What are the normal levels for ambulatory blood pressure measurement?

With acceptance of ambulatory blood pressure measurement as a useful technique in the management of hypertension, the question of what constitutes the upper limit of normality for 24 h blood pressures has been the subject of a number of reviews [1,2]. In fact, there has been remarkable similarity in a number of large population studies [3-10]. For example, taking the 95th percentile as the upper limit of the distribution of daytime blood pressure in various studies in different countries (Internation Database 141/88 mmHg [3,4], Ireland 138/89 mmHg [5], Belgium 137/88 mmHg [6], Japan 138/83 mmHg [7], Denmark 139/88 mmHg [8] and Italy 134/88 mmHg [9,10] gave variations of less than 7/6 mmHg for systolic and diastolic blood pressures, respectively, the average for all studies being 138/87 mmHg (for review, [6]). A review of the literature carried out independently by the American Society of Hypertension [11] and our group [1,2,6] produced an identical recommendation for the levels of daytime blood pressure that may be regarded as normal and abnormal, namely, that blood pressures above 140/90 mmHg are probably abnormal and that blood pressures below 135/85 mmHg are probably normal. Moreover, the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure in its recent communication takes blood pressures of awake subjects below 135/85 mmHg to be normal [12].

Conventional and ambulatory measurements of blood pressure in old patients with isolated systolic hypertension: baseline observations in the Syst-Eur trial.

OBJECTIVES: To compare clinic and am measurements of blood pressure in old patients with isolated systolic hypertension and their reproducibilities. PATIENTS: In total 610 patients aged >/= 60 years with isolated systolic hypertension detected by clinic measurement were monitored during the placebo run-in phase of the Syst-Eur trial. METHODS: The time-weighted 24 h blood pressure, clock-time day and night blood pressures, the cumulative-sum-derived crest and trough blood pressures and the high and low blood pressure levels according to the square-wave model were computed. The daily alteration between the high and low spans of blood pressure was quantified using the day-night difference, the cumulative-sum-derived magnitude of circadian alteration, the Fourier amplitude and the difference between the high and low blood pressure levels of the square-wave model. RESULTS: The daytime am systolic blood pressure was, on average, 21 mmHg lower than the clinic systolic blood pressure, whereas diastolic pressure was, on average, similar with both techniques of measurement. Clinic levels of blood pressure in the 141 patients who underwent repeat measurements and the parameters describing the difference between the daily high and low spans of blood pressure were equally reproducible. However, both were less reproducible than the ambulatory blood pressure levels. The reproducibility coefficients, expressed as percentages of near maximum variation, were 49 and 50% for the clinic systolic and diastolic blood pressures, 30 and 32% for the mean 24 h systolic and diastolic blood pressures and 45-55% for the parameters describing the daily alteration between the high and low spans of blood pressure. CONCLUSION: Values of blood pressure in old patients with isolated systolic hypertension were more reproducible for ambulatory than they were for clinic measurements. Levels in patients selected because they have a high clinic blood pressure may be substantially higher with conventional than they are with daytime ambulatory measurement. The prognostic significance of this difference for the present patients is currently under investigation.

Epidemiology of ambulatory blood pressure monitoring.

An operational threshold for making clinical decisions on the basis of ambulatory blood pressure monitoring must be defined [1-3]. This requires that the relationship between the ambulatory blood pressure and the incidence of cardiovascular complications be clarified beyond present understanding [4-7]. In addition, the distribution of the ambulatory blood pressure must be characterized better under various conditions and for various populations and compared with the centrality and spread of the conventional blood pressure under similar circumstances.

Predictive value of clinic blood pressure variability for pressure changes during placebo in elderly hypertensives.

OBJECTIVES: Syst-China is the ongoing placebo-controlled double-blind outcome trial in older (aged 60 years or more) Chinese patients with isolated systolic hypertension (systolic blood pressure 160-219 mmHg and diastolic blood pressure < 95 mmHg). This article is based on the data accumulated until 31 August 1992. Its purpose is to investigate the extent to which the variability in the clinic blood pressure readings at baseline could predict the blood pressure changes observed in the placebo arm of the trial. METHODS: From 2379 patients recruited into the trial, 728 [455 men and 273 women, aged 66.7+/-5.5 years (mean +/- SD)] were selected, because their blood pressure readings for the three run-in visits as well as 3, 6 and 12 months after random allocation were available. Overall and between-visit blood pressure variabilities at baseline were estimated from the two readings obtained with the subject seated during the first and second run-in visits. The baseline blood pressure used to calculate the blood pressure changes during follow-up was the average of the two readings during the third run-in visit. RESULTS: The blood pressure variability at baseline was larger for women than it was for men. For all of the subjects combined, the blood pressure had decreased by 4.1+/-14.4 mmHg (P < 0.001) systolic and 0.5+/-6.7 mmHg (P < 0.06) diastolic by the 3-month follow-up visit, by 8.5+/- 15.2 and 1.4+/-7.5 mmHg, respectively, after 6 months and by 10.3+/-15.7 and 1.9+/-7.9 mmHg, respectively, after 1 year (p < 0.001 for all). Stepwise multiple regression analysis showed that sex, age, alcohol intake and the blood pressure at baseline were significant determinants of the long-term (1 year) blood pressure changes. Aftger adjustment for the aforementioned covariates, the between-visit variability was a significant predictor of the changes in the diastolic blood pressure after 1 year of placebo treatment for the men (partial r+/-SEM -0.36+/-0.12, P < 0.01) and for all of the subjects (-0.19+/-0.09, P < 0.05). For men, the partial regression coefficient between the overall variability and the changes in the diastolic blood pressure also attained statistical significance (-0.39+/- 0.14, P < 0.01). CONCLUSION: For older Chinese patients with isolated systolic hypertension, in particular for men, a higher blood pressure variability at baseline was associated with a larger decrease in diastolic blood pressure during 1-year follow-up on placebo, explaining up to 2% of the variance of the observed changes. Similar associations were not observed for systolic blood pressure.

Optimal definition of daytime and night-time blood pressure.

OBJECTIVE: To review and categorize methods to define daytime and night-time blood pressures and to propose an optimal definition. METHODS: The methods can be divided into clock-time-independent and clock-time-dependent methods and, in addition, into wide methods, which use all pressure measurements for the entire 24 h period, and narrow methods, which exclude some of the measurements. RESULTS: The asleep and awake blood pressures, mostly defined as the in-bed and out-of-bed blood pressures, can be considered the optimum standard. Wide (square-wave fitting) and narrow (cumulative-sum analysis) clock-time-independent methods perform well with most subjects, but are problematic with reverse dippers because they identify periods of high and low blood pressure in these subjects that do not coincide with the day and the night. The results from fixed-time methods deviate from the awake and asleep blood pressures whens the predefined times do not coincide with the times subjects go to bed and arise; this is less of a problem for the narrow methods, in which data from morning and evening transition periods are discarded, than it is for the rigid time schedules of the wide methods. Reproducibilities of the various methods are roughly similar. CONCLUSION: We suggest that the optimal definition of daytime and night-time blood pressure is provided by the narrow clock-time-dependent method, in which data from morning and evening transition periods are excluded, because it is simple, reasonably accurate and reproducible and can be applied without disruption of the living habits of most subjects.

Blood pressure by Korotkoff's auscultatory method: end of an era or bright future?.

In 1905 Nicolay Korotkoff described the auscultatory technique of blood pressure measurement, which developed into and still remains the standard in clinical medicine. This review article retraces in short the history of indirect blood pressure measurement and Korotkoff's biography. This historical perspective illustrates how progress in science is achieved by open-minded men, who take up the unfinished ideas of their predecessors and inspire their followers. Conventional sphygmomanometry is fraught with potential sources of error, which may arise in the subject, the observer, the sphygmomanometer or the overall application of the technique. Single auscultatory readings are not representative of the blood pressure during the whole day and may be biased by the white-coat phenomenon. These drawbacks have provoked the development of alternative approaches to blood pressure measurement, both auscultatory and oscillometric. Among them, ambulatory monitoring and to a lesser extent the self-measurement of blood pressure have elicited the greatest enthusiasm. However, these newer methods serve only as accessories to Korotkoff's auscultatory method, when the latter produces doubtful results. Thus, the new methods of blood pressure measurement need not herald the end of Korotkoff's old technique, but may rather stimulate its more deliberate and frequent use in the future.

Ambulatory blood pressure monitoring in clinical trials.

Ambulatory blood pressure monitoring is increasingly being used in clinical trials. Trials with ambulatory monitoring, just like clinical experiments based on conventional sphygmomanometry, need to be controlled properly, because ambulatory blood pressure measurements are not completely devoid of placebo-like effects. The trough: peak ratio might be a useful instrument for assessment of the durations of action of antihypertensive drugs. However, its error term and confidence interval need to be reported and its determination in clinical trials requires further standardization. Ambulatory compared with conventional blood pressure measurements are characterized by a higher reproducibility. This property makes a reduction in sample size possible in cross-over but not in parallel group trials, if instead of the conventional blood pressure the 24 h or daytime blood pressures are compared. Trials focusing on the full course of the blood pressure through the day need a larger sample size than do those just concerning the conventional blood pressure level.

Conventional and ambulatory blood pressure measurement in older patients with isolated systolic hypertension:second progress report on the ambulatory blood pressure monitoring project in the Syst-Eur trial.

OBJECTIVES: To compare clinic and ambulatory blood pressure measurement and the reproducibility of these measurements in older patients with isolated systolic hypertension.PATIENTS: A total of 477 patients aged >/= 60 years with isolated systolic hypertension on clinic measurement were monitored during the placebo run-in phase of the Syst-Eur trial. METHODS: The time-weighted 24 h blood pressure, clock time day and night blood pressure, the cumulative sum-derived crest and trough blood pressure and the high and low blood pressure levels of the square-wave model were computed. The daily alteration between the high and low blood pressure spans was quantified using the clock time day-night difference, the cumulative sum-derived circadian alteration magnitude, the Fourier amplitude and the difference between the high and low blood pressure levels of the square-wave model. RESULTS: The daytime ambulatory systolic blood pressure was, on average, 21 mmHg lower than the clinic blood pressure, whereasthe diastolic blood pressure was, on average, similar with both techniques of measurement. In the 132 patients who underwent repeat measurements, clinic blood pressure levels and the parameters describing the difference betgween the daily high and low blood pressure spans were equally reproducible. However, both were less reproducible than the ambulatory blood pressure levels. The repeatability coefficients, expressed as percentages of near maximum variation, were 50 and 51% for the clinic systolic and diastolic blood pressures, 30 and 33% for the mean 24 h systolic and diastolic blood pressures and between 44 and 54% for the parameters describing the daily alteration between the high and low blood pressure spans. CONCLUSION: In older patients with isolated systolic hypertension, clinic and ambulatory systolic blood pressure may differ greatly; the prognostic significance of this difference remains to be elucidated. Furthermore, the level of blood pressure in these patients is more reproducible by ambulatory measurement than it is by clinic measurement.

An epidemiological approach to ambulatory blood pressure monitoring:the Belgian Population Study.

BACKGROUND: In order to determine reference values for ambulatory blood pressure, a random population sample of 1057 persons, 20-88 years old, was investigated in a geographically defined area of Belgium. This article is the final report on the cross-sectional phase of this population survey. METHODS:Twenty-four-hour ambulatory pressure was recorded at 20 min intervals from 0800 to 2200 h and at 45 min intervals from 2200 to 0800 h. Conventional blood pressure was measured by trained nurses at the participants' homes and also in a subgroup of 532 persons at a locally organized clinic. A conventional blood pressure exceeding 140 mmHg systolic or 90 mmHg diastolic and the taking of antihypertensive drugs were the criteria used to distinguish between normotensive and hypertensive persons. RESULTS: In the 1057 patients, of whom 328 were hypertensive, 24 h, daytime (2200 to 0800 h) and night-time (0000 to 0600 h) pressures averaged 119/71, 125/77 and 108/62 mmHg, respectively. Compared with daytime values, blood pressures at home were 3.5/1.5 mmHg lower in 729 normotensive people but 11.6/4.5 mmHg higher in 328 hypertensive patients. In the normotensive subgroup the 95th percentiles of the 24 h, daytime and night-time pressures were 129/80, 137/88 and 121/72 mmHg, respectively. These boundaries were not materially altered when we considered only the 275 participants who had been normotensive both at home and at the clinic (127/79, 135/87 and 118/72 mmHg, respectively). When, in addition to the Belgian data, other reports on large cohorts were also analysed, the transition from normotension to hypertension on ambulatory measurement was likely to be within the ranges of 130-135/80-85, 135-140/85-90 and 120-125/70-75 mmHg for 24 h, daytime and night-time pressures, respectively. CONCLUSION: In comparison with other population surveys and with the earlier interim reports on the Belgian study, the present analysis produced remarkably consistent results with respect to the distributions of the ambulatory measurements. The working definitions of normality based on the 95th percentiles of the ambulatory measurements in the normotensive participants in the present survey and various other studies need further validation in terms of the incidence of cardiovascular complications. For this purpose, the Belgian participants as well as other cohorts are being prospectively followed.