criteria in the choice of an occluding cuff for the indirect measurement of blood pressure

Med. & Biol. Eng. & Comput., 1977, 15, 2-10

Criteria in the choice of an occluding cull' for the indirect measurement of blood pressure

Harold A lexander M y r o n L. Cohen

Stevens Institute of Technology, Hoboken, NJ 07030, USA

Leonard Ste infe ld The Mount Sinai School of Medicine, New York, NY 10029, USA

A b s t r a c t - - F o r a sphygmomanometr ic method of indirect blood-pressure measurement to be accurate, the cuff must operate sa that the intrabladder pressure is always the same as the pressure appl ied by the tissues of the arm to the artery wall. To determine under what condit ions this occurs, analyses are presented assuming the arm to be a rotat ional ly symmetric, incompressible sol id cylinder acted upon by various cuf f pressure fields. The results indicate that the pressure appl ied to the artery wal l is markedly inf luenced by longi tud ina l mot ion of the arm tissue, which must be constrained to have an accurate pressure transmission. I t is shown that a wide cuff does effectively accomplish this under its central region. The analyses agree with experiments in which indirect and direct blood-pressure measurements were made and most o f the cl inical observations of others, However, the claim that "if the cuf f is too wide, the reading w i l l be erroneously low" is not indicated in the analyt ical solut ion and has not been observed in the authors" experiments. These analyt ical and experimental results were used to establish criteria for the design of appropriate occluding cuffs. Based upon these criteria, cuffs for cl inical use have been produced from a plastic f i lm in a variety o f lengths and widths.

Keywords--Blood, Doppler effects, Pressure measurement

1 Introduction THIS REPORT deals with the criteria to be used in the choice of an occluding cuff and the design and con- struction of a new cuff; one phase of an investigation into the development of a clinically viable technique to be used in the noninvasive determination of blood pressure in infants and children (ALEXANDER e t al., 1972). The most commonly used method of indirect blood-pressure determination is the auscultatory method using the standard sphygmomanometer. In this method, an occlusive cuff is placed on the upper arm and inflated until the arterial pulse distal to the cuff is obliterated. The cuff is then slowly deflated. The onset of Korotkoff sounds serves as a marker of the peak systolic pressure and the cessation, or muffling, of sounds is regarded as an indication of the end-diastolic pressure.

There are, however, a number of sources of error in this technique. These errors have been broadly classified in the report of the subcommittee of the postgraduate education committee of the American Heart Association (KIRKENDALL e t al., 1967). Some of the more common of these errors are:

(i) inaudibility of Korotkoff sounds owing to low frequency or low amplitude

(ii) poor discrimination criteria of diastole

(iii) deflation too rapid

(iv) use of an inaccurate manometer

First received 13th November 1975 and in final form 12th April 1976

(v) heavy pressure on the pickup head (vi) bladder pressure not accurately transmitted to

the arterial wall. Most of these error sources have been the subject of investigations in our laboratory (BALAS et al., 1972; COHEN et aL, 1973). This report is devoted to point (vi) only, the transmission of bladder pressure to the artery wall. It has been stated that 'The chief source of error . . . (in the determination of blood pressure in infants and c h i l d l e n ) . . , arises from the selection of a poorly supported or inappropriately sized cuff' (KIRKENDALL et al., 1967).

To determine the magnitude of the error encountered with commercially available sphygmomanometer cuff-bladder assemblies, a number of different types have been evaluated during cardiac catheterisation. With a catheter dwelling in the subclavian artery, systolic blood pressure has been measured indirectly using a Doppler ultrasound detector to sense the onset of arterial vibrations and blood flow, the sources of the Korotkoff sounds, in the brachial artery just distal to the cuff. The cuff bladder and intra-arterial pressure signals were sensed by strain-gauge pressure transducers. The two pressures, the Doppler ultrasound signal and the e.c.g, are all simultaneously recorded on an oscillo- graphic recorder. A typical recorder output at the sensing of peak systolic pressure is shown in Fig. I. This illustrates the type of cuff error randomly encountered in sphygmomanometry. A standard commercially available cuff-bladder assembly of

2 Medical & Biological Engineering & Computing January 1977

appropriate dimensions, based upon the American Heart Association criteria (KIRKENDALL et al., 1967), was used on this 6-year-old patient. The bladder, or indirect, pressure at the first Doppler signal is

approximately 20 mm Hg higher than the simultaneously recorded intravascular pressure.

Fig. 2 is a plot of indirect against direct blood- pressure determinations derived from 31 patients,

Fig. 1 Peak systofic blood-pressure determination with a commercially available cuff

140I ~-1'29-193 . / / /

130

line of

A A

I

E E e" 110

P n lOC

A zx ~

a /

9o4 rpJ/ "3mm HI error l imits

80 v / I I l I I I 80 90 100 110 120 130 140

subclavian pressure, ram Hg

Fig. 2 Comparison of indirect and direct pressures for 31 blood-pressure determinations with commercially available cuffs

ranging in age from 1�89 years to 43 years, in the manner shown in Fig. 1. The centre diagonal is the line of identity. Approximately one-half of the patients show inaccurately-high indirect pressures. Errors of 10 to 20 % are frequently encountered. We have therefore established as our first priority the determination of the conditions necessary for the accurate transmission of bladder pressure to the artery wall and to design a blood-pressure cuff- bladder assembly that can be assured of satisfying those conditions.

2 T h e o r e t i c a l a n a l y s e s a n d c o n f i r m i n g e x p e r i m e n t a t i o n

It has been previously reported (SIMPSON et al., 1965; KARVONEN, 1962) that when an occluding cuff that is either too narrow or too short is employed, the result is an erroneously-high blood-pressure reading. This 'small cuff effect' appears to be a problem encountered more frequently in infants than in adults (HANSEN and STICKLER, 1966; Moss and ADAMS, 1965). It has also been reported that, ' if it (the cuff) is too wide, the reading will be erroneously low' (KIRKENDALL et al., 1967). To establish an analytical basis for these observations, two analyses were performed to investigate the mode of transmission of bladder pressure to the artery wall. First, a 2-dimensional analysis was performed to ascertain the role of longitudinal tissue motion in the establish- ment of the pressure field in an occluded arm. Then

Medical & Biological Engineering & Computing January 1977 3

a 3-dimensional analysis was performed to demon- Not ing that strate the relationship of the cuff-width/arm- diameter ratio to the accuracy of transmission of du bladder pressure to the artery wall. ep = . . . . . . . . . ( 8 )

2 . 1 2 -d imens iona l analys is

It is assumed that the a rm can be approximated as a long, rotat ional ly symmetric cylinder o f a linearly elastic, incompressible material .with a rigid inclusion of radius a (bone). At the outer radius a uniform pressure field p is applied. It is desired to determine under what circumstances the hydrostatic pressure (the dilitational stress com- ponent) inside the arm is also p. Since the brachial artery is not strongly at tached to adjacent structures, it appears reasonable to assume that the cuff pressure is transferred to the artery wall via the hydrostatic pressure. This analysis is essentially the Lam6 problem for a thick cylinder with the govern- ing differential equat ion

v 4 q ' = 0 . . . . . . . . . ( 1 )

where W is the Airy stress function, with the boundary conditions,

ap(r) = p . . . . . . . . (2)

and

u(a) = 0 . . . . . . . . . (3)

where p is the bladder pressure, p is the radial direction co-ordinate, 0 is the angular co-ordinate, z is the longitudinal co-ordinate, r is the radius of the arm, a is the radius of the bone, trp is the radial direction stress and u is the radial displacement. The hydrostat ic pressure field

p ~ �89 . . . . . . . (4)

is determined with two different extreme cylinder-end condit ions; (a) completely free longitudinal mot ion (plane stress), a~ = 0, and (b) completely constrained longitudinal motion, e z - 0. where ez is the longitudinal strain.

The general solution to eqn. 1 is

- C z p 2 1 n p + C 2 p 2 + C a . l n p + C , , . (5)

with the stresses defined as

1 dq s op Cz (1 + 2 lnp) + 2C2 q- (73

p dp p2" (6)

and

C3 d2~xl C1(3+21np)+2C2- p2 (7) ~r o -- do ~

where Ca, C2 and Ca are constants to be estab~ lished from the boundary and end conditions.

and

. . . . . . . . . (9)

the constants are found to be, for the case of free longitudinal mot ion (az = 0)

C1 = 0 . . . . . . . . . (10)

C 2 - - r 2 p(1 + V)

/.2 2 a 2 [ ( 1 - v ) + ~ (1 +v)]

(11)

and

- r 2 p ( l - v ) Ca = . . . . . (12)

/.2 ( l - v ) + ~ (1-q-v)

where v is the Poisson ratio. Substituting for C1, C2 and Ca f rom eqns. 10, 11 and 12 in eqns. 6 and 7, and then substituting for the stresses in eqn. 4, yields

- p ( 1 - v )

p . . . . (13) /'2

3 [ ( 1 - v ) + ~ - ( l + v ) ]

for the hydrostat ic pressure. Setting v = 0.5 for an incompressible material and

r/a "~ 4 in eqn. 13 causes

i5 = - ~ p . . . . . . . . . . (14)

Therefore, for the extreme condit ion of completely free longitudinal mot ion of the arm tissues, a 50% error can be incurred in the measurement of blood pressure.

F o r the opposite extreme condition, completely constrained longitudinal mot ion (ez = 0), the constants are found to be

Cx = 0 . . . . . . . . . . (15)

- r 2 p(1 + v)

C2 = (16) i.2

2a 2 [(1 - v - 2v 2) + - ~ - (1 + v)]


and

-- r 2 p ( 1 - v ~ 2v 2) Ca . . . . (17)

r 2 (1 - v - 2v 2) + ~ - (1 + v)

Again, substituting into eqns. 4, 6 and 7 yields, for v = 0.5,

p = - p . . . . . . . . . (18)

Consequently, if longitudinal motion is completely constrained, no blood-pressure-measurement error results, owing to a poor transmission of pressure to the artery wall.

These results are only qualitatively correct in that an approximate constitutive relationship has been used for the arm tissue and a 2-dimensional analysis has been performed. However, they do indicate the role that longitudinal tissue motion should play in the transmission of bladder pressure to the artery wall. To verify this role, experiments were performed in which the cuff/arm interface wag lubricated to facilitate longitudinal tissue motion.

2 .2 Effect o f lubricating the cuff/arm interface

It was reasoned that in situations where the occluding cuff is just wide enough to transmit pressure accurately to the artery wall, lubrication of the cuff/arm interface should allow enough longitudinal tissue motion to then cause measurement errors. Consequently, an experiment was devised during which indirect blood-pressure measurements were made simultaneously on both arms using adult size 120 x 230 mm blood-pressure cuffs.

Table 1. Effect of lubricating the cuff/arm interface

The Korotkoff;sounds were sensed with a crystal microphone. The:three signals, bladder pressure in both cuffs a n d the left- and right-arm Korotkoff sounds, were simultaneously recorded on a Honeywell Visicorder. The systolic and diastolic pressure levels were later determined from an examination of the output to avoid observer errors or bias. In testing each individual, a number of tests were first performed without lubrication to establish that the left- and right-arm pressures were comparable. Then, after placin(g a lubricated plastic sheet between the cuff and tfi.e left arm, the test was repeated. The results of this experiment performed on five adult males are presented in Table 1.

The American Heart Association committee has recommended that the width of the blood-pressure cuff be 20% greater than the arm diameter to avoid the 'small-cuff effect' (KIRKENDALL e t al., 1967). Since a 120mm wide cuff was used in these tests, the small-cuff effect should be in evidence in the measurements taken on subject GT who has an arm diameter of 111 mm. Lubrication should cause an increase in the pressures measured at his left arm compared to those determined from his right arm. An examination of the tabulated results indicates a 5 to 10 mm Hg pressure jump induced by the lubrication. Subjects MC and FV both have 95 mm wide arms. However, the arms of FV were much more muscular than those of MC. MC,s pressure measurement appears to be affecte d by the lubrication while the measurements from FV are unaffected. Most probably, the softer arm tissue of MC can shear more easily and sustain a greater longitudinal motion than can the muscular arm

Subject Test number Arm diameter mm

Indirect pressure Left-arm Right arm Left arm lubrication

GT 1 111 2 3 4 5

MC 1 95 2 3 4 5

FV 3 95 5 6

PB 1 85 2 3

EL 1, 80 2 3 4

124/72 124/68 118/74 116/70 131/80 12&/76 128/73 132/78 124/75 135/85 104/80 104/80 122/80 120/80 122/ 130/ 125/88 133/98 124/88 130/96 114/70 114/70 108/66 108/70 114/72 114/72 126/65 124/64 126/62 1 24/62 126/66 126/66 125/ 123/ 119/72 119/76 121/75 121/80

n o

no no yes yes n o

n o

yes yes yes n o

yes yes n o

n o

. : yes n o

n o

yes 123/75 123/75 ye s

i i

Medical & Biological Engineering & Comput ing January 1977 5

tissue of FV. The last two subjects, PB and EL, both have narrow muscular arms. Their measured pressures were relatively unaffected by the lubrication.

It appears that this series of experiments is in agreement with the analysis of Sub-section 2.1 above. However, to provide a realistic analytical basis to the phenomena of the small- and wide-cuff effects, it is necessary to perform a 3-dimensional analysis in which the cuff width enters as a parameter.

2.3 3-dimensional analysis

It is again assumed that the arm is a rotationally symmetric cylinder of a linearly elastic, incompressible material. For the purposes of mathematical simplicity, the bone is neglected and the radial stress ap at the cylinder centre is taken as an indication of the accurate transmission of cuff pressure; the reasoning being that, if trp at the axis is still comparable with the cuff pressure p, then certainly the pressure is transmitted faithfully to an artery that is closer to the arm periphery. The pressure field applied to this cylinder is given by

[ p f o r [ z I < b r p ( z ) = [ 0 f o r [ z I > b , - " . . . . . (19)

corresponding to a cuff of width 2br with the z co-ordinate originating under the centre of the cuff. The quantity b is the ratio of the cuff width to the arm diameter.

The problem posed in this section is that of solving the equilibrium equations of the 3-dimensional theory of elasticity for this cylinder with the boundary conditions

trp(p, z) = - p(z), ro~(p, z) = 0 for p = r (20)

in order to evaluate trp(0, z) for z < br. This problem has been previously treated by LURE (1964) by solving the equations in t e rms of displacements in the form due to PAPKOVICH (1932) using a Fourier integral representation and by BARTON (1941) using a Fourier-series representation. The Papkovich solution has the general form

8 (pBp + zB: + Bo) u = 4 ( 1 - v )Bp- - ~

Making a transformation of co-ordinates to replace p and z by the dimensionless variables

x = p/r, ~ = z/r . . . . . . . (23)

it is found that, after expressing p(r by the Fourier integral

P(~)= / p(f l)cosf l~dfl . . . . . (24) , /

0

where

8 w = 4(1 - v ) G - "-z- (pBp+zB:+Bo) .

cz

2p sin fib p ( f l ) -

n f l . . . . . . . (25)

the displacements become

- p r u(x, ~) = ~ ~. [2(1 - v ) / d D / ~ ( ~ x )

0

I I sin fib + f l l o ( f l ) / l ( # x ) - fix x(fl) o ( f l x ) ] ~ cos fl~dfl

(26)

and

- p r f w(x, ~) = ~ [2(1 - v)h (/Dlo(flx) 0

sin ~b + ~xl ~(B)I, (fix) - f l l o (B) Io ( f l x ) ] -~ -~ ) sin ]?~dfl

(27)

where

~e(D = f l Z [ / o ~ ( D - / d ( D ] - 2 ( 1 - v ) I ~ 2 ( D . ( 2 8 )

and I~ and Io are the modified Bessel functions and G is the shear modulus. Upon evaluation of the above integrals, the radial stress at the centre trp(0, ~) is found to be

(21) qp(0, ~) 1 v . - P - l+vJ4(~, b)+ -]--~vja(~, b) (29)

(22) where, under the cuff (b > r

1 + v ~ A(k ~ [exp(--g~ r cos y~(b+~) where u and w are the radial and longitudinal displacements, respectively; and Bz, Bp and Bo are harmonic functions (they satisfy Laplace's equation). Since neither Lure nor Barton have treated incompressible materials or presented their results in a form suitable for our purposes, the analysis has been re-evaluated following the solution of Lure.

+ exp(6s ~) cos ys(b - ~)]

+ B~ (k) [ exp ( - gs ~) sin y~(b + ~)

+ exp (~ ~) sin y,(b - ~)] exp ( - G b) . (30)


with 7~ + i5~ = fl, being the roots of the equation

~l'(fl) = 0 . . . . . . . . . (31)

and

As(a ) _ iBs(3) _ 41a(fl~) (32) ~ , ( f l , ) . . . . . .

As(a )_ iBs(4) _ 2fl, Io(flO Wl(f l , )

. . . . . (33)

d ' V ' ( f l ) = , , , [ ' V ( f l ) ]

a p . . . . . . (34)

For v = 0.5, eqn. 29 is evaluated for b = 0.2, 0.5, 1.0, 1.2, 1.5 and 2.0. The results of these calculations are shown in Fig. 3. It is found that for all cuff widths less than 1-2 times the diameter of the arm, the possibility exists of a measurement error due to poor transmission of bladder pressure.

2br ---I

r~ ) _ _ _

TTT TTITTTTT

10

E b o.8

O6 0 u

O-Zl

;~ o.2 "o ?

c

6p(O,,r

I I I I

0'8 i

1"6

appears to be in direct contradiction to the previously quoted claim that, ' if it (the cuff) is too wide, the reading will be erroneously low' (KIRKENDALL et al., 1967). Experiments performed during cardiac catheterisations (reported in Section 3 below), in which intra-arterial and indirect pressures were determined for various cuff sizes, have indicated that the widest cuff appears to yield the most accurate indirect pressure determinations. It is possible that the previously reported erroneously low readings are signal pickup related rather than cuff related.

3 Design and preliminary evaluation of an improved blood-pressure cuff

3.1 Design and fabrication o f a blood-pressure cuf f

The results of the analyses of Section 2 above and the experimental evidence of the authors and other investigators have been used to establish basic design criteria for a blood-pressure cuff. These are: (i) that good friction contact must be maintained between the cuff and the skin to aid in the constraint of longitudinal tissue motion and (ii) the cuff must be wide enough to accurately transmit pressure to the artery. Additionally, it has been found that if the cuff bladder does not completely encircle the arm, the resulting nonuniform cuff pressure can be an additional source of measurement error, depending upon the depth and location of the artery. This has been previously clinically confirmed by K~NG (1967) who found falsely high blood-pressure readings when the bladder failed to encircle the arm (approximately 12 mm Hg error in systolic and 8 mm Hg in diastolic pressures when measured by a standard sized cuff on a moderately obese arm). Consequently, a third design criteria has been added; (iii) that the cuff bladder should completely encircle the arm.

For hospital use, it is desirable to dedicate a cuff to each patient to avoid crosscontamination. This is especially important in the infant nursery, intensive care and surgery. Consequently, it is essential that the

plastic f~m

clot h 7 ad hesive ~ '

0 0-4 1-2 2 0 L. / nondimensional centre- l ine co-omlinate 12r

Fig. 3 Radial stress at lhe arm axis under an occluding T ~ .... cuff I

U w This result is in agreement with the clinical | observations previously reported (KmKENDALL et al., 1967). However, for all cuff widths greater than 1.2 times the diameter of the arm, the analysis indicates that the pressure is accurately transmitted to all depths of the arm under the centre of the cuff as well as some region out from the centre. Under no circumstance is the pressure field ever higher than the cuff pressure. Consequently, the so-called wide-cuff effect is not indicated. This

heat seals r

cuff bladder

inflation tube

T= LI4 W= 1"2Lilt

Fig. 4 New blood-pressure cuff


cuff assembly can be produced fairly inexpensively in quantity. This latter characteristic also makes it possible to satisfy criteria (ii) and (iii) by making available a series of cuffs in various lengths and widths. Upon careful consideration of many materials and designs, it was finally decided to produce cuffs of a plastic film in the 1-piece unit shown schematically in Fig. 4.

In this design, the cuff and the bladder are one integral unit composed of an airtight bladder section connected to a noninflatable tab that is used to secure the bladder around the arm. A thin cloth is laminated to the inner (arm) side of the bladder to protect the skin from damage yet still allow for a good friction contact between the cuff and the arm. The inflation tube is a plastic semirigid tube that is sealed into the cuff during the bladder sealing. The adhesive securing tab has a length of one-quarter of the bladder length. The contact adhesive, which is protected by a paper strip until use, is pressed onto the backside of the bladder area after encircling the arm, wrapping at least one-quarter of the way around the arm. This makes for a very secure yet easy application of the cuff to the arm. The bladder length to width ratio is planned to be ~r/1" 2, making for a cuff whose bladder width is at least 1.2 times the arm diameter if the bladder encircles the arm. If the bladder does not completely encircle the arm, the cuff cannot be secured since the adhesive will not adhere to the skin. This provides for a relatively fool- proof device. If the cuff bladder is not wide enough to yield an accurate pressure measurement, it cannot

be secured on the arm. The small-cuff effect is not possible with this cuff design.

3.2 Prelim&ary evaluation of the cuffs A series of cuffs in a number of sizes ranging from

30 x 90 mm to 170 x 450 mm was produced. They have been evaluated during cardiac catheterisation. Fig. 5 shows the recorder output obtained during a blood-pressure determination of the same child whose determination with a standard commercial cuff is shown in Fig. 1. This 70 x 150 mm plastic cuff completely encircles the child's arm yielding an indirect systolic determination within 3 mm Hg of the directly measured value. 3 m m H g is the approximate experimental error to be expected from the recording and data transcribing systems. Fig. 6 is a measurement taken on the same child with a 90 x 180 mm plastic cuff, the widest cuff that could be properly applied to this arm. The indirectly determined systolic pressure is identical to the intra- arterial systole. It should be noted, as was predicted in Section 2, that the wide-cuff effect is not indicated.

To date, aver 50 studies have been performed using a number of cuff sizes where possible. The results of these studies, performed on patients ranging in age from l . 5 to 43 years, are summarised in Fig. 7, a graph of indirect against direct systolic pressures obtained with cuffs whose width/arm- diameter ratios varied from 1" 22 to 2" 36. The heavy diagonal line is the line of identity, and the lighter lines on either side represent the 3 mm Hg error limits. The few points that fall above the 3 mm line

Fig. 5 Systolic blood-pressure determination with a 70 x 150 mm plastic cuff on a six-year-old chi ld


were all obtained with cuffs which just satisfied the American Heart Association recommendations for cuff-width/arm-diameter ratio. The more accurate results, obtained with the wider cuffs, all fall within 3 mm Hg of the directly determined systolic pressures.

/ / / 130I- line of

T

E E

110

tO

0

l o o P ._

90

"*3mm Hg error limits

80 90 100 110 120 130 140 subclavian pressure, rnm Hg

Fig. 6 Comparison of indirect and direct pressures for 55 blood-pressure determinations with plastic cuffs

Conclusions

Through the use of theoretical analyses and cxperimental evidence, the means by which cuff pressure is transmitted to the brachial artery during an indirect blood-pressure determination have been investigated. On the basis of these investigations, design criteria for a blood pressure cuff have been established and a new blood-pressure cuff has been constructed and tested. Accurate peak-systolic- pressure values have been obtained when the cuff is used with a Doppler ultrasound detector. Since the Korotkoff sounds are often inaudible in infants, it has been found that the Doppler ultrasound technique is the best rr.ethod of detecting the arterial wall vibrations and brachial blood flow. This phase of the development of a clinically useful technique for the non-invasive determination of blood pressure in infants and children has resulted in the development of a new patient-dedicated blood-pressure cuff that is presently undergoing clinical trails.

Acknowledgment--This work has been supported in part by the Monmouth County, New Jersey Chapter of the New Jersey Affiliate, American Heart Association, through grant GR72-11.

References ALEXANDER, H., COHEN, M. L. and STEINFELD, L. (1972)

The measurement of blood pressure in neonates: The criteria in the choice of an occluding cuff. Proceedings of the 25th Annual Conference on Engineering in Medicine & Biology, 109.

Fig, 7 Systofic blood-pressure determination with a 90 x 180 mm plastic cuff on a six-year-old child


BALAS, C., ALEXANDER, H., COHEN, M. L. and BOUR- DELLE, P. (1972) A mechanical blood pressure analog. Proceedings of the annual meeting of the Association for the Advancement of Medical Instrumentation, April.

BARTON, M. V. (1941) The circular cylinder with a band of uniform pressure on a finite length of the surface. J. App. Mech. 97-104, September.

COHEN, M. L., ALEXANDER, H. and STEINFELD, L. (1973) A hydro-mechanical analog for examining the origins of Korotkoff sounds. Proceedings of the 10th Inter- national Conference for Medical & Biological Engin- eering.

HANSEN, R. L. and STICKLER, G. B. 0966) The 'non- hypertension' or 'small-cuff' syndrome. Clinical Pediatrics 5, 579-580.

KARVONEN, M. J. 0962) Effect of sphygmomanometer cuff size on blood pressure measurement. Bulletin of the World Health Organization 27, 805-808.

KING, G. E. (1967) Errors in clinical measurement of blood pressure in obesity. Clin. Sci. 32, 223-237

KIRKENDALL, W. M., BURTON, A. C., EPSTEIN, F. H. and PREIS, E. O. (1967) Recommendations for human blood pressure determination by sphygmomanometers: Report of a subcommittee of the Postgraduate Educa- tion Committee, American Heart Association. Circula- tion 36, 980-988.

LURE, A. I. (1964) Three-dimensional problems of the theory of elasticity. Chap. 7, section 6, 404-415, Interscience.

Moss, A. J. and ADAMS, F. H. (1965) Auscultatory and intra-arterial pressure: A comparison in children with special reference to cuff width. J. Pediatrics 66, 1094-1097

PAPKOVlCH, P. F. (1932) Solution g6n6rale des 6quations differentielles fondamentales d'61asticit6, exprim6e par trois fonctions harmonique, Comptes Rendue, Aca- d~mie des Sciences (Paris) 195, 513.

SIMPSON, J., JAMIESON, G., DICKHAUS, D. and GROVER, R. (1965) Effect of size of cuff bladder on accuracy of measurement of indirect blood pressure. Amer. Heart J. 70, 208-215.

Cri t6re gouvernant le choix d'un brassard occlu pour la mesure de la pression du sang

Sommaire--Pour qu'une m6thode sphygmomanom6trique de mesure indirecte de la pression sanguine puisse ~.tre pr6cise, le bracelet doit fonctionner de telle faqon que la pression intra-vessie soit toujours la m6me que la pression exerc6e par les tissus du bras sur la parDi de l'art6re. Pour d6terminer dans quelles conditions ceci a lieu, les analyses sont pr6sent6es en supposant que le bras soit un cylindre plein incompressible sym6trique en rotation subissant l'effet de diff6rents champs de pression du bracelet. Les r6sultats indiquent que la pression exercde sur la parDi de l'art6re est nettement influenc6e par le mouvement longitudinal du tissu du bras qu'on doit contraindre pour obtenir une transmission pr6cise de la pression. On voit que ceci est effectivement r6alis6 sous la partie centrale d 'un bracelet large. Les analyses s'accordent avec les exp6riences of a on a fait des mesures directes et indirectes de la pression sanguine et avec la plupart des observations cliniques faites ailleurs. Toutefois, la prdtention qui 'si le bracelet est trop large, la lecture sera erron6ment faible' n'est pas indiqu6e dans la solution analytique et n 'a pas 6t6 observ6e pendant les exp6riences de l'auteur. Ces r6sultats analytiques et exp6rimentaux ont servi /~ 6tablir des crit6res pour l'6tude de bracelets occluants appropri6s. Sur la base de ces crit6res, on a r6alis6 des bracelets pour utilisation clinique dans du film plastique de diff6rentes longueurs et largeurs.

Die Kri ter ien bei der Wahl einer Okklus ivmanschet te zur indirekten Messung des Blutdrucks

Zusammenfassung--Wenn Pin Verfahren zur Blutdruckmessung ftir die indirekte Blutdruckmessung genau spin soll, mul3 die Manschette so funktionieren, dab der Druck in der Blase immer der gleiche ist wie der durch die Armgewebe auf die Arterienwand ausgeiibte. Um festzustellen, unter welchen

Bedingungen dies auftritt, werden Analysen vorgelegt, die annehmen, dab es sichbei dem Arm um einen symmetrisch runden, nicht zusammendriickbaren, massiven Zylinder handelt, auf den verschie- dene Manschettendruckfelder wirken. Die Ergebnisse sprechen dafiir, dab der auf die Arterienwand angewandte Druck durch die L~ingsbewegung des Armgewebes wesentlich beeinflul~t wird, das eingeengt werden muf5, um den Druck genau zu iibertragen. Es wird gezeigt, dab dies mit einer weiten Manschette im Mittelbereich erzielt wird. Die Analysen stimmen mit Experimenten iiberein, bei denen indirekte und direkte Blutdruckmessungen vorgenommen wurden und mit den meisten klinischen Beobachtungen von anderen. Die Behauptung jedoch, dab 'wenn die Manschette zu welt ist, die Ablesung irrtiimlich niedrig ist' ist in der analytischen L/Ssung nicht angegeben und wurde in den Experimenten des Verfassers nicht beobachtet. Diese analytischen und experimentellen Ergeb- nisse wurden zur Aufstellung der Kriterien fiir die Konstruktion yon entsprechend einschlieBenden Manschetten verwendet. Aufgrund dieser Kritieren wurden Manschetten ftir den klinischen Gebrauch aus Plastikfolie in mehreren L[ingen und Breiten hergestellt.


criteria in the choice of an occluding cuff for the indirect measurement of blood pressure

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