortening of the muscle
fiber occurs.
105
Isovolumetric relaxation — T phase of ventric ventric The he first phase
Resistance — Opposition or counter-acting force; an
the ular diastole; begins with the closure of the semilunar valve (See definition below) an and d ends with the with the opening of th the e atrioventricular valve. Mean pressure — The average of all all values values of pressure observed at th the e measurement site over a number of cardiac cycles. Mitral valve — A cardiac valve that consists of two triangular flaps and guards the orifice between ventricle; icle; also called th the left atrium and ventr the e bicuspid valve. Myocardium — The middle and thick thickest est layer of the the cardiac muscle. heart wall; composed of cardiac Natural frequency — T he frequency at which an ob ject or or system system wifi wifi vibrate if struck and and allowed to vibrate freely. Oscillation — A backward an and d forward motion, like a fluctupendulum; also described also described as avibration, fluctuation, or variation. Oscillometer — An instrument for measuring oscilla measuring oscillations of any any kind, such as changes in th the e volume of th the e arteries accompanying th the e heart beat. Palpation — T he act of feeling with the hand; the the hand; the apfingers w plication of th the e fingers with ith light pressure to the surface of the the body to determine the co consis nsistence of parts parts beneath th the e surface in a physical examination. Percutaneous — Through the skin. Pericardial — Pertaining to th the e pericardium (See (See definition below). the e Pericardium — The fibroserous sac that surround th roots of of the great vessels, vessels, comheart and the roots prised of an extemal layer of fibrous fibrous tissue an and d an inner serous layer. The base of th the e pen-
impediment to blood flow in a vessel. Going backward; retracing a former Retrograde — Going course. S-A node — See definition belowfor sinoatrial node. Semilunar valve — A A valve valve having semilunar (resembling a crescent or half-moon) cusps; for example, th the e aortic valve and the pulmonic valve. Septum — A dividing wall or partition. Sinoatrial node — A microscopic collection of collection of atypical atypical cardiac muscle fibers at the superior end of the the sulcus terminalis and at the at the junction junction of of the superior vena cava and tight atrium; also called sinus node. The cardiac rhythm normally b be egins at the sinoatrial node so that this node is of the heart. also known as the pacemaker of Snap test — The quick test used in a clinical situation to assess the amount of damping damping of a pressure measurement system, which provides a reasonable reasonab le estimati estimation on of th the e step response of this system. Stroke volume — The amount of blood blood ejected from a ventricle at each beat of the the heart. Swan-Gan.z catherter — A type of lklley lklley catheter with an inflatable inflatable balloon located close to th the e tip; th the e balloon expidi expidites tes passage of the the catheter blood) through th the e he hear artt (following the flow of blood) and obtains the wedge pressure reading. Systole — The contraction, or period of contraction, of the heart, especially that of th the e ventricles. Systole coincides with the interval between the first and second heart sound during which blood is forced into the aorta and the pulmonary trunk. Systolic — Pertaining to or produced by th the e systole; occuring along with the ventricular systole.
is attached to th the e central tendon of the the cardium diaphragm. Peripheral resistance — The resistance to th the e passage espeof blood through the small blood ve vessels, ssels, especially the arterioles. Peripheral resistance unit (PRU) — The unit used to measure measur e resistance in a blood vessel, usua usually lly given in milli millilite liters rs (ml) of mercury mercury per mffliiter (ml) per per minute. minute. Phlebostatic axis — The reference point point for human for human
— Relatively rapid heart action. Tachycardia the e chest. Thoracic — Pertaining to or affecting th converts ts fluid pressures Transducer — A device that conver to electrical voltages. Standardized transducers interchangeable eable because they generate th are interchang the e voltage output per unit of fluid same amount of voltage pressure applied. The resting output voltage of the th e transducer is known as the offset with th the e pressure applied the e sensing atmospheric pressure atmospheric applied to th membrane, which if often often some other value
blood pressure measurement; blood pressure measurement; located at th the e level of the the atria. Pleura — The serous membrane investing an and d inter inter- and d lining lining of of th spersed throughout th the e lungs an the e thoracic cavity, completely enclosi enclosing ng a potential space known as the pleural cavity. T wo distinct pleurae exist, tight an and d left, both of which are moistened with a serous secretion that facili the e movements of the the lungs in th the e chest tates th cavity. Protodiastole — Early diastole; th the e period of slow during th ejection during ejection the e ventricular cycle. Proximal — Nearest; closer to any point of reference; opposed to to distal. distal. Pulse pressure — T The he difference between the systolic and diastolic pressures.
than 0 volts. Tricuspid valve — The valve composed of three three flaps reflux of the e reflux of blood blood from the right that prevents th ventricle to th the e tight atrium. caliber of Vasoconstriction — The lowering of th the e caliber of con nblood vessels, especially the tightening or co striction of the the arterioles leading to decreased blood flow to that body part. Vasodilation — Dilation or opening up opening up of a blood vessel, vesse l, especi especially ally of of th the e arterioles leading to increased blood flow to that body part. Ventricle — A chamber of the the heart that receives from a corresponding atrium and from blood from which blood which forced into th blood i iss forced into the e arteries.
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Spacelabs Medical: BLOOD PRESSURE
N’
Venae cava — The vena cava inferior an and d superior
Venule — A small vein; small vein; especially on one e of the the minute
below). (See inferior definitions Vena cava Vena cava — The inferior vena cava; th the e venous trunk for th and d for the e lower extremities an the pelvic an and d abdominal viscera; it begins at the th e level of the the fifth lumbar vertebra where the common iliac veins unite, passes upward on the th e right of th the e aorta, and empties into th the e tight atrium of th the e heart. Vena cava superior — The superior vena cava; th the e venous trunk draini draining ng blood from the head, neck, upper extremeties, and chest; it begins where th the e two brachiocephalic veins unite, passes directly downward, and empties into th the e rightt atrium of the heart. righ
the capifiary bed with the veins veins. larger connecting systemic veins. systemic Volumetric compliance — The amount of volume volume increase per unit of applied applied pressure in th the e catheter pickup system; usually due to to elasticity elasticity of components. components. Wedge pressure — Intravascular pressure as measmeasured by a catheter introdu introduced ced into th the e pulmo pulmo- pressure provides nary artery; the wedge pressure provides an indirect measurement of the mean left atrial pressure. sys sZeroing — Adjusting th the e pressure measurement sy tem for a reading of “0” “0 ” while applying atmospheric pressure to th the e sensing membr membrane; ane; some amplifiers have automatic, push-button type zeroing.
INDEX Aortic pressure measured by Aortic semilunar valve Arterial pressure mean peripheral, catheters Arterial system Arteries Arterioles Arteriosclerosis Atrial cycle Atrial kick (systole) Atrioventricular (A-V) ‘nodes
52 52
valves measurement Auscultatory gap Korotkoff sounds limitations sources of error sphygmomanometer Automated noninvasive measurement auscultatory auscu ltatory method
S
31 41, 43 3, 7 3 9 37 17 15, 17
11 S
76, 78, 86 79 78 81 81 76 86 86
invasive measurement method methodss 41-77 (same as (same as direct methods) mean, transmiss transmission ion 31 measurement by fluidf i f i e d systems 53, 57, 59, 61 noninvasive measurement methods 76-93 (same as i n d i r e c t methods)
respiratory effects on measurement 76 transducers 53, 57, 59, 61, 64, 66, 69 zeroing transducers 76 Capacitance Capillaries Cardiac cycle
9 9 11, 17
(a, v) 17 v) waves pressure Cardiac output c, 5 Catheter(s) central pressure 43, 48 constant infusion system 61 diameter (scales) 43, 44 French scale for 43, 44 impact, pressure measurement artifact .. . . 70, 73 insertion 41
Doppler method oscillometric method
Blood pressure measurement auscultatory measurement auscultatory catheter impact (artifacts) catheter whip (artifacts) cuff size, recommended damping direct measurement methods (same as invasive methods) end pressure (artifacts) errors in measurement indirect measurement metho methods ds (same as noninvasive methods) auscultatory
intravenous, dimensions left heart percutaneous pulmonary artery pulmonary M right heart (Swan Gan z’ ) Stubbs gauge scale for surgical cut-down Swan Ganz” (right heart) transducers, catheter-tip whip, pressure measurement artifact Cardiovascular pressure adult normal values Catheter-tip transducer Central venous pressure (CVP) measured by
87 86, 93
76, 78, 86 70 70 81 38 41-77
70 , 73 70, 73 76-93
44 43 41 41, 48 41 43 41 41 41 70, 7 3
51 41, 66 48, 51 48
76, 78, 86
10 7
(cardiovascular) system Circulatory (cardiovascular) anatomy physiology Compliance C o n s t a n t i n f u s i o n system
3 3 3 7 64
Damping (of blood pressure measurement) 38 blood pressure measurement) frequency dispersion 38 frequency response 53, 57, 59, 61 of high frequencies 38 pressure wave reflection 39 ratio 53, 57, 59, 61 tapered tube effect 38 Diastasis 15 Diastole 15 Diastolic pressure transmission (A (AC C analogy) 37, 51 Dicrotic notch see Incisura see Incisura ultrasound Doppler ultrasound Doppler 87, 89 b l o o d pressure measurement pressure measurement
Doppler shift
End pressure pressure pressu re measurement artifact
89 87 70 , 73 70 , 73
F a s t F o u r i e r T r a n s f o r m (FF1)
analysis 21 Finger blood pressure measurement blood pressure measurement 91 continuous, noninvasive 91 91 photoplethysmograph Fluid-filled systems 53 measurement of blood pressure 53 Fourier series 21 French scale (catheter diameter) 43, 44 Frequency dispersion 38 Frequency response 53, 57, 59, 61 air bubbles an and d damping 61 fluid-filled system forced forc ed oscill oscillation ation method free oscillation method intravascular (catheter-tip) transducer optimization in clinic overdamping underdamping
Harmonic Harmo nic analysis
53 53 53, 57 66 59 53, 61 57 21
Korotkoff sounds five phases
78, 79 (table), 84 78, 79 (table)
Laminar flow Left ventricular pressure measured by
Mean systolic pressure definition equation Millar Mikro Mikro-tip’ tip’~ ~tran transducer sducer
Natural frequency of frequency frequency response Newtonian fluids NonNewtonian fluids Ohm’s Law Ohm’s Law Oscillation forced free
19 19 19 66 53 53, 57, 59, 61 27 27
23,27, 29
53 53
Peripheral arterial pressure catheters
25 51, 52 52
in children Peripheral Periph eral resistance resistance unit (PRU) Photoplethysmograph Phlebostatic axis Phlebostatic Poiseuille’s Law Precapillary sphincters Pressure transducer(s) Pressure transmission wave reflection Pressure wave reflection waves Pressure a wave c wave v wave
43, 44, 48, 51 41
43, 44 35, 36, 39 91 76 27, 29 33 41 19, 21 38 17 17 17 17
13 Protodiastole Pulmonary artery pressure artery pressure 36, 48, 51, 52 catheter for 48 mean 36, 51 measured by 52 wedge pressure (PCWP) . .36, 51 Pulmonary capillary capillary wedge measured by 52 3, 9 Pulmonary circulation mean 35, 51
blood pressure waveforms Heart anatomy functions Hydraulics Hydrostatic pressure vascular system Impedance vascular
29, 31
3 8 , 39
Incisura
Intravascular transducer catheter-tip
21 3 3 3 23 11 11
66 66
I s o vo l u m i c c o n t r a c t i o n
13
Pulmonary semilunar valve Pulmonary Pulmonary vascular resistance (PVR) equation Resistance, vascular Reynolds’ Number (Re) Right ventricular pressure (RVP) measured by
5 39 39
33, 35 25
51, 52
Servo control system finger blood pressure measurement Sinoatrial node Sphincter(s) precapillary
91 91 11 33
1 08
Spacelabs Medical: BLOOD PRESSURE
\~
Sphygmomanometer aneroid
76 78
size, recommended cuff size, mercury Strain gauge transducer Stubbs gauge scale for catheter diameter catheter diameter Systemic circulatio circulation n Systemic vascular resistance (SVR) Systole Systolic pressure amplification, peripheral definition pressure equation mean pressure mean equation transmission (A (AC C analogy)
81 76 64 64, 66
Tapered tube effect Transducer(s) catheter-tip disposable distortions in measurement errors in measurement Millar Mikro-tip’~ pressure respiratory effects strain-gauge type zeroing
43 3, 7, 9 36, 39 5 19, 51 38 19 19 37 38
41, 66 70 70 70 66 41 73 64 73, 76
Vascular impedance calculation of calculation
measurement Vascul Vas cular ar resistan resistance ce measures of peripheral resistance unit (PRU) systemic vascular resistance (SVR) equation Wood unit vascular resistance unit (\TRU) Veins Venous system Venous system Ventricular cycle isovolumic contraction protodiastole rapid ejection
Wood unit
29 29
31 34, 35 39 39 36 36 35, 39 35, 39 3,9 9 13 13 13 13
35, 39
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