Drugs 11 (Suppl. 1): 48-57 (19761 © ADIS Press 1976

Session III: Measurement of Blood Pressure and Pre-Treatment Work-Up Chairman: Professor R. R.H. Lovell (Melbourne)

New Instruments for Measuring Blood Pressure

D. R. Labarthe Department of Medical Statistics and Epidemiology, Mayo Clinic, Rochester

Summary

The development of the conventional indirect method of blood pressure measurement essentially complete by 1905, 70 years ago. The method has certain shortcomings, but these can be offset to a large degree by control over conditions of measurement, provision of proper apparatus, and intensive training of observers. Still, there are potential advantages which might be met by an acceptable automated device. An experimental evaluation of five such devices led to rejection of each of them on grounds of inadequate measurement performance, mechanical failures, or both. Only the Random-Zero device (Hawksley), among the instruments tested, gave good performance in comparison with the conventional method and \4.WlS free of serious mechanical disadvantages. Evaluation of new devices will continue to be of great importance, and proposed guidelines for such studies are reviewed. \4.WlS

1. Introduction The fact that this brief conference, giving consideration to a number of major issues about hypertension, includes specific attention to blood pressure measurement itself is perhaps one of the most important observations to be noted on the subject. Measurement of blood pressure is so commonplace, and its validity is so often taken for granted, that opportunities to examine the matter critically are infrequent. We have much to learn if we are to see real

achievements of practical value in the technology of blood pressure measurement - a field where, in the view of many, progress has been disappointingly slow. I would like in this paper to discuss the deliberations of a group of investigators in the US who, early in 1972, were obliged to reach agreement on a method of blood pressure measurement for a massive, multi-centre, collaborative trial of detection and management of hypertension in total communities - the Hypertension Detection and Follow-up Program, or HDFP, supported by the National Institutes of Health (Remington, 1973). For the HDFP, more than 150,000 adults

New instruments for measuring BP

were to be screened and, ultimately, more than 11,000 hypertensives enrolled in one or the other of two long-term programmes of follow-up. Clearly, a programme of such magnitude and likely importance must rest on the soundest measurement techniques available within practical limits. Drs Remington and Hawkins and I, working in the National Coordinating Center of the HDFP in Houston, Texas, accepted responsibility for conducting a review of available methods and presenting our recommendations to the Steering Committee of the Program. We believed it was important to consider the conventional technique, applied in a standardised way as recommended in publications of the American Heart Association (Kirkendall et al., 1967). We then identified six alternative devices with various features expected to have advantages over the conventional technique, and we conducted a formal evaluation of their measurement performance and related properties. We presented our recommendations for consideration by the HDFP Steering Committee as a whole, and went on to develop the full details in an extensive Manual Of Operations for the instruction of all blood pressure observers, their supervisors, and persons responsible for maintenance of the instruments in use. Our evaluation was necessarily limited in scope and since 1972 several new instruments for measuring blood pressure have been devised. We have continued to be interested in these developments and, although we have conducted no further experimental studies on these newest devices, our work has contributed to two new documents addressed to the problem of evaluating blood pressure measurement techniques. I will comment, in closing, on a recent report of the American Heart Association on this subject and on the manuscript drafted by a Task Force convened by the National Heart and Lung Institute, and soon to be released, which catalogues many of the devices commercially available in the US and offers criteria for their evaluation (Feinlelb et al., 1974; US Dept. HEW, 1976).

49

2. The Conventional Technique of Blood Pressure Measurement - Its Development, Limitations, and Possibilities for Improvement The earliest attempts to measure blood pressure are attributed to Hales, who conducted his experiments on large animals nearly 250 years ago utilising direct, intra-arterial cannulation (Geddes, 1970). Despite very impressive refinements in intra-arterial techniques, there are many practical considerations disfavouring arterial puncture and there is of course increasing favour, in principle, for 'non-invasive' techniques in all areas of clinical practice and health research. The development of the contemporary method of indirect blood pressure measurement, following on the work of Hales in the early eighteenth century, is doubtless familiar to most. The major advances in technique were those introduced by Poiseuille, who employed the mercury manometer, permitting reduction in scale of the apparatus; by Riva-Rocci, who used an occlusive cuff to control blood flow through the underlying brachial artery; by von Recklinghausen, who standardised the dimensions of the cuff; and by Korotkoff, who in 1905 described the auscultatory phenomena which accompany changes in arterial blood flow beneath the cuff and which can thus be related to the cuff pressure as read from the manometer (Benson, 1973; Geddes, 1970). Thus, the events of over 150 years were required to develop the method which today, 70 years after Korotkoffs contribution, includes the conventional components - the mercury sphygmomanometer, the occlusive cuff, the stethoscope and, far from least important, the observer. This method was very rapidly applied in clinical practice and in research and has become the basis of an extensive body of knowledge regarding the risks associated with successively higher levels of blood pressure. It is important to emphasise that the basis of the whole of our epidemiologic knowledge of blood pressure, and its associated antecedents and sequelae, is the indirect method. The

Symposium on hypertension

direct method has not been applied on a scale permitting equivalent validation, nor is the correspondence between direct and indirect methods clearly established. For these reasons, it is the indirect approach, with the components already noted, which must for now be taken as the standard method of blood pressure measurement (Labarthe et al., 1973; Feinleib et al., 1974; US Dept. HEW, 1976). Yet this standard method is not free of shortcomings. Indeed, it is this fact which has stimulated the development of numerous devices now offered as substitutes for the standard apparatus with its necessarily heavy reliance on the human observer. What then are these shortcomings, and what steps if any can be taken to resolve them? Apart from true moment-to-moment variation in the subject and random measurement error, several sources of systematic error in blood pressure readings by the standard method are commonly recognised (Holland, 1963; Evans and Rose, 1971). These latter errors may be attributed to the conditions of measurement, the nature of the apparatus, and the performance of the observer. Such factors as background noise interfering with perception of Korotkoff sounds, or physical exertion by the subject immediately prior to the measurement, may be regarded as conditions of measurement affecting either the accuracy of the reading or its comparability with readings on other occasions or for other subjects. Both inaccuracy of the manometer owing to mercury loss and improper cuff size in relation to circumference of the arm exemplify potential contributions of the apparatus to measurement error. Observer error may be considered to be of two general types - faults of procedure, such as improper placement of the cuff or excessively rapid cuff deflation, and faults of judgement, such as mis-interpretation or inco-ordination in linking the auscultatory and visual cues necessary for deciding on the systolic and diastolic readings. Fortunately, approaches are available for dealing effectively with most of these difficulties

50

(Kirkendall, 1967). The conditions of measurement can be standardised within practical limits, including the choice of arm, position of the subject, duration of rest before the determination, restriction of immediately prior cigarette smoking, and so forth. Attention to the state of the instrument and availability of cuffs of differing widths suffice to obviate the principal difficulties with the apparatus. Less easily, but with demonstrated effectiveness, observer error can be minimised also. The requirement is a brief but intensive period of training. Observer training is so important a consideration for proper blood pressure determination by the standard technique that at least brief mention of training methods seems mandatory. There are four general requirements for an effective training programme. First, for any specific measurement situation, the need for training and the objectives of the effort must be presented persuasively to the prospective blood pressure observer. Second, some reference standard of 'true' measurements must be adopted and the criteria of acceptable performance stated in relation to that standard. Third, methods and materials for training must be selected and implemented and, fourth, the results of training must be evaluated and presented to the trainee to ensure adequate performance. An ideal method of training has not yet been devised. However, resources are available to provide an effective training programme. The need for training can be demonstrated through discussion and actual participation in a mm exercise, devised by Wilcox, which reveals both inter- and intra-observer disagreement on systolic and diastolic readings (Wilcox, 1961). A reference standard, developed by Rose, is provided by a series of recorded sequences of Korotkoff sounds played back repeatedly in the practice mode by the observers, who are given the correct systolic and diastolic results after an initial practice round (Rose, 1965). A separate series of recorded subjects comprises an independent test mode whose correct values are unknown to the ob·

51

New instruments for measuring BP

Table I. Characteristics of selected devices for measuring blood pressure (after Labarthe et aI., 1973) Characteristics

Arteriosonde 1010

Arteriasonde 1216

Boston Physioautometrics (USMmatic recorder 105)

Diastolic reading capability, phase Based on Korotkoff sounds Permanent record Portable 2 Electric power required Battery capability I nflation rate preset Inflation peak preset Deflation rate preset Auditory dependence Manometer reading required Manometer type

IV No No Yes Yes Yes No No No Yes Yes Aneroid

Unit costs ($US)'

1850

IV No No' No Yes No Yes Yes Yes No Yes Mercurial 2975

IV,V Yes Yes Yes Yes No No No Yes No No Mercurial 1500

Sears (1080)

IV V Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes No No No No' Yes No No No No Aneroid Aneroid 1035

200

RandomZero (Hawksley)

Baumanameter (0300 V-lock)

IV,V Yes No Yes No

IV,V Yes No Yes No

No No Yes Yes Yes Mercurial 325

No No No Yes Yes Mercurial 44

1 Permanent recording obtainable with the Arteriosonde 1216 by addition of a strip chart recorder (model 1508); not tested in this evaluation. 2 Portability judged by weight and casing design only; standard weight of the Arteriosonde 1216 is 40 lb. 3 Deflation rate for the Physiometrics device controlled by a manual knob found to require frequent adjustment, and therefore not considered fixed. 4 Amounts shown do not necessarily reflect costs at volume purchase; costs for additional supplies or equipment (for example, recording charts, conducting gel, stethoscopes) not included.

servers, thus permitting quantitative evaluation of performance. In addition, a detailed written manual for the procedure of actual readings on live subjects can be used to supplement these materials to constitute a programme requiring approximately 10 hours of intensive work. The documented immediate results can be quite satisfactory; long-term performance can be evaluated also (Rose, 1965). To summarise our thinking up to this point, the weight of decades of epidemiologic investigation of blood pressure had been based on the conventional, indirect method. Certain shortcomings in this method had been recognised for a long while, and several of the shortcomings could be controlled wholly or in part by careful attention to the conditions of measurement, the apparatus

itself, and the proper training of observers. Still, the newer devices promised a variety of improvements. Therefore, our next question was, how to evaluate their performance as possible alternatives to the conventional method?

3. Results of an Evaluation of Several Devices We selected for evaluation five partly-automated devices, one modification of the conventional sphygmomanometer, and the standard apparatus (Labarthe et al., 1973). Table I identifies the devices included and lists certain important features of each. The Arteriosonde 1010 was an ultrasound device which converted the signal to resemble audible Korotkoff sounds conveyed to

Symposium on hypertension

52

the observer by a headset. Pressures were read directly from an aneroid manometer. The Arteriosonde 1216 was operated on the ultrasound principle, but internal circuitry controlled the falling mercury in two parallel manometers, such that one column of mercury would come to rest at the systolic pressure and the other at the diastolic pressure. The Boston Automatic Recorder detected Korotkoff sounds by microphone, converted them to mechanical impulse spikes recorded on electrocardiographic paper by a heated stylus, and calibrated the resulting tracing by impulses generated by electrodes at fixed points on the manometer column. The Physiometrics device similarly converted sounds detected by microphone to mechanical impulses, in this instance recorded by an ink stylus on a rotating disk, which was graduated to permit reading of the pressures. The Sears device converted the sounds to impulses by a hammer on pressure-sensitive paper. The Random-Zero device was essentially an ordinary mercury sphygmomanometer, modified to obscure to the observer, until the end of a completed reading, the actual values of pressure observed (Wright and Dore, 1970). This device was included in portions of the evaluation, and the mercury sphygmomanometer, employed by trained observers, was taken as the standard. Two units of each device were compared as part of the assessment. There were four criteria: First was general suitability for the uses intended - screening and

Co E. 07 F, G, B. A2

A. Go E. C2 B7 F, 05

B2 A, C, G7 D. Eo F.

F7 D. Ao B. E2 G, C,

0, B, G2 A. F. C. E7

E, F2 B, Do C. A7 G.

G. C7 F. E, A, O2 B.

Fig. 1. 7 by 7 Graeco-Latin square design (1 st square). Rows across = participants; columns down = order of observation; Latin letters = observers; subscripts = devices.

Reading order

Right arm Left arm

1st

2nd

Specimen 1 Specimen 2

Specimen 2 Specimen 1

Fig. 2. Typical cell of 7 by 7 Graeco-Latin square

follow-up of large numbers of persons in home and outpatient settings - a criterion which was satisfied by all of the devices tested. The second criterion was reliability of operation - freedom from mechanical failure - by which both specimens of three automated devices and one specimen of each of the two other automated devices, were found unsatisfactory. The third and fourth criteria, two aspects of measurement performance, required more elaborate evaluation and warrant more detailed discussion. Seven devices were to be tested Simultaneously, and the experimental design judged most suitable was that of a 7 by 7 Graeco-Latin square, illustrated in figure 1. Rows correspond to participants, columns to order of observation, Latin letters to observers and subscripts to devices. Thus, for example, the first participant's first reading, as shown in this figure, was by observer C, using device number 6 (the Random-Zero). Many such squares can be constructed, each with the property that each Latin letter and each subscript occurs once and only once in each row and each column, and that each of the 49 pairs consisting of a specific Latin letter and a specific subscript occurs once and only once. Three such squares were randomly selected, two for the basic experiment and a third for subjects selected for higher than usual blood pressure levels. For each of the 49 cells in each square, four blood pressure readings were recorded, one on each arm with each of the two specimens of each device. A typical cell is shown in fig. 2. The possible sequences - beginning with the right or left arm, using the first or second specimen of a

New instruments for measuring BP

53

Table II. Comparison of other devices with Baumanometer according to Dunnett's procedure, for systolic means (mm Hg) (after labarthe et aI., 1973).

Data

Squares 1 and 2

x

d Critical values Square 3

x d

Critical values

Arteriosonde 1010

Arteriasonde 1216

Boston automatic recorder

Physiometrics (USM-105)

Sears (1OS0)

RandomZero (Hawksley'

Baumanameter (0300)

111.9 100.3 110.7 110.1 -11.71 -0.1 -1.3 -1.9 d' 0.05,144 = 2.66 .J2(33.58'/6 = 8.89

98.0 110.3 112.0 -14.0 1 -1.7 d' 0.01,144 = 3.21 .J2(33.58'/6 = 10.74

122.7 113.22 118.3 1.1 -8.42 -3.3 d' 0.05.72 = 2.70 .J2(37.45'/6 = 9.54

1OS.8 120.9 121 .6 -12.8 1 -0.7 d' 0.01,72 = 3.28 yr-2 (""3=-7.-:":45::7)/=6 = 11.59

118.0 -3.6

1 < 0.01 2 Observations for specimen 2 only.

given device - were assigned randomly to each cell in each of the three 7 by 7 squares. Thus, in this experiment, a participant, observer and machine type would come together in a predetermined order, and the observer would carry out the prescribed sequence of readings for that subject with the two specimens of that machine. Potentially, each replication would thus yield 28 readings for each participant, for each order, and for each observer, and 14 readings for each specimen of each device, for systolic and whichever diastolic readings the devices allowed. Even though incomplete for diastolic readings, the geometry of the design guarantees that the means for machines providing a given end point are balanced across observers, participants and orders. In a second experiment, a series of eight readings were made with each operating specimen of each of the five automated devices for comparison with paired readings on the Baumanometer. Means and variances of available readings on all five automated devices were compared with those on the standard mercury sphygmomanometer. The paired t test was used in evaluating the comparisons between means. The implementation of the experiments proceeded from selection and training of the observers

in the use of each device to recruitment of subjects and actual setting up of the examination stations. In both experiments, the series of readings for each sequence per subject was completed in a single sitting. The readings were separated only by the time required for the recording and for rearranging the device, the subject, or both, to permit the next reading. The results are presented in detail elsewhere and only the highlights can be noted here (Labarthe et al., 1973). First, we pooled all readings for both specimens of each device and compared the mean systolic readings for both specimens of each device with the Baumanometer, or standard mercury sphygmomanometer (table II). For two devices, the Arteriosonde 1216 and the Sears, the mean systolic values were Significantly lower than the standard method, by differences from 8.4 to 14.Omm Hg. Second, the systolic readings for each of the two specimens of each device were compared, except in the second and third replications of the Graeco-Latin square design, where two devices were each represented by only one surviving unit (table III). In general, disagreement between units was in the order of only 2mm Hg but, as before, the Arteriosonde 1216 and Sears device compared poorly with the Baumanometer.

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54

Analogous comparisons among the devices giving a phase IV diastolic reading showed very poor agreement with the Baumanometer for every device except the Random-Zero, and for the Physiometrics the disagreement between units was nearly 5mm Hg (table IV). Similarly, phase V values on the Random-Zero device were quite comparable with those on the Baumanometer but the other devices differed substantially (table V). It should be noted that all of these differences were in the direction of lower diastolic values for the automated devices, generally of the order of lOmm Hg or more below those for the standard technique. The remaining comparisons were made on the results of the experiment providing paired readings between the Baumanometer and each of the automated devices. To summarise these results, all but the Boston Automatic Recorder differed' significantly from the Baumanometer in one or more of the comparisons of mean values for systolic and phase IV and V diastolic blood pressures. Variances of each paired set of readings were also compared and showed consistently favourable results only for the Boston Automatic Recorder.

Unfortunately, as mentioned earlier, all of the automated devices suffered mechanical problems including, for the Boston Automatic Recorder, complete operating failure. Throughout these tests, the Random-Zero device performed well with respect to the blood pressure values observed. Difficulties with the uniform deflation control valve were noted - the deflation rate was not constant over the range of cuff pressures applied - and the volume of mercury to be drawn off into the reservoir at times required as long as 90 seconds at high cuff pressure before deflation could begin. In one such case, marked ecchymosis occurred around the full circumference of the subject's arm beneath the cuff. What was our recommendation on the basis of this evaluation, against our review of the conventional technique? It was our conclusion that none of the automated devices tested was a satisfactory alternative to the conventional method. If adequate training of observers were assured, we believed the only clear improvement which might be realised was use of the Random-Zero device,

Table III. Comparison of devices for measuring blood pressure by Graeco-Latin Square Design, for systolic means (mm Hg) (after Labarthe et aI., 1973)

Square

2 3 Overall

Specimen

Arteriosonde 1010

Arteriosonde 1216

Boston automatic recorder

Physiometrics (USM-105)

Sears (1080)

RandomZero (Hawksley)

Baumanometer (0300)

1 2 1 2 1 2

104.0 106.4 117.7 119.6 120.7 124.7

101.4 92.8 102.4 104.6

107.7 1 104.0

119.4

93.3 89.7 104.9 104.1 110.1 106.1

103.1 102.0 116.7 119.1 119.9 122.0

103.8 105.6 119.9

112.4

104.7 106.7 116.3 112.4 120.0 116.0

1 2 Combined

114.1 116.9 115.5

101.9 3 103.3 102.7

107.7' 113.9 113.5

113.6 111.7 112.6

102.8 100.0 101.4

113.2 114.4 113.8

115.7 115.2 115.4

1 Mean of three observations. 2 No observations due to failure of specimen 1. 3 Mean of 28 observations.

118.3

118~9

123.4 121.0

New instruments for measuring BP

55

Table IV. Comparison of devices for measuring blood pressure by Graeco-Latin Square Design, for diastolic means. Phase I V (mm Hg) (after Labarthe et aI., 1973). Square

2

Specimen Arteriosonde 1010

Arteriosonde 1216

Boston automatic recorder

Physiometrics (USM-105)

RandomZero (Hawksley)

Baumanometer (0300)

1 2

60.9 60.9 66.9 69.1 69.1 63.7

70.7 64.9 65.7 68.3

76.3' 71.9

73.7

77.9

73.1 69.7 77.3 72.3 79.1 73.0

77.1 74.9 79.9 81.6 88.8 89.0

77.9 80.7 85.6 85.7 85.7 91.0

65.6 64.6 65.1

68.23 69.0 68.7

76.3' 75.9 75.9

76.5 71.7 74.1

81.9 81.8 81.8

83.1 85.8

2

3 2 Overall

1 2 Combined

77.9

84.4

1 Mean of three observations. 2 No observations, due to specimen 1 failure. 3 Mean of 28 observations.

with modifications to correct the mechanical difficulties we had experienced. This device offered the advantages of blinding the observer to the actual pressure at the time of each reading, and of making successive readings independent of the observer's knowledge of the preceding readings. These advantages were judged especially valuable for the HDFP, where observers might be under difficult psychological pressures regarding the eligibility of subjects for the Program and management decisions throughout their follow-up period. The final judgement of our Steering Committee was to adopt the use of the conventional technique in a series of three readings for home screening. Persons found hypertensive in the home were invited to special clinics for re-examination. Four readings of blood pressure were recorded in the clinics - the first and third by the conventional technique, and the second and fourth, by the Random-Zero device. All decisions about eligibility and management in the HDFP are based upon the average diastolic pressures at readings 2 and 4.

4. Principles of Evaluation of New Devices While our own decisions for the HDFP have been made and implemented - with well over a million blood pressure readings already performed - we have of course resolved only one particular question of evaluation, at one point in time. If the potentially valuable technical improvements offered by a variety of new devices are to be realised and adopted for the indirect measurement of blood pressure, continued and extended evaluation will be needed. A recent report from the Committee on Criteria and Methods of the Council on Epidemiology, American Heart Association, suggest guidelines for a systematic programme of evaluation for any device proposed for application in screening programmes (Feinleib et al., 1974). While other applications might require modification of these guidelines, it is nonetheless pertinent to review briefly the multiple components of a comprehensive evaluation programme as outlined by the Committee. Five methods of evaluation are indicated, with

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56

the intent that they be regarded as complementary, each contributing importantly to overall appreciation of the assets and limitations of a given device. First, review of the manufacturer's specifications alone should provide important information on several features. For example, dependence upon a fixed cuff size may exclude a device from consideration in a particular instance. Second, laboratory tests are needed to verify certain of these specifications and can be conducted without recourse to actual measurements. Automatic cuff inflation and deflation can be tested in this way. Third, clinical testing is required where observers employ the device for obtaining actual blood pressure readings from participating subjects. At this level, by properly designed experiments, measurement performance can be assessed. Fourth, field tests are required to assess certain aspects of performance of a device, such as the ease of calibration or the need for minor repairs in field situations. Finally, long-term monitoring of a device in field use can provide Table V. Comparison of devices for measuring blood pressure, by Graeco-Latin Square Design, for diastolic means, phase V (mm Hg) (after Labarthe et al., 1973)

Square

2 3 Overall

Speci- Boston' Sears men auto(1 080) matic recorder

Random- Baumanozero meter (Hawk- (0300) sley)

1 2 1 2 1 2

58.1 52.6 66.9 55.7 69.9 65.3

73.7 70.4 77.4 78.7 85.3 85.7

75.6 78.6 81.4 82.0 82.7 87.6

65.0 57.9 61.4

78.8 78.3 78.6

80.0 82.7 81.3

67.0' 63.3 69.3 67.0

1 67.0' 2 66.5 Com- 66.5 bined

1 Mean of three observations. 2 No observations due to failure of specimen 1.

important data in regard to durability, calibration drift and other features. The most recent comprehensive review of the newer instruments for measuring blood pressure was undertaken recently in the United States by a Task Force consultant to the National Heart and Lung Institute (US Dept. HEW, 1976). The report of this review will be a valuable reference document and is expected to become available soon. As in the American Heart Association review, an extensive (and much more specific) list of descriptors was formulated for comparison of the devices now commercially available in the US. Many of the devices for which manufacturers provided information to the Task Force appeared to offer potential advantages in several respects. Permanence of the output through some form of recording device was offered by several units, and general convenience in use might result from special cuffs, automatic inflation and deflation, and other features of certain devices. Chief among the potential advantages were those features which would tend to reduce dependence of the measurement on the human observer and thus reduce the likelihood of either procedural or judgemental errors. It must be remembered, however, that an exchange of machine-dependence for observerdependence does not necessarily result in improved measurement reliability. The rather disappointing results of our own evaluation for the HDFP underscore the merit of this point of caution. 5. Conclusion

The conclusion to be drawn on the basis of our own evaluation, as well as the reviews by the American Heart Association and the Task Force of the National Heart and Lung Institute, is this: While there may be many potential advantages of particular automated devices, it cannot be presumed, with\.lut careful evaluation, that a given device will in fact perform reliably. If measure-

General discussion

57

ment performance is inadequate, this consider- Geddes, L.A.: The direct and indirect measurement of blood pressure (Year Book Medical Publishers, ation must outweigh any of the special convenOlicago 1970). iences offered by certain devices - even if Holland, W.W.: The reduction of observer variability in thorough testing has demonstrated freedom from the measurement of blood pressure; in Pemberton (Ed.), Epidemiology: Reports on Research and critical mechanical failures. Teaching, 1962 (Oxford University Press, London It is important to re-emphasise that indirect 1963). blood pressure measurement requires, foremost, Kirkendall, W.M.; Burton, A.C.; Epstein, F.H. and Freis, attention to the quality of performance. From this E.D.: Recommendations for human blood pressure perspective the standard method, employing the determination by sphygmomanometers. American mercury sphygmomanometer, cuff, stethoscope Heart Association. Circulation 36: 980-988 (1967). and observer should neither be taken for granted labarthe, D.R.; Hawkins, C.M. and Remington, R.D.: Evaluation of performance of selected devices for because of its longstanding and widespread use nor measuring blood pressure. American Journal of Cardiabandoned because of its recognised shortcomings. ology 32: 546-553 (1973). Proper attention to conditions of measurement, Remington, R.D. (for the Hypertension Detection and status of the apparatus and training of observers Followup Program Investigators): The Hypertension Detection and Followup Program (USA); in Epidemican result in measurements of an order of reliology and Prevention of Cardiovascular Diseases, ability which has not to date been shown to INSERM 21: 185-194 (1973). characterise the automated indirect methods. In Rose, G.A.: Standardization of observers in blood presthe evaluation of alternative devices, attention sure measurement. lancet I: 673-674 (1965). should be given to ensure that this high quality of United States Department of Health, Education and Welfare, Task Force on the Assessment of Automated performance is employed as the standard. It is to Indirect Blood Pressure Measuring Devices for Mass be hoped that the continued evaluation of devices Screening: Report (In press, 1976). which promise useful improvements will, in time, Wilcox, J.: Practice Blood Pressure Readings. Film Cataestablish other methods as acceptable or superior log No. M1582, National Medical Audiovisual Center, choices. At present, however, only such technical Atlanta, Georgia (1961). modifications as that illustrated by the Random- Wright, B.M. and Dore, C.F.: A Random-Zero sphygmomanometer. Lancet I: 337 -338 (1970). Zero device appear to offer immediate improvements in indirect blood pressure measurement.

References Benson, H.: Methods of blood pressure recording: 1733-1971; In Onesti, Kim and Moyer (Eds) Hypertension: Mechanisms and Management, The TwentySixth Hahnemann Symposium (Grune and Stratton, New York 1973). Evans, J.G. and Rose, G.: Hypertension. British Medical Bulletin 27: 37-42 (1971). Feinleib, M.; labarthe, D.; Shekelle, R. and Kuller, L.: Criteria for evaluation of blood automated blood pressure measuring devices for use in hypertensive screening programs. A report of the Committee on Criteria and Methods of the Council on Epidemiology, American Heart Association. Orculation 49: 6-11 (1974).

Author's address: Dr D.R. Labarthe, Department of Medical Statistics and Epidemiology, Mayo Clinic, Rochester, Minnesota (USA).

General Discussion (Methods for Measuring Blood Pressure) Prof. Simpson: The problem of course is to know what one really wants the machines to do. We felt that the Rose 'Sphygmomanometer for Epidemiologists' really had a very good principle; that is, it used the human ear which really, in spite of what is said about it, is pretty good and can be trained to be very accurate. The Rose Sphygmomanometer also has the advantage of doing what always has been done, as it were. But the problem with it

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58

is that although it is reliable and rugged, it is rather slow Dr Labarthe: I have not had direct personal experience and inconvenient to use and we felt that the best thing with the aneroid devices other than the one I used to perhaps was to try to use electronics to improve the speed carry in my black bag as a medical student. I think we of performance. We therefore made an electronic version were guided by the prevailing view (which has not to my of this machine and have been using that in our clinic. We knowledge been supported by specific data, but seems are quite pleased with it, although the original version in reasonable) that the aneroid devices - in circumstances which the machine found for each individual patient the where they may be knocked about and subject to blood pressure to which it needed to raise the cuff mechanical problems - were not as reliable. Whether pressure, turned out to be just a little bit slow. This there are data to show that use of an aneroid device may machine also gives you pulse rate which is becoming be in some way superior to the mercury manometer, I do increasingly valuable. Additionally, we tried one that not know. I have never seen such data. Dr R.H. Briant (Auckland): There is a question I patients could carry about with them like the Rembler portable machine based on Sokelows' design. We did not would like to ask before we get tied up too much in find that really too useful, partly because of the sheer electronics. Are we measuring phase IV or phase V amount of work required for training the patients and Korotkoff sounds, because it seems to be very important? handling the whole thing, but of course this type of May I perhaps ask for a show of hands as to who measures instrument has provided very useful data. The final step IV and who measures V, and what do they mean? Prof. Lovell: Shall we take an unbiased reply to that of course is something completely automatic, so that the sounds are interpreted by the machine in some way and froll' the meeting? fA show of hands revealed that about Dr Labarthe has analysed the performance of the various half measured phase IVand half phase V sounds} . Dr Labarthe: Given that split in the vote, I feel instruments available. Prof. Lovell: Dr Labarthe, in general you drew the equally at hazard in coming down on either side. What I distinction between the different sites of use of a can do is to fall back on the wisdom of our Steering machine, whether you are using it in a surveyor in a Committee for the HDFP. The tenor of the discussion consulting room. Could you comment on any need as you suggests that the problem is no re subject to consensus see it, in ordinary consulting room circumstances, for here than it is in the US. I think the debate regarding having anything other than the traditional manometer? phase IV or phase V readings of diastolic pressure was Dr Labarthe: I think the central question is how perhaps the one we persisted in longest, until the time accurately those pressures are recorded in usual practice; came to actually draft the forms and write the manual. I it may well be that some device which removes much of think persons of good intent and goodwill differ strongly the observer error would be advantageous in such a in their opinions on this point and we chose to debate it setting. The alternative is to ensure that observers are in until there was no longer any time for the luxury of fact optimally trained (and periodically re-trained) to debate. The decision in fact for the HDFP was to train ensure that their performance is maintained, although this our observers for the reading of 5th phase or disappearis perhaps very difficult to achieve in practice. Our own ance of sound only. This decision was based on 2 or 3 experience was that the training of persons with prior elements of rationale; first was that in the US studies in clinical background was more difficult than the training epidemiology of blood pressure, it is in fact the 5th phase of inexperienced persons, since the former group have or disappearance of sound which has been employed. This practised their own habits of procedure for some years. is true of the Framingham Study, it is true of the other Therefore, from the standpoint of standardisation, other population studies being summarised now in what we call instruments may be more successful than observer our Pooling Project (which brings together several of the standardisation in this setting, but there are practical prospective studies), and it is true of the US National Health Examination Survey. Beyond that we considered problems in that approach too. Dr F.L. Madill (Launceston): Dr Labarthe, while you the potential ease or difficulty of training the observers were considering all the sophisticated electronic equip- (again, drawing largely on inexperienced people for this ment, did you make any comparisons between the task); that is, whether it might be more difficult to train ordinary mercury manometer and the aneroid type? When to detect muffling than disappearance. Our chief guide in I was an undergraduate we were taught that the mercury that was Prof. Geoffrey Rose, who, as I mentioned earlier, type was the best and that aneroids were most unreliable, has made most valuable contributions to the training of but the Royal Australasian College of General Practi- blood pressure observers. In his judgement there was tioners came out rather strongly a couple of years ago and somewhat greater difficulty in training observers to read said that well maintained aneroid equipment was superior phase IV than phase V. We are in fact trying to persuade the Committee of the American Heart Association which to the ordinary mercury manometer.

General discussion

produces a pamphlet on blood pressure measurement techniques (and tends to reverse its recommendations on the diastolic end point), that it is time now for reversal again and that they should come from 4th phase to 5th phase in the next edition. Prof. Lovell: We settled for phase V in the National Blood Pressure Study in Australia, and I think actually succeeded in converting the British MRC (UK has been traditionally a phase IV country) to phase V and I think they have regretted it ever since. Dr S.N.A. Hunyor (Sydney): I suggest that for epidemiology this is all very nice, but one gets into problems when studying blood pressure in the exercise response or in pregnant patients. Here detecting phase V can be a real bind and on occasions difficult to elicit at all. Prof. Lovell: Can you just tell us why it is a real bind? Dr Hunyor: Because very often phase V may go right down to zero; there may be virtually no disappearance in situations of high cardiac output, particularly in exercise and pregnancy. Certainly in a pregnancy project we are currently involved in in Sydney, we find this in practice as well as in theory. We have to use phase IV but then we lose our base line with regard to morbidity data and all epidemiological evidence that is available. We can of course try to measure both, but phase V is still not very useful in these circumstances. What should one do to cope with this problem? Dr Labarthe: I think it is a problem and one has to adapt to it as best one can in particular circumstances. We tried to be quite clear about the area of application that we are concerned with. I would anticipate that when dealing with patients in a clinical setting we would have a much greater frequency of a number of problems, such as arrhythmias and so forth, which create difficulties in blood pressure measurement. I think you have a problem and I do not know how it can be solved unless some of the manufacturers can develop devices which perform well on the 4th phase reading. Sir Horace Smirk: I have spent a lot of time listening with an electrical stethoscope and observing instrumental recording at the same time. I confirm the fmdings of Dr Hunyor that it is by no means infrequent for the Korotkoff sounds to be heard practically down to zero. Dr Stokes: It seems to me from what little I know about acoustics and the effect of age changes thereon, that perhaps those who think that they are measuring phase V are, as the years advance, probably measuring phase IV. Perhaps Dr labarthe would like to comment on this, and perhaps this would be an added plea for some consideration of the acoustic devices which place us outside the human aging factor. Dr Labarthe: I am not able to cite the age distribution

59

of our blood pressure observers, which might respond in part to your question, but I think the importance of the training device that Rose and Prineas (Lancet 1: 673, 1965) have developed is very clear. This involves, as I mentioned earlier, a casette recording which the trainee listens to with a head set. The basis of the training experience is to co-ordinate the timing, by a stopwatch, of a start signal at the beginning of the sequence of sounds and the point at which, respectively, systolic and diastolic pressures are reached. This can be done in fact with systolic and disappearance of sound only, or, with a special device they have developed, systolic plus 4th and 5th phase diastolic pressures. Now the requirement for proficiency which they recommend, and which we have employed in our programme, is that on a series of 12 subjects, the observer must reach agreement within plus or minus 1.0 seconds of the officially correct mean time interval for systolic and diastolic readings. One can apply a further requirement that the standard deviation must be within certain limits in some applications. I think this provides reasonable assurance of the auditory capacity of the observer. In fact we re-test all of our observers in this programme every six months. Therefore we have, within the practical limitations we must work under, periodic assessment of their auditory acuity. Prof. Lovell: Can you tell me when you have trained people as clearly and precisely as you have, whether they still show consistent between-observer variations? Do some despite training still tend to read high, compared with others who tend to read low? I ask this because we have used this same tape quite widely in Australia and in the Albury and Brunswick studies we had the same core of observers and we were all trained on the tapes. However, in both studies one particular observer tended to read high, another tended to read low, and the other two were in the middle. The studies were a year apart. Have you overcome that difficulty with, I am sure, much stricter training? Dr Labarthe: It is difficult to say. We know that at the time of training they jointly arrive at some nodal point in performance quality. It seems quite likely that as time goes on after training there is some diversion and one would expect performance to go back toward the pretraining stage. We will in fact be analysing our training data and our re-testing data in some detail in this regard within the next 3 to 4 months but we have not had the opportunity yet to look at this as extensively as we would have liked. It is a very important question. We know that there is some decrement in performance from the data we collect from day to day and week to week. We know that the observers tend to drift back toward digit preference habits of the kind that they had before. I would guess that this trend does exist; how serious it is and how well

Symposium on hypertension

60

we deal with it with periodical testing, I do not yet know. Prof. Wilcken: There is a difference between convenience and the truth and it is certainly understandable that for epidemiological studies one would want to use phase V. I really should know the answer to the question that I am asking, but I do not: If you measure the blood pressure directly and relate it to phase IV and phase V, to which does it relate best? Dr Labarthe: I would guess there are others here who are better qualified than I to respond. My impression, based on the few papers that deal directly with this problem and on the summary in Geddes' book (The Direct and Indirect Measurement of Blood Pressure, Year Book Medical Publishers, Oticago 1970), is that the intraarterial reading in diastolic pressure is likely to fall somewhere between the 4th and Sth phase; there may be wide individual differences in this. Prof. Lovell: I am delighted to hear you put it that way. Our own version would be that there are an equal

number of apparently very well made observations showing the best concordances with one as there are with the other. Dr R. Graham (Sydney): Could Dr Labarthe offer some explanation as to the mechanism of erroneous readings with smaller cuff sizes and suggest the best and optimal cuff size, considering the difference in length between patients. Dr Labarthe: Ordinarily it is arm circumference which is of concern and I think the important matter is that the circumference of the arm be properly taken into account when the cuff is applied. In our own programme, we have a set of successive sizes of cuffs; the currently manufactured cuffs from the Baum Company are marked on the inner surface so that the observer can determine quite readily whether the cuff of appropriate size is being used. Regarding cuff width and length of arm, I think this does not become a serious problem until one is dealing perhaps with paediatric populations.

Drugs 11 (Suppl. 1): 60-65

© ADIS Press 1976

Pre-Treatment Workup for Antihypertensive Treatment

G. Berglund Medical Department I, Sahlgren's Hospital, University of Goteborg, Goteborg

Summary

The prevalence of primary and secondary hypertension and of heart and kidney involve· ment was thoroughly studied in 689 hypertensive subjects derived from a blood pressure screening examination of a total population sample of Swedish men (n=7,452). The prevalence of secondary hypertension was found to be only 5%, the prevalence of surgically curable hypertension being even lower. Left ventricular hypertrophy and slight heart enlargement were each found in about one· third of the hypertensive patients, while severe heart enlargement, left ventricular hypertrophy on ECG, proteinuria, abnormal serum creatinine and urinary sediment were each found in about 5%. On the basis of these findings, a minimum pre-treatment workup in uncomplicated hypertension is proposed.