Comparison of direct and indirect arterial pressure measurements in hospitalized patients

Novel methods of testing and calibration of oscillometric blood pressure monitors

We present a robust method for testing and calibrating the performance of oscillometric non-invasive blood pressure (NIBP) monitors, using an industry standard NIBP simulator to determine the characteristic ratios used, and to explore differences between different devices. Assuming that classical auscultatory sphygmomanometry provides the best approximation to intra-arterial pressure, the results obtained from oscillometric measurements for a range of characteristic ratios are compared against a modified auscultatory method to determine an optimum characteristic ratio, Rs for systolic blood pressure (SBP), which was found to be 0.565. We demonstrate that whilst three Chinese manufactured NIBP monitors we tested used the conventional maximum amplitude algorithm (MAA) with characteristic ratios Rs = 0.4624±0.0303 (Mean±SD) and Rd = 0.6275±0.0222, another three devices manufactured in Germany and Japan either do not implement this standard protocol or used different characteristic ratios. Using a reference database of 304 records from 102 patients, containing both the Korotkoff sounds and the oscillometric waveforms, we showed that none of the devices tested used the optimal value of 0.565 for the characteristic ratio Rs, and as a result, three of the devices tested would underestimate systolic pressure by an average of 4.8mmHg, and three would overestimate the systolic pressure by an average of 6.2 mmHg.

Hypertension: empirical evidence and implications in 2014

High blood pressure (HBP) or hypertension (HTN) is one of the leading causes of cardiovascular (CV) morbidity and mortality throughout the world. Despite this fact, there is widespread agreement that the treatment of HBP, over the last half century, has been a great achievement. However, after the release of the new Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure-8 (JNC-8) guidelines, there have been heated debates with regard to what are the most evidence-based blood pressure goals. While JNC-8 claims that the goal blood pressure for otherwise healthy patients with mild hypertension (systolic blood pressure ≥140-159 mm Hg and diastolic blood pressure ≥90-99 mm Hg) should be <140/90 mm Hg; a recent Cochrane meta-analysis is in direct conflict with these recommendations. Indeed, a 2012 Cochrane meta-analysis indicated that there is no evidence that treating otherwise healthy mild hypertension patients with antihypertensive therapy will reduce CV events or mortality. Additionally, the Cochrane meta-analysis showed that antihypertensive therapy was associated with a significant increase in withdrawal due to adverse events. Thus, the current evidence in the literature does not support the goals set by the JNC-8 guidelines. In this review we discussed the strengths and limitations of both lines of evidence and why it takes an evidence-based medication to reduce CV events/mortality (eg, how a goal blood pressure is achieved is more important than getting to the goal). As medications inherently cause side effects and come at a cost to the patient, the practice of evidence-based medicine becomes exceedingly important. Although the majority of HTN studies claim great advantages by lowering HBP, this review finds severe conflicts in the findings among the various HTN studies, as well as serious epistemological, methodological and statistical problems that cast doubt to such claims.

Noninvasive studies of central aortic pressure

Our purpose is to review noninvasive methods for measuring central arterial pressure. Indices of central arterial pressure measured from central aortic and peripheral arterial waveforms have shown value in predicting cardiovascular events and death, as well as in guiding therapeutic management. This article reviews noninvasive techniques of measuring central arterial pressure that have been validated against intra-arterial pressure. This paper explains methods to derive central (aortic and carotid) pressure from radial and brachial sites. It focuses on specific issues of brachial calibration applied to carotid pressure waveforms, which were regarded as a surrogate of aortic pressures used in three major studies (Framingham, Asklepios, and Australian National Blood Pressure 2 studies). We explain why radial-based methods are superior to carotid-based methods for estimating central pressure. Physiological principles of pressure measurement need be satisfied to ensure accurate recording.

Influence of Cardiovascular Risk Factors on Total Arterial Compliance

BACKGROUND

Reduced total arterial compliance (TAC) may be a marker of preclinical vascular disease. Irreversible risk factors such as age and body habitus are determinants of TAC, the importance of which may have been hidden by reports in selected subgroups, such as the elderly and those with diabetes mellitus or hypertension. We sought the comparative influence of reversible and irreversible risk factors on TAC in a large primary prevention group.

MATERIALS AND METHODS

We studied 720 consecutive patients with and without cardiovascular risk factors but with no overt cardiovascular disease. TAC was calculated by the pulse-pressure method from simultaneous applanation tonometry and left ventricular outflow tract Doppler. Central pressure was derived using a transfer function from the radial tonometric waveform and calibrated using mean and diastolic brachial cuff pressure.

RESULTS

There were 192 patients with no cardiovascular risk factors, 180 patients with one cardiovascular risk factor, 173 patients with two cardiovascular risk factors, and 175 patients with three or more risk factors. Although age, gender, height, weight, hypertension, diabetes mellitus, hyperlipidemia, and number of risk factors were all significantly associated with TAC, age accounted for approximately 13% of the variance, and the only other independent predictors were height and weight. TAC was not significantly different in age-matched subgroups with single risk factors.

CONCLUSION

TAC is associated with multiple risk factors, but age is a major determinant. The influence of age and other correlates may dwarf the contribution of individual risk factors and therefore their alteration with therapy.

A new technique for assessing arterial pressure wave forms and central pressure with tissue Doppler

Background

Non-invasive assessment of arterial pressure wave forms using applanation tonometry of the radial or carotid arteries can be technically challenging and has not found wide clinical application. 2D imaging of the common carotid arteries is routinely used and we sought to determine whether arterial waveform measurements could be derived from tissue Doppler imaging (TDI) of the carotid artery.

Methods

We studied 91 subjects (52 men, age 52 ± 14 years) with and without cardiovascular disease. Tonometry was performed on the carotid artery simultaneously with pulsed wave Doppler of the LVOT and acquired digitally. Longitudinal 2D images of the common carotid artery with and without TDI were also acquired digitally and both TDI and tonometry were calibrated using mean and diastolic cuff pressure and analysed off line.

Results

Correlation between central pressure by TDI and tonometry was excellent for maximum pressure (r = 0.97, p < 0.0001). The mean differences between central pressures derived by TDI and tonometry were minimal (systolic 5.36 ± 5.5 mmHg; diastolic 1.2 ± 1.2 mmHg).

Conclusion

Imaging of the common carotid artery motion with tissue Doppler may permit acquisition of a waveform analogous to that from tonometry. This method may simplify estimation of central arterial pressure and calculation of total arterial compliance.

Recommendations for blood pressure measurement in humans and experimental animals: part 1: blood pressure measurement in humans: a statement for professionals from the Subcommittee of Professional and Public Education of the American Heart Association Council on High Blood Pressure Research

Accurate measurement of blood pressure is essential to classify individuals, to ascertain blood pressure-related risk, and to guide management. The auscultatory technique with a trained observer and mercury sphygmomanometer continues to be the method of choice for measurement in the office, using the first and fifth phases of the Korotkoff sounds, including in pregnant women. The use of mercury is declining, and alternatives are needed. Aneroid devices are suitable, but they require frequent calibration. Hybrid devices that use electronic transducers instead of mercury have promise. The oscillometric method can be used for office measurement, but only devices independently validated according to standard protocols should be used, and individual calibration is recommended. They have the advantage of being able to take multiple measurements. Proper training of observers, positioning of the patient, and selection of cuff size are all essential. It is increasingly recognized that office measurements correlate poorly with blood pressure measured in other settings, and that they can be supplemented by self-measured readings taken with validated devices at home. There is increasing evidence that home readings predict cardiovascular events and are particularly useful for monitoring the effects of treatment. Twenty-four-hour ambulatory monitoring gives a better prediction of risk than office measurements and is useful for diagnosing white-coat hypertension. There is increasing evidence that a failure of blood pressure to fall during the night may be associated with increased risk. In obese patients and children, the use of an appropriate cuff size is of paramount importance.

Pulse pressure vs. total arterial compliance as a marker of arterial health

BACKGROUND

Brachial pulse pressure (BPP) is a predictor of outcome in epidemiologic studies, but brachial and aortic pulse pressure (AoPP) may not correspond and both are influenced by multiple parameters including arterial properties and cardiac output. We sought to what extent pulse pressure (PP) measurements reflected direct measurement of arterial properties, assessed as total arterial compliance (TAC).

METHODS

We studied 123 patients (76 men; age 55 +/- 11); 31 normal controls, 46 patients with coronary artery disease and 46 patients with hypertension. PP was determined from brachial cuff pressure and TAC was measured by simultaneous radial applanation tonometry and pulsed wave Doppler of the LV outflow. AoPP was calculated using a transfer function from the radial waveform.

RESULTS

There was a significant difference between BPP and AoPP (57 +/- 16 vs. 45 +/- 14; P < 0.0001), although TAC correlated with BPP (r = -0.72; P = 0.01) and AoPP (r = -0.66; P = 0.01). In a multiple linear regression, the difference between BPP and AoPP was predicted by cardiac output (CO) (P = 0.002) and gender (P = 0.03). Bland-Altman analysis showed the best correspondence between BPP and AoPP in the middle tertile (CO 4.7 to 5.7 L min(-1)) with less correlation in the low and high tertiles. The same analysis by gender showed a higher difference in women than men (14 +/- 6 vs. 10 +/- 5; P < 0.0001). The difference between BPP and AoPP showed the best correlation in the control group and the worst in the hypertension group.

CONCLUSION

BPP correlates with TAC in men with normal cardiac function. However, in women, in patients at the low and high extremes of function, and in patients with preclinical and overt cardiovascular disease, there appears to be incremental value in measuring TAC.

Recommendations for Blood Pressure Measurement in Humans and Experimental Animals

Accurate measurement of blood pressure is essential to classify individuals, to ascertain blood pressure-related risk, and to guide management. The auscultatory technique with a trained observer and mercury sphygmomanometer continues to be the method of choice for measurement in the office, using the first and fifth phases of the Korotkoff sounds, including in pregnant women. The use of mercury is declining, and alternatives are needed. Aneroid devices are suitable, but they require frequent calibration. Hybrid devices that use electronic transducers instead of mercury have promise. The oscillometric method can be used for office measurement, but only devices independently validated according to standard protocols should be used, and individual calibration is recommended. They have the advantage of being able to take multiple measurements. Proper training of observers, positioning of the patient, and selection of cuff size are all essential. It is increasingly recognized that office measurements correlate poorly with blood pressure measured in other settings, and that they can be supplemented by self-measured readings taken with validated devices at home. There is increasing evidence that home readings predict cardiovascular events and are particularly useful for monitoring the effects of treatment. Twenty-four-hour ambulatory monitoring gives a better prediction of risk than office measurements and is useful for diagnosing white-coat hypertension. There is increasing evidence that a failure of blood pressure to fall during the night may be associated with increased risk. In obese patients and children, the use of an appropriate cuff size is of paramount importance.

Vital signs

BACKGROUND

Vital signs traditionally consist of blood pressure, temperature, pulse rate and respiratory rate, and are an important component of monitoring the patient's progress during hospitalisation. An initial search of the literature indicated that there was a vast volume of published information relating to this topic; however, there had been no previous attempt to systematically review this literature. This review was therefore initiated to identify, appraise and summarise the best available evidence relating to the measurement of vital signs in hospital patients.

OBJECTIVES

The objectives of this review were to present the best available information related to the monitoring of patient vital signs with regard to their purpose, limitations, optimal frequency of measurements, and what measures should constitute vital signs. The review also sought to identify additional issues of importance related to the individual parameters of temperature measurement, blood pressure assessment, pulse rate measurement and respiratory rate measurement.

REVIEW METHODS

This review considered all studies that related to the objectives and included neonatal, paediatric and/or adult hospital patients. The outcome measures of interest were those related to the accuracy of, required frequency of or the need for vital signs. The review also considered any study addressing some aspect of vital signs measurement to ensure all issues of importance were identified. The search sought to find both published and unpublished studies. Databases searched included CINAHL, Medline, Current Contents, Cochrane Library, Embase and Dissertation Abstracts. The references of all identified studies were examined for additional references. All studies were checked for methodological quality, and data was extracted using a data extraction tool.

RESULTS

Although a variety of measures may be useful additions to the traditional four vital sign parameters, only pulse oximetry and smoking status have been shown to change patient care and outcomes. There are suggestions that vital sign monitoring has become a routine procedure, but little useful information was identified in regard to the optimal frequency of vital sign measurement. It was noted that many of the important issues related to vital sign measurement have not been investigated through research.There is currently only limited research related to respiratory rate as a vital sign; however, its value as an indicator of serious illness has not been reliably established. There is only limited research relating to pulse rate measurements. Although routinely used for all hospital patients, the ability to detect serious physiological changes by assessment of pulse rate has not been rigorously evaluated. Many factors were identified that could potentially influence the accuracy of blood pressure measurement. Auscultation is accurate for the measurement of systolic blood pressure using phase I Korotkoff sound as the reference point, and for diastolic pressure if phase V Korotkoff sounds are used. Cuff size can influence accuracy, in that using a cuff that is too narrow will likely overestimate blood pressure and a cuff that is too wide will underestimate the pressure. Research suggests that blood pressure should be measured on the upper arm, while the arm is resting at approximate heart level. Studies have shown that healthcare workers often measure blood pressure in an incorrect and inaccurate way, and this is of some concern. However, a small number of studies suggest that education programs can be effective in improving blood pressure measurement techniques. The largest volume of research identified during this review related to the measurement of temperature. For accurate measurement of oral temperatures the thermometer should be positioned in either the left or right posterior sublingual pocket and remain in the mouth for 6-7 min. Although oxygen therapy and different types of breathing patterns will not influence accuracy of oral temperature measurements, hot or cold liquids will. For the measurement of tympanic temperatures, an ear tug should be used to help straighten the external auditory canal and so ensure measurement accuracy. The presence of impacted cerumen will likely result in inaccurate measurements. The only potential harm as a result of measuring vital signs was associated with glass mercury thermometers, in terms of rectal perforation, the risk of mercury poisoning was not clearly established.

CONCLUSIONS

Although there has been considerable research undertaken on many specific aspects of vital sign measurement, there is an urgent need for further primary research into the more general issues such as what parameters should be measured, the optimal frequency of measurements and the role of new technology in patient monitoring.

Vascular mechanics in the clinic

The bioengineer has more to contribute to medicine than he/she ever has in the past. The successful contribution must be based on such experiences as described by Donald McDonald in his collaboration with John Womersley. Clinician and engineer must come to know the other's problems, their weaknesses and their strengths. They must be prepared to compromise, but to know where compromise is warranted, and where it is not. The clinician must be prepared to change if he/she is to gain help from the engineer. Blind acceptance of old concepts (of "hypertension", and of cuff sphygmomanometric accuracy, etc.) needs enlightenment, while acceptance of physiological reality such as wave reflection needs emerge. The clinician's vocabulary will need to change. This chapter opens with a discussion of a time where knowledge of engineering, physics, physiology and medicine was meagre. These disciplines were small, but they did interconnect through the work of renaissance (and later) scientists. With increase in knowledge, the disciplines enlarged, and grew apart from each other. The challenge of today is to bring these closer together so that there may be some connection, some overlap, and so that the crevices between the disciplines are not so deep, and not such a deterrent to those who wish to engage in interdisciplinary activity.

Principles and techniques of blood pressure measurement

The gold standard for clinical blood pressure measurement continues to be readings taken by a physician using a mercury sphygmomanometer, but this is changing as mercury is gradually being phased out. The oscillometric technique, which primarily detects mean arterial pressure, is increasingly popular for use in electronic devices. Other methods include ultrasound (used mainly to detect systolic pressure) and the finger cuff method of Penaz, which can record beat-to-beat pressure noninvasively from the finger. The preferred location of measurement is the upper arm, but errors may occur because of changes in the position of the arm. Other technical sources of error include inappropriate cuff size and too rapid deflation of the cuff. Clinic readings may be unrepresentative of the patient's true blood pressure because of the white coat effect, which is defined as the difference between the clinic readings and the average daytime blood pressure. Patients with elevated clinic pressure and normal daytime pressure are said to have white coat hypertension. There are three commonly used methods for measuring blood pressure for clinical purposes: clinic readings, self-monitoring by the patient at home, and 24-hour ambulatory readings. Self-monitoring is growing rapidly in popularity and is generally carried out using electronic devices that work on the oscillometric technique. Although standard validation protocols exist, many devices on the market have not been tested for accuracy. Such devices can record blood pressure from the upper arm, wrist, or finger, but the arm is preferred. Twenty-four-hour ambulatory monitoring has been found to be the best predictor of cardiovascular risk in the individual patient and is the only technique that can describe the diurnal rhythm of blood pressure accurately. Ambulatory monitoring is mainly used for diagnosing hypertension, whereas self-monitoring is used for following the response to treatment. Different techniques of blood pressure measurement may be preferred in certain situations. In infants the ultrasound technique is best, whereas in pregnancy and after exercise the diastolic pressure may be hard to measure using the conventional auscultatory method. In obese subjects it is important to use a cuff of the correct size.

Factors affecting the validity of the standard blood pressure cuff

Fifty-eight patients, 31 women and 27 men, with a wide range of upper arm circumferences (20-43 cm), ages (16-82 years) and body mass indices (16-55 kg m-2) were studied. The direct blood pressure was measured in the brachial artery in one arm and simultaneously the indirect pressure was measured in the other arm using a large standard cuff (rubber bag 12 x 35 cm). The mean intra-arterial blood pressure was (systolic/diastolic) 137 +/- 25 mmHg (SD)/76 +/- 10 mmHg. With the cuff the mean blood pressure was 134 +/- 23 mmHg/85 +/- 11 mmHg. The cuff significantly underestimated the systolic blood pressure (3.2 +/- 11.4 mmHg, range -25-30 mmHg) while the diastolic pressure was overestimated significantly (8.8 +/- 8.5 mmHg, range -32-14 mmHg). The direct/indirect blood pressure difference correlated significantly to the intra-arterial systolic and diastolic pressures (systolic/diastolic; r = 0.44, P = 0.0006/r = 0.36, P = 0.0062), but only to the auscultatory diastolic pressure (r = -0.02, P = 0.9/r = -0.45, P = 0.0004). The direct/indirect difference correlated significantly to the arm circumference (r = -0.33, P = 0.01/r = -0.30, P = 0.02) as did the diastolic direct/indirect difference to pulse rate (r = 0.34, P = 0.009). Age did not correlate significantly to the direct/indirect blood pressure difference in this study (r = -0.02, P = 0.9/r = -0.10, P = 0.5). It can be concluded that in addition to the ratio between the arm circumference and the width of the cuff (rubber bag), there are other sources of systematic errors of indirect blood pressure measurement, in particular pulse rate and the level of indirect blood pressure. If corrections could be made with regard to these variables, it is obvious that the reliability of the indirect method, especially when used in epidemiological contexts, would increase.

Evaluation of self-measured home vs. clinic intra-arterial blood pressure

Home blood pressure (BP) monitoring is useful in the clinical management of patients with hypertension and the identification of those with "white-coat" hypertension; i.e. high readings in the clinic but normal BP at home. In the process of evaluating this technique, we compared self-measured home BP with intra-arterial BP. Healthy white men (n = 40) of 20-40 years of age and body weight below 95 kg were recruited by advertising in the local newspaper. Following a standardized procedure, performed within 2-4 weeks of a response to the advertisement, BP was measured by a physician at a clinic screening, by the subject at home (14 readings in 7 days) and finally in the clinic concomitantly intra-arterially and oscillometrically. The correlation coefficient for mean (M) home BP (r = 0.73) and oscillometric BP (r = 0.74) against intra-arterial BP were slightly higher than for screening BP (r = 0.65). However, in plots of the differences for individual MBP between the methods against the average of the methods, it appears that at levels of average MBP above 100 mmHg, screening BP overestimates the BP level, while this was not the case for home BP or oscillometric BP. Thus, by using intra-arterial measurement as standard of comparison, subject self-measured home BP is a reliable method of estimating blood pressure level in young men. Home BP measured shortly after screening and recruitment provides useful information of resting BP in subjects who potentially may have initial anxiety about BP measurement.

Pseudohypertension and the measurement of blood pressure

Riva-Rocci Korotkoff (RRK) blood pressure measurements may overestimate the intra-arterial pressure (IAP) in individual patients. To study pseudohypertension, defined as an overestimation larger than 10 mm Hg, we compared RRK and IAP measurements in 76 patients. These patients were considered to be at risk for pseudohypertension because of high age, hypertension, or vascular disease. RRK measurements underestimated simultaneously measured systolic IAP values by 6.0 +/- 6.5 (mean +/- SD) mm Hg, whereas simultaneous diastolic RRK readings overestimated the IAP by 1.9 +/- 5.6 mm Hg. Diastolic overestimation increased slightly with age. Vascular rigidity, as measured by counterpressure plethysmography, did not correlate with these errors. Systolic and diastolic pseudohypertension was observed in two and five patients, respectively. Pseudohypertension was only present in the group in which IAP was measured in the aorta. However, the number of patients with systolic and diastolic pseudohypertension could be increased to three and seven by using the average intra-arterial systolic and diastolic pressure during an RRK measurement or to six and 11 by using the IAP during a control period just before an RRK measurement rather than the IAP at the moment of appearance or disappearance of the Korotkoff sounds. The widely diverging prevalence of pseudohypertension described in the literature might be explained because of such different comparison techniques.

Epidemiology of hypertension during pregnancy

Hypertension during pregnancy, defined as a diastolic blood pressure of at least 90 mm Hg, occurs in about 7% of Western countries. Primiparity and familial factors are the most important risk factors. Fifty percent of women experienced blood pressure elevation as late as the last month of pregnancy.

Noninvasive determination of the left ventricular end-systolic pressure

To find a noninvasive method for estimating left ventricular end-systolic pressure, 40 patients were studied during cardiac catheterization. Arterial pressure was taken directly from the ascending aorta. Carotid pulse tracing and measurement of blood pressure by cuff sphygmomanometry were taken simultaneously. The tracings were calibrated and left ventricular end-systolic pressure was estimated directly and indirectly. Simple linear regression analysis gave the equations: (1) left ventricular end-systolic pressure direct = 0.56 left ventricular end-systolic pressure indirect + 43.8 (r = 0.61, P = 0.00004), and (2) left ventricular end-systolic pressure direct = 0.39 systolic arterial pressure indirect + 48.8 (r = 0.62, P = 0.00002). To test the accuracy of the technique the study was continued in 40 patients. Left ventricular end-systolic pressure was also estimated by the 2 equations. Left ventricular end-systolic pressure direct was correlated with left ventricular end-systolic pressure estimated by the 2 equations and there was no statistical difference. This noninvasive technique is a bedside method for clinical measurement of left ventricular end-systolic pressure.

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 Korotkoff sound

As the auscultatory method of blood pressure measurement relies fundamentally on the generation of the Korotkoff sound, identification of the responsible mechanisms has been of interest ever since the introduction of the method, around the turn of the century. In this article, a theory is proposed that identifies the cause of sound generation with the nonlinear properties of the pressure-flow relationship in, and of the volume compliance of the collapsible segment of brachial artery under the cuff. The rising portion of a normal incoming brachial pressure pulse is distorted due to these characteristics, and energy contained in the normal pulse is shifted to the audible range. The pressure transient produced is transmitted to the skin surface and stethoscope through deflection of the arterial wall. A mathematical model is formulated to represent the structures involved and to compute the Korotkoff sound. The model is able to predict quantitatively a range of features of the Korotkoff sound reported in the literature. Several earlier theories are summarized and evaluated.

Magnitude and mechanisms of the antihypertensive action of labetalol, including ambulatory assessment

The blood pressure (BP) effect and modes of action of a twice daily regimen of labetalol (mean 450 mg/day) were assessed in ten mild to moderate hypertensives using continuous ambulatory BP monitoring. The reflex control of BP during physiological interventions was examined just prior to the next dose of medication to estimate the residual alpha- and beta-adrenoceptor blockade. Global 24 h BP was reduced by 15/9 mm Hg, and home pressures by 13/11 mm Hg. The predominant antihypertensive effect was noted during the waking hours. During dynamic exercise significant inhibition of the heart rate and blood pressure rise occurred. Coupled with a reduction of the post-release BP 'overshoot' in Valsalva's manoeuvre, the response resembles that seen with beta-adrenoceptor blockade. A small alpha-adrenoceptor blocking action was evident in one patient's response to the Valsalva manoeuvre.

Accuracy and reliability of two indirect ambulatory blood pressure recorders: Remler M2000 and Cardiodyne Sphygmolog

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Anti-hypertensive action of labetalol: a detailed profile

Continuous, ambulatory blood pressure (BP) and self measured home recordings were used to study the response of ten mild to moderate hypertensives taking a twice daily labetalol dosage. Testing of cardiovascular reflexes was carried out 12 hours after a dose of drug. The mean 24 hour BP was reduced from 145/80 +/- 14/7 (SD) mmHg to 130/71 +/- 11/6 (p less than 0.001) and home BP from 147/96 +/- 15/9 to 134/84 +/- 10/9 (p less than 0.01). The predominant effect of labetalol was evident during the waking hours. A residual 9.5% BP reduction was seen 12 hours after a dose compared to an 11% lowering effect over the entire 24 hours (NS). No symptomatic hypotensive episodes were noted. Significant inhibition of heart rate and BP rise during dynamic exercise (p less than 0.01) and reduction of post-release BP "overshoot" (p less than 0.01) in Valsalva's manoeuvre indicated a beta adrenoceptor blocking effect. There was however a reduction in the rate of rise of BP during static handgrip (p less than 0.01) indicating a small alpha adrenoceptor blocking component. This study has demonstrated the efficacy of a twice daily regimen of labetalol in continuously lowering BP. The mode of action of the drug during exercise (static and dynamic) and Valsalva's manoeuvre would indicate a predominant beta adrenoceptor blocking action.

Error in blood-pressure measurement due to incorrect cuff size in obese patients

Trained nurse-specialists obtained 84 000 blood-pressure measurements in 1240 obese subjects using cuffs of the three standard adult sizes in a randomised order. The differences in readings between the three cuffs were smallest in non-obese subjects and became progressively greater with increasing arm circumference (AC) in the obese population. The regular cuff (12 X 23 cm) showed the greatest bias in relation to AC. Formulae and a table have been derived to correct the measurement error caused by cuffs of inappropriate size at various ACs. The reported high prevalence of hypertension in obese subjects may be greatly overestimated.

Orthostatic hypotension after the first administration of prazosin in hypertensive patients: role of the plasma volume

1. Prazosin (2 mg, p.o.) was administered to nine patients with essential hypertension while intra-arterial pressure was recorded by an Oxford portable apparatus. In all patients, 30 min-3 h after the administration, systolic and diastolic pressure fell on assuming the upright posture and four patients fainted. No correlation was found between the degree of fall in pressure and the plasma concentration of the drug. Acute expansion of the plasma volume by means of 6% Dextran infusion reduced the orthostatic blood pressure fall in all cases and a significant inverse correlation was found between plasma volume and orthostatic fall of pressure. 2. After ten days of continuous treatment with prazosin, 2 mg daily, a significant decrease in blood pressure was observed while orthostatic hypotension disappeared, probably due to the plasma volume expansion induced by the drug.

The methodology of blood pressure recording

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Comparison of intra-arterial and indirect blood pressures at rest and during isometric exercise in hypertensive patients before and after metoprolol

1. Blood pressure was measured both directly and indirectly in seven hypertensive patients before and after a single oral dose of 100 mg metoprolol, at rest and during sustained handgrip. 2. Intra-arterially measured systolic and diastolic blood pressure increased linearly with time during sustained handgrip at 50% of maximal voluntary contraction. This linearity persisted for 60 s or more in most cases. Heart rate increased linearly for the first 30 s. 3. Indirectly measured blood pressure using an observer bias minimizing Auto-Manometer, under-read systolic and over-read diastolic pressure both at rest and during handgrip. 4. By exact timing of recorded values during handgrip and linear extrapolation (or interpolation) from base-line readings, mean values at 30 and 60 s of handgrip were calculated. The relationship between direct and indirect values remained the same at base-line and 30 s of handgrip. At 60 s of handgrip, this was true only for diastolic pressure. For systolic pressure, indirect and direct values almost coincided. 5. After metoprolol, directly recorded pressure fell slightly (7--12 mm Hg, 0.02 less than P less than 0.10), both at rest and during handgrip, and heart rate fell by 15--18 beats/min (P less than 0.01). The systolic blood pressure and heart rate effect of metoprolol at 1 min handgrip correlated with peak plasma drug levels. Indirectly measured blood pressure did not change significantly. 6. The rate of rise in heart rate and blood pressure from base-line to 60 s handgrip was not significantly influenced by metoprolol.

Comparison of performance of various sphygmomanometers with intra-arterial blood-pressure readings

Seven types of sphygmomanometer were used in random order on each of nine hypertensive patients and the readings compared with simultaneous intra-arterial blood-pressure recordings. All the devices gave significantly different values for systolic pressure, and only two measured diastolic pressure without significant error. Systolic pressure was consistently underestimated (range 31-7 mm Hg), and all but one instrument overestimated diastolic pressure (range 10-2 mm Hg). The variability of readings was least with the standard mercury sphygmomanometer and the random-zero machine, while with some of the more automated devices single readings were in error up to -68/33 mm Hg. The strong correlations found between intra-arterial and cuff systolic pressures with all devices tested and significant correlations for diastolic pressure with all but one device indicate that, with one possible exception, the sphygmomanometers would give accurate results where a change in blood pressure was the main concern.

The infrasound blood-pressure recorder. A clinical evaluation

Comparisons with direct recordings show that the Physiometrics automatic blood-pressure recorder does not accurately reflect intra-arterial pressure and tends to over-read both systolic and diastolic pressures.