Sons de Korotkoff: desenvolvimento da pesquisa em esfigmomanometria na Escola de Enfermagem da USP

Este artigo tem como objetivos reverenciar Sergei Nicolai Korotkoff por ocasião do centenário da descoberta do método auscultatório de medida da pressão arterial na Rússia, em 1905; relatar os fatos que culminaram no desenvolvimento da esfigmomanometria no Brasil; historiar a valiosa contribuição da Escola de Enfermagem da Universidade de São Paulo (EEUSP) no desenvolvimento da pesquisa, na área da medida da pressão e analisar o produto da linha de pesquisa "Influência da Largura do Manguito na Medida da Pressão Arterial", gerada na EEUSP a partir de 1974. O artigo relata a consolidação dos achados iniciais pelos estudos que permitiram a formação dos primeiros doutores na área, que sugere a confirmação de hipóteses em estudos longitudinais.

Direct and indirect blood pressure in normotensive and hypertensive subjects

OBJECTIVES

To compare intrabrachial blood pressure (I-BP) with simultaneously measured contralateral auscultatory (A-)BP in hypertensive and normotensive subjects. The question was whether differences between direct and indirect BP are influenced by the BP levels.

SUBJECTS

Hypertensive subjects treated with either placebo (n = 10) or metoprolol (n = 8) and age-matched normotensive subjects (n = 15), selected from a defined patient population waiting for cholecystectomy or hernia repair. Measurements were performed pre-induction of anaesthesia.

RESULTS

In the hypertensive subjects, cuff systolic BP (SBP) was lower than I-BP by an average of 8 mmHg (placebo-) and 7 mmHg (metoprolol-treated), whereas diastolic A-BP (A-DBP) was 3 and 7 mmHg higher, respectively. In the normotensive subjects, mean A-SBP and I-SBP agreed closely, whereas A-DBP was 11 mmHg higher. Thus, SBP differences (i.e. indirect-direct BP) were significantly less and DBP differences significantly greater in the normotensive than in the hypertensive subjects (P < 0.05). Plasma renin activity and adrenalin showed better correlations with A-MBP than with I-MBP.

CONCLUSIONS

The drift of cuff systolic readings fell progressively below the intrabrachial values when BP increased, whilst diastolic cuff values approached the direct pressures. Since A-MBP did not significantly differ from I-MBP in any group, one must ask whether hypertension would be more correctly defined according to MBP criteria.

Automated blood pressure determination during exercise test. Clinical evaluation of a new automated device

The accuracy and reproducibility of a new automatic device (P) specially designed for noninvasive blood pressure monitoring during the exercise stress test were evaluated in 50 consecutive subjects (34 normotensives and 16 hypertensives). Automatic measurements were compared with those taken by a sphygmomanometer (RR). A good agreement between systolic pressure values obtained by the two methods was found (RR 159 +/- 30 mmHg, P 158 +/- 28 mmHg, mean difference = -1.53 +/- 13 mmHg, p = 0.166, ns). On the contrary the new device significantly underestimated diastolic pressure values (RR 89.3 +/- 13 mmHg; P 84 +/- 13 mmHg, mean difference -5.37 +/- 9.3, p < 0.001). In conclusion the new device seems able to measure systolic but underestimates diastolic blood pressure both in hypertensives and in normotensives during the effort test.

[The indirect measurement of arterial pressure as a function of cuff width in patients in the immediate preoperative phase, the phase of entry into the operating room and in the postanesthesia phase]

The goal of this study was to compare blood pressure measures using two sizes of cuffs: one standard width (12 cm) and other with correct width that is 0.38 of arm circumference as recommended by American Heart Association. The comparisons were done among surgical patients in mediate perioperative phase, reception area of operation room and postoperative phase during the staying of the patient in the recovery room. The results demonstrated that the arterial blood pressure was hypoestimated by the use of the standard width cuff, reaching values up 30 mmHg in the systolic arterial pressure and 30 mmHg in the diastolic ones.

Measurement of blood pressure in the obese

There is a need for caution in measuring blood pressure in the obese. Problems related to adequate cuff-bladder size and shape are apparent from a review of the literature. Imperfections in experiments comparing intra-arterial/indirect blood pressure measurements remain. Cuff characteristics, as well as cuff-bladder width and length, can bias measurement of blood pressure in the obese. Authoritative committee recommendations and the differing needs of blood pressure measurement in obese adults and children still need to be rationalized. Manufacturing faults of cuff bladder and cuff availability continue to be a problem for blood pressure measurement in the obese. Measurement of blood pressure in large obese and large muscular arms may require different adjustments for cuff width and arm circumference. Nomograms for adjusting blood pressure recording in the obese are inadequate. The most important adjustment for measuring blood pressure in the obese derives from choosing the correct cuff width-arm circumference (CW/AC) ratio. Such action reduces the intersubject variability of blood pressure measurement in clinical and epidemiologic studies. Past studies probably overestimated blood pressure level in the obese and so underestimated the risk of elevated blood pressure in the obese.

Accuracy of four indirect methods of blood pressure measurement, with hemodynamic correlations

In 38 adults undergoing cardiac surgery, 4 indirect blood pressure techniques were compared with brachial arterial blood pressure at predetermined intervals before and after cardiopulmonary bypass. Indirect blood pressure measurement techniques included automated oscillometry, manual auscultation, visual onset of oscillation (flicker) and return-to-flow methods. Hemodynamic measurements or calculations included heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect and intraarterial blood pressure values were compared by simple linear regression by patient and measurement period. Measurement errors (arterial minus indirect blood pressure) were calculated, and stepwise regression assessed the relationship between measurement error and heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect to intraarterial blood pressure correlation coefficients varied over time, with the strongest correlations often occurring at the first and last measurement periods (preinduction and 60 minutes after cardiopulmonary bypass), particularly for systolic blood pressure. Within-patient correlations between indirect and arterial blood pressure varied widely--they were consistently high or low in some patients. In other patients, correlations were especially weak with a particular indirect blood pressure method for systolic, mean, or diastolic blood pressure; in some cases indirect blood pressure was inadequate for clinical diagnosis of acute blood pressure changes or trends. The mean correlations between indirect and direct blood pressure values were, for systolic blood pressure: 0.69 for oscillometry, 0.77 for auscultation, 0.73 for flicker, and 0.74 for return-to-flow; for mean blood pressure: 0.70 for oscillometry and 0.73 for auscultation; and for diastolic blood pressure: 0.73 for oscillometry and 0.69 for auscultation. The mean measurement errors (arterial minus indirect values) for the individual indirect blood pressure methods were, for systolic: 0 mm Hg for oscillometry, 9 mm Hg for auscultation, -5 mm Hg for flicker, 7 mm Hg for return-to-flow; for mean: -6 mm Hg for oscillometry, and -3 mm Hg for auscultation; and for diastolic: -9 mm Hg for oscillometry and -8 mm Hg for auscultation. Mean measurement error for systolic blood pressure was thus least with automated oscillometry and greatest with manual auscultation, while standard deviations ranging from 9 to 15 mm Hg confirmed the highly variable nature of single indirect blood pressure measurements. Except for oscillometric diastolic blood pressure, a combination of systemic hemodynamics (heart rate, stroke volume index, systemic vascular resistance index, and cardiac index) correlated with each indirect blood pressure measurement error, which suggests that particular numeric ranges of these variables minimize measurement error.(ABSTRACT TRUNCATED AT 400 WORDS)

Ratio of cuff width/arm circumference as a determinant of arterial blood pressure measurements in adults

Recommendations state that the optimum ratio of blood pressure cuff width/arm circumference (CW/AC) is about 0.4. In this study of middle-aged men (n = 940) and women (n = 1484), we analysed the effect of CW/AC on blood pressure measurement variability and its interaction with age, body mass index (BMI), pulse rate and room temperature. In univariate polynomial regression, the variability (R2) in blood pressure that was explained by CW/AC was greater for women (systolic 6.3% and diastolic 5.7%) than for men (2.0% and 0.5%). In multivariate analysis the maximum variability explained independently by CW/AC was 2.7% for male and 6.7% for female systolic blood pressure, and 1.1% and 6.0% for male and female diastolic blood pressure, respectively. For systolic blood pressure this represented 10.4% of the explained variability in men and 9.3% of that in women. CW/AC is an important independent contributor to inter-individual variation in blood pressure measurement. It should therefore be taken into consideration in epidemiological studies and when medical care is being planned.

[The indirect measurement of arterial pressure: a review]

This study deals with the indirect arterial blood pressure measurement, particularly the American Heart Association recommendations for sphygmomanometry References are made regarding the ratio arm circumference/cuff width and the errors caused by inadequate cuff size. Several variables involved in the procedure of arterial blood pressure measurement are discussed.

Point of view: why hypertension is overdiagnosed and overtreated in 1987

1. The decision whether arterial blood pressure (BP) is elevated or normal is usually based on inadequate data: few readings in the presence of great variability of BP; levels higher in the presence of the doctor; and diastolic BP often higher sitting and standing than lying. 2. Assessments of response and of the need for increases in drug dosage are also based on insufficient data. 3. Increased morbidity and mortality from stroke and heart attack, and incomplete correction with treatment have been interpreted as suggesting further benefit from aggressive reduction of BP to 'normal' in all patients. 4. The emergence of powerful drugs with few side-effects, and the promise of lowering office BP to 'normal' as monotherapy, has removed the hesitation to treat 'mild' hypertension. 5. Attempts to lower sitting office diastolic BP to 'normal' have led to increasing drug dosage, dose-related, drug-specific side-effects, and lethargy due to hypotension. 6. Newer self-measurement BP units can be used easily by most patients, cost less than five visits to the doctor and provide a cheap method of obtaining sufficient data on which to base informed management decisions. Supported by normal echocardiographic left ventricular mass, normal 'home BP' (including lying diastolic) permits many mild hypertensives to remain off medications. 7. Non-drug therapy avoids or reduces long-term drug therapy, with its side-effects.

A comparative study of the measurement of mean arterial blood pressure using automatic oscillometers, arterial cannulation and auscultation

Mean brachial artery pressures determined by five different non-invasive automatic oscillometric and one auscultatory preferred (oscillometric back-up) blood pressure (BP) monitors were compared with mean arterial pressures (MAP) obtained by cannulation of the radial artery of the same arm. The devices tested all performed similarly, showing a wide range of variation (+40% to -29%) compared with the directly measured MAP, and all tended to over-read at low values and under-read at high values. Trend information was generally acceptable, but occasionally was misleading. In addition, using one of the devices, systolic and diastolic blood pressure measurements were compared with those obtained by auscultation. This gives a range of differences from +22 to -25 mmHg for systolic and +20 to -12 mmHg for diastolic BP measurements. (The average fell within 1.0 mmHg of the auscultatory measurement, with a standard deviation of 10 mmHg.) Thus, the automatic oscillometric BP monitors tested were comparable in accuracy to auscultatory BP measurement, and are satisfactory for routine use in the appropriate clinical context. However, in settings where significance is to be attached to individual BP readings rather than to trends, or where a high degree of accuracy is required, automatic oscillometric machines cannot be regarded as satisfactory alternatives to arterial cannulation.

Clinical comparison of automated auscultatory and oscillometric and catheter-transducer measurements of arterial pressure

Arterial pressure measurements recorded from a radial artery catheter-transducer (RAC) system were compared with similar data obtained from an automated sphygmomanometer that uses both oscillometric (OSC) and auscultatory measurement techniques. Data were obtained from 50 patients during and immediately after surgery. The fundamental frequency of the RAC system was 23.7 +/- 6.7 Hz (mean +/- SD; range, 13 to 40 Hz), and the damping coefficient was 0.26 +/- 0.06 (mean +/- SD; range, 0.15 to 0.34). Linear regression analysis of RAC against OSC values (n = 385) revealed the following correlations: (1) systolic pressure: OSC = 0.92(RAC) + 3.5, r = 0.91; (2) diastolic pressure: OSC = 0.92(RAC) + 1.3, r = 0.76; and (3) mean pressure: OSC = 0.96(RAC) + 0.68, r = 0.84. There were significant differences between each pair of pressure values; mean percent differences (RAC pressure minus OSC pressure) were 4.5 +/- 0.3%, 5.5 +/- 0.7%, and - 2.7 +/- 0.5% for systolic, diastolic, and mean values, respectively. Manual and automated auscultatory measurements closely agreed, and both correlated well with OSC values for systolic and diastolic pressure. However, both manual and automated auscultatory, as well as OSC measurements, underestimated RAC systolic and overestimated RAC diastolic pressure.

Comparative accuracy of two new electronic devices for the noninvasive determination of blood pressure

Recent developments in behavioral approaches to cardiovascular disease have called for physiological monitoring devices that reduce experimenter bias, are easy to operate, can be used ambulatorily, and/or provide ongoing, automated monitoring of pertinent cardiovascular functions--i.e., blood pressure and heart rate. Neither the invasive monitoring (via catheterization) nor the standard auscultatory method of blood pressure determination, however, has these characteristics. In the present study, two new methods/devices--(1) a low-weight, low-cost, battery-operated sphygmomanometer (SM), and (2) a more expensive automated electronic SM with electrical pump-are compared with each other and with the more common auscultatory method and a standard mercury SM. Both new devices were also compared with a standard pulse count. Data were derived from 10 readings of 10 healthy subjects each across the three possible comparisons, thus totaling N = 30. Correlation coefficients and average differences were computed and indicated high intercorrelations (between r = .89 and r = .99) between each pairing of the new electronic devices and the mercury SM. Intercorrelations of blood pressure determination with the two new electronic devices, however, were only moderate. Potential reasons for the variability are discussed, and guidelines for the optimal use of the new, easy-to-operate electronic devices are presented.

Noninvasive estimation of central aortic pressure using the oscillometric method for analyzing systemic artery pulsatile blood flow: comparative study of indirect systolic, diastolic, and mean brachial artery pressure with simultaneous direct ascending aortic pressure measurements

Brachial artery pressures determined by the oscillometric method were compared with simultaneous central aortic (Ao) pressure measurements in 30 patients undergoing cardiac catheterization. Three simultaneous oscillometric and central Ao pressure readings were obtained in each patient. Central Ao pressures ranged widely for systolic (SP) (98 to 177 mm Hg), diastolic (DP) (41 to 97 mm Hg), and mean (MP) (60 to 120 mm Hg) pressure values. The mean percent errors (pressure difference divided by central Ao pressure) and "within subject" standard deviation were 1% and 3% for SP, 2% and 4% for DP, and -3% and 7% for MP. The percent error in oscillometric SP and DP estimates was not significantly influenced by cardiac index, systemic vascular resistance, heart rate, body surface area, or left ventricular ejection fraction. The oscillometric method provides accurate, reproducible, and convenient estimates of central Ao SP and DP and may be particularly useful when indirect blood pressure measurements are required for the noninvasive assessment of left ventricular function in patients without aortic stenosis.

An evaluation of blood pressure measurement

The accuracy of routine measurements by nursing staff of systemic arterial, central venous, pulmonary artery and pulmonary capillary wedge pressures was determined. There was a significant difference between direct mean arterial blood pressure measurements and routine indirect measurements by the nursing staff in the pressure range of 50--100 mmHg, whereas there was no significant difference between direct and indirect measurements when indirect measurements were made by specially trained hypertension clinic personnel. However, there was a good correlation between direct and indirect measurements in each instance, indicating that changes in blood pressure could be adequately followed by both groups. Systems commonly used to measure blood pressure directly were tested. Limits in frequency response preclude the routine direct measurement of systolic or diastolic blood pressures. If direct systolic and diastolic pressure measurements are required, it is necessary to check the performance of the amplifier and recording system, attach the transducer to the patient, and determine and adjust, if necessary, the natural frequency and damping coefficient of each system before each measurement. However, it is suggested that a knowledge of systolic and diastolic pressure measurements seldom improves patient management, and if mean pressures are accepted, reliable routine measurements may be obtained by the nursing staff. The digital display of the systems tested may be accepted for mean arterial pressure, but for accurate mean central venous and pulmonary capillary wedge pressure measurements, it is necessary to interpret the trace on a chart recorder; pulmonary artery pressure can often only be estimated.

Dynamic reactions produced by deflating a blood pressure cuff

Intra-arterial pressure was recorded at various points in the compressed segment of brachial artery during deflation of a standard blood pressure cuff in human subjects with arms of normal girth. Cuff pressure and the Korotkoff sounds also were recorded simultaneously. The data were analyzed in terms of the various dynamic reactions produced by cuff deflation, which may influence the auscultatory indications of systolic and diastolic blood pressure. Cuff pressure was incompletely transmitted to the compressed arterial segment. As a result, muffling, the auscultatory indication of diastolic pressure, occurred at a cuff pressure higher than the directly recorded intra-arterial diastolic blood pressure. The first Korotkoff sound, on the other hand, provided a close approximation of intra-arterial systolic pressure. This may be due to a delay in penetration of the diminutive pulse waves into the distal part of the compressed arterial segment at systolic levels of cuff pressure. This effect appears to compensate for other influences tending to raise the indirect reading of systolic blood pressure. The extent of the delay in penetration should be dependent on the length of the collapsed segment, which in turn is a function of cuff width.