[Blood pressure variability]. / La variabilità della pressione arteriosa.

This review deals with a number of issues related to blood pressure variability. These include: historical aspects, with reference to the first pioneering observations; methodological aspects, focusing on the different methods for quantifying blood pressure variability; description of the characteristics of blood pressure variability over the 24 hours; mechanisms involved in determining the different magnitude of this phenomenon in different subjects, such as behavioral factors, central and reflex neural influences, humoral and mechanical factors; blood pressure variability as a probe to assess spontaneous baroreflex sensitivity; effects of aging and hypertension on blood pressure variability, with a discussion of the clinical relevance of this phenomenon in the prognostic evaluation of patients; effects of drugs on blood pressure variability. Finally methodological aspects related to the use of noninvasive ambulatory blood pressure monitoring in the assessment of blood pressure variability are discussed.

Smoking impairs baroreflex sensitivity in humans.

In 10 healthy smokers, finger blood pressure was recorded continuously for 1 h in a supine control condition and for 1 h while smoking four cigarettes, one every 15 min. Smoking increased average systolic blood pressure (+19%, P < 0.01) and its variability and reduced pulse interval (reciprocal of heart rate, -22%, P < 0.01) and its variability. Baroreflex sensitivity, as assessed by the slope of spontaneous hypertension/bradycardia or hypotension/tachycardia sequences and by the alpha-coefficient (squared ratio between pulse interval and systolic blood pressure spectral powers at 0.1 Hz) was significantly decreased (P < 0.01) during smoking, whereas there were no effects of smoking on the reflex changes in pulse interval induced by carotid baroreceptor stimulation through a neck suction device. Sham smoking by a drinking straw had no effects on any of the above parameters. Thus, when assessed in the absence of laboratory maneuvers in daily life conditions, baroreflex sensitivity is markedly impaired by smoking. This impairment may contribute to the smoking-induced increase in blood pressure and heart rate as well as to the concomitant alterations in their variability.

Performance of the AM-5600 blood pressure monitor: comparison with ambulatory intra-arterial pressure.

The AM-5600 is a new device that simultaneously monitors electrocardiogram (ECG) and noninvasive blood pressure (BP) over a 24-h period. BP readings (Korotkoff sounds and cuff air pressure) are stored into the recorder, allowing the removal of BP artifacts after a visual check. In 12 subjects with essential hypertension, we compared BP values simultaneously provided by the AM-5600 and intra-arterial recordings. At rest, noninvasive systolic BP (SBP) values were lower (5.4 +/- 4.9 mmHg) and diastolic BP (DBP) values were higher (7.3 +/- 7.3 mmHg) than were intra-arterial values. In ambulatory conditions (9 subjects), between-method discrepancies were +0.8 +/- 6.1 and +12.2 +/- 7.4 mmHg for 24-h SBP and DBP, respectively. AM-5600 underestimated 24-h intra-arterial SBP and DBP SD, but it accurately tracked intra-arterial SBP and DBP changes. Editing removed 22.1% of total readings, slightly reducing between-method discrepancies. Thus the AM-5600 provides an accurate average estimate of resting and ambulatory SBP and, for DBP, a less accurate estimate that is slightly improved by editing. The AM-5600 allows accurate description of SBP and DBP profiles and thus may be suitable to describe the abrupt BP changes accompanying a number of clinical events.

Blood pressure reduction and end-organ damage in hypertension.

VALUE OF AMBULATORY BLOOD PRESSURE MONITORING: Studies that have used ambulatory blood pressure monitoring techniques have shown that the average 24-h or daytime blood pressure values are more closely related to the end-organ damage associated with hypertension than are isolated office readings. IMPORTANCE OF BLOOD PRESSURE VARIABILITY IN PROGNOSIS: More recently, blood pressure variability, measured as the overall 24-h blood pressure standard deviation, has been shown to have a significant relationship to end-organ damage in hypertensive patients. The potential clinical relevance of blood pressure variability has been strengthened in a recent prospective study. The possible prognostic value of blood pressure variability has practical implications for antihypertensive treatment; it may mean, for example, that the optimal antihypertensive drug should reduce not only the mean 24-h values but also the degree of fluctuation in blood pressure. This is more likely to occur with long-acting drugs, which induce a more balanced reduction in blood pressure throughout the 24 h. USE OF THE TROUGH:PEAK RATIO: A proposed measure of a balanced 24-h blood pressure effect is the trough:peak ratio of the blood pressure fall. This ratio can be obtained by clinic blood pressure measurements but ambulatory blood pressure monitoring offers some distinct advantages. One of these advantages is that by revealing the possibility of an excessive fall in blood pressure at the time of the peak effect or an uncontrolled rise at the trough, ambulatory monitoring can also reveal the possible impact of pharmacological treatment on 24-h blood pressure variability.

Blood pressure variability: clinical implications and effects of antihypertensive treatment.

HYPOTHESIS ON RELATIONSHIP BETWEEN BLOOD PRESSURE VARIABILITY AND END-ORGAN DAMAGE: Several studies have shown that the cardiovascular complications of hypertension are more closely related to ambulatory 24-h or daytime average blood pressure than to office readings. A few studies have also provided evidence that in hypertensive patients, not only average ambulatory blood pressure but also the degree of blood pressure variability is significantly and independently related to the end-organ damage associated with hypertension. LIMITATIONS OF PREVIOUS STUDIES: A common limitation of previous studies is that they were based on cross-sectional or retrospective observations, so that the correlative evidence they provide does not allow the relationship between blood pressure variability and end-organ damage to be interpreted causally. EVIDENCE FROM RECENT STUDIES: Recent evidence from follow-up observations has strongly supported the hypothesis that blood pressure variability is prognostically important in hypertensive patients. These findings suggest that optimal antihypertensive treatment should aim not only to reduce mean blood pressure levels, but also to reduce the degree of blood pressure fluctuation. EFFECTS OF ANTIHYPERTENSIVE DRUGS: Unfortunately, while most new antihypertensive drugs seem to be effective in reducing 24-h mean blood pressure levels, they are frequently unable to reduce 24-h blood pressure variability, which is often increased during treatment when expressed in normalized units. The development of drugs that guarantee a constant and uniform reduction in blood pressure over 24 h may, in principle, offer a further advantage by preventing the increase in 24-h blood pressure fluctuations that may follow the administration of short-acting antihypertensive agents. TROUGH: PEAK MEASUREMENTS OF BLOOD PRESSURE: The trough: peak ratio, proposed as an arithmetic indicator of the duration of the antihypertensive effect of a drug, may be a useful measure of the occurrence of a smooth reduction in blood pressure over 24 h. The possibility of obtaining an additional reduction in cardiovascular risk for hypertensive patients by minimizing the net trough: peak effect of antihypertensive drugs is thus an important issue for future studies.

Noninvasive automatic blood pressure monitoring does not attenuate nighttime hypotension. Evidence from 24 h intraarterial blood pressure monitoring.

Automatic ambulatory blood pressure monitoring makes use of repeated cuff inflations throughout the day and night. This may interfere with the cardiovascular effects of sleep and thus alter the 24 h blood pressure profile. The possibility that intermittent automatic blood pressure measurements prevent nocturnal hypotension was examined in 17 mild or moderate essential hypertensive patients in whom blood pressure was recorded intraarterially for 48 h by the Oxford technique. During the first or the second 24 h period, blood pressure was also monitored noninvasively by the SpaceLabs (Redmond, WA) 5300 (n = 10) and by the Sandoz Pressure System SPS 1558 (Lavanchy Electronique, Prilly, Switzerland) (n = 7) devices, automatic measurements being performed at 15 min intervals during the day and at 30 min intervals during the night. Separate computer analysis of 24 h intraarterial tracings obtained in absence and in concomitance of contralateral automatic blood pressure monitoring showed that the occurrence of automatic measurements had not interfered with the day-night intraarterial blood pressure and heart rate profiles. Thus the frequent cuff inflations that characterize automatic blood pressure monitoring do not attenuate nighttime hypotension and bradycardia. This finding supports use of the noninvasive approach in assessing blood pressure profiles.

Evaluation of noninvasive blood pressure monitoring devices Spacelabs 90202 and 90207 versus resting and ambulatory 24-hour intra-arterial blood pressure.

This study evaluated the accuracy of blood pressure values provided by the Spacelabs 90202 and 90207 devices in comparison with intra-arterial recording in 19 subjects at rest and in nine subjects in ambulatory conditions (Oxford method). At rest Spacelabs monitors reflected intra-arterial systolic blood pressure values very closely but overestimated to a considerable extent intra-arterial diastolic blood pressure (Spacelabs-intra-arterial differences, -0.8 +/- 9.2, NS, and 9.1 +/- 8.8 mm Hg, p less than 0.01, for systolic and diastolic blood pressures, respectively). In ambulatory conditions Spacelabs-intra-arterial average differences in 24-hour values were +0.4 +/- 5.1 mm Hg for systolic blood pressure (NS) and +14.0 +/- 2.9 mm Hg for diastolic blood pressure (p less than 0.01) when group data were considered. The performance of both Spacelabs devices was worse when assessed in individual subjects or for each hourly interval. In spite of these differences between noninvasive and intra-arterial absolute blood pressure values, however, Spacelabs 90202 and 90207 monitors were able to faithfully reflect directional hour-to-hour changes in intra-arterial blood pressure (chi 2 = 18.2 and chi 2 = 23.1 for systolic and diastolic blood pressures, respectively, p less than 0.01). No differences were found between the performance of the two Spacelabs devices. Thus, although the absolute accuracy of blood pressure values provided by these monitors in ambulatory subjects is still limited, they seem to be suitable for studies aimed at assessing 24-hour blood pressure profiles quantitatively as well as qualitatively.

Persistent blood pressure increase induced by heavy smoking.

OBJECTIVE: To test the hypothesis that heavy smoking is associated with a persistent increase in blood pressure. DESIGN: In 10 normotensive smokers asked to smoke one cigarette every 15 min for 1 h, blood pressure and heart rate were continuously monitored during the smoking period and during the preceding non-smoking hour. In six other normotensive smokers asked to smoke two cigarettes per hour throughout the whole day, blood pressure and heart rate were monitored non-invasively in ambulatory conditions for 8 h (0900-1700 h). Blood pressure monitoring was repeated during a non-smoking day. METHODS: Beat-to-beat blood pressure and heart rate were monitored at rest by means of the Finapres device. Blood pressure signal was sampled at 165 Hz by a computer to calculate hourly data. Ambulatory blood pressure and heart rate were measured once every 10 min. RESULTS: In resting conditions, the first cigarette caused an immediate and marked increase in blood pressure and heart rate, and the peak blood pressure and heart rate achieved were similar for the remaining three cigarettes. In each instance, the hemodynamic effects were so prolonged that throughout the smoking hour, blood pressure and heart rate were persistently higher than during the non-smoking hour. The standard deviations of systolic and diastolic blood pressure and heart rate were also higher during the smoking hour, indicating an increase in blood pressure and heart rate variability. In the six ambulant smokers, daytime blood pressure and heart rate were also persistently higher during smoking than during non-smoking. CONCLUSIONS: Heavy smoking is associated with a persistent rise in blood pressure and also with an increase in blood pressure variability. These effects (which may escape clinic blood pressure measurements performed during non-smoking) may account for some of the smoking-related cardiovascular risk.

Testing the accuracy of blood pressure monitoring devices in ambulatory conditions.

In recent years technological progress has improved the construction of ambulatory blood pressure monitoring devices. This has resulted in devices able to measure blood pressure continuously and non-invasively, and also in lighter, less noisy and more accurate intermittent blood pressure monitors. The accuracy of monitors, however, is still tested by taking blood pressure measurements at rest, and testing against intra-arterial blood pressure values, in true ambulatory conditions, is very seldom used. When evaluated by the latter approach, devices such as SpaceLabs 5300 and the Sandoz SPS 1558 recorders can be substantially inaccurate. Newer devices such as the SpaceLabs 90202 and 90207 are also somewhat inaccurate, particularly when diastolic blood pressure is considered. However, hour-to-hour changes in blood pressure obtained by the SpaceLabs 90202 and 90207 monitors are qualitatively and quantitatively similar to those obtained by invasive methods. This makes it possible to describe the 24-h blood pressure profile more accurately.

Effect of stress on diagnosis of hypertension.

Blood pressure assessment by a physician elicits an alerting reaction and a pressor response in the patient. The magnitude and time course of this response are described for a large number of hypertensive subjects in whom the assessments were performed during ambulatory intra-arterial blood pressure monitoring. In nearly all of the subjects, the physician's visit was accompanied by blood pressure and heart rate increases that peaked within 4 minutes and then declined. The response was characterized by a relatively high average value; a large between-subject variability; no relation with patient age, baseline hemodynamic values, and responses to laboratory stressors; and no attenuation with multiple repetition of the physician's visit. On the other hand, the increase in blood pressure was considerably less when blood pressure assessment was made by a nurse than when it was made by a physician; in both instances, a 10-minute wait was associated with marked reduction of the initial response. Thus, the stress inherent in usual blood pressure-measuring procedures is responsible for considerable overestimations of patients' blood pressures. There are means by which this can be minimized, although a residual error is likely to remain in most subjects. Whether the stress-devoid blood pressure is a better prognostic index than the stress-related one remains unknown.

24-hour blood pressure monitoring in hypertension.

It has been recognized for some time that blood pressure is highly variable over a 24-h period. A number of studies have demonstrated that the extent and severity of target-organ damage associated with hypertension can be correlated more closely with blood pressure values monitored continuously for 24 h than with individual values recorded sphygmomanometrically. A great deal of interest is focused on whether absolute values of diastolic or systolic blood pressure, values during the day or night, or the rate of change of blood pressure such as the rapid increase that occurs in the early morning are more or less important factors contributing to the mortality and morbidity associated with hypertension. Work from our own unit provides evidence of the importance of two features in the variability of blood pressure. Blood pressure decreases during the night, but remains higher in hypertensive patients than in normotensive subjects. The mean nighttime blood pressure was shown to correlate with hypertension-related target-organ damage almost as closely as the mean daytime blood pressure. Using 24-h blood pressure monitoring, we have shown that the higher the mean 24-h blood pressure, the greater the extent and severity of target-organ involvement. In addition, for patients with comparable mean 24-h blood pressure values, larger degrees of blood pressure variability throughout the monitoring period were associated with more target-organ damage. Taking the available evidence into account, it is probably important that treatments used for hypertension should provide control of blood pressure for a full 24-h period confirmed by ambulatory blood pressure monitoring.

Blood pressure and heart rate response to repeated smoking before and after beta-blockade and selective alpha 1 inhibition.

In normotensive volunteers who habitually smoked more than 20 cigarettes a day, 1-h beat-to-beat blood pressure recordings were taken. Measurements were made using a non-invasive finger device when the subjects were not smoking (1 h, control) and during an hour in which the subjects were asked to smoke four cigarettes, one every 15 min. The first cigarette smoked produced a marked increase in systolic and diastolic blood pressures and the heart rate. The peak blood pressure and heart rate values observed for the first cigarette did not change when the remaining three cigarettes were smoked, indicating that the responses were neither attenuated nor increased by repeated smoking. However, after each cigarette, the pre-smoking values did not return to baseline, but were successively greater for the second, third and fourth cigarettes, indicating that blood pressure and the heart rate undergo a persistent increase during smoking. Compared with the hour-long non-smoking period, mean values over the smoking period were 18.8%, 14.0% and 29.7% higher for systolic and diastolic blood pressure and the heart rate, respectively. Cigarette smoking also increased the blood pressure and heart rate standard deviations around the mean, thereby increasing the variability. The effects of atenolol and doxazosin on the blood pressure and heart rate responses to smoking were investigated in two placebo-controlled, single-blind, randomly allocated, crossover studies. Compared with placebo, atenolol (50-100 mg given once a day for 4 days) significantly attenuated the smoking-induced increase in the heart rate but not the increase in systolic or diastolic blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular effects of smoking.

Coronary heart disease (CHD) increases with smoking and this factor interacts with hypercholesterolemia and hypertension in raising the incidence of this condition in a greater than linear fashion. This can be explained by the adverse effect of smoking on plasma fibrogen, platelet turnover and lipid profile. It may also be accounted for, however, by the acute bradycardia, increase in blood pressure and generalized vasoconstriction accompanying smoking, due to a nicotine-dependent activation of the sympathetic nervous system. These effects (which in heavy smokers can raise blood pressure permanently) are only partly offset by beta-blockers and can only be abolished by opposing the cardiac and vascular sympathetic influences by alpha and beta-blockade combined.

Early twenty-four-hour blood pressure elevation in subjects with parental hypertension.

We studied 15 normotensive offspring of hypertensive parents, comparing them with 15 normotensive controls matched for sex, body mass index and age. In the offspring, both parents were hypertensive, while in the controls, neither parent was hypertensive. Blood pressure was measured at rest, during a variety of laboratory stressors (mental arithmetic, mirror drawing test, hand grip and cold pressor test), and was also monitored for 24 h in ambulatory conditions (Spacelabs 5300 M, Richmond, Washington, USA). Resting mean and diastolic blood pressures were higher (P less than 0.05) in the subjects with parental hypertension than in those without. The mean blood pressure rise induced by the laboratory stressors was not significantly greater at any time in the subjects with hypertensive parents compared with controls. Twenty-four-hour systolic and mean blood pressures, however, were significantly higher (P less than 0.05) in the subjects with hypertensive parents than in the controls. Thus the higher office blood pressure shown in the prehypertensive stage by subjects with parental hypertension is not due to hypersensitivity to stress, but represents an early and permanent blood pressure elevation.

Comparison of finger and intra-arterial blood pressure monitoring at rest and during laboratory testing.

The accuracy of blood pressure values obtained by continuous noninvasive finger blood pressure recording via the FINAPRES device was evaluated by comparison with simultaneous intraarterial monitoring both at rest and during performance of tests known to induce fast and often marked changes in blood pressure. The comparison was performed in 24 normotensive or essential hypertensive subjects. The average discrepancy between finger and intra-arterial blood pressure recorded over a 30-minute rest period was 6.5 +/- 2.6 mm Hg and 5.4 +/- 2.9 mm Hg for systolic and diastolic blood pressure, respectively; a close between-method correspondence was also demonstrated by linear regression analysis. The beat-to-beat changes in finger systolic and diastolic blood pressure were on average similar to those measured intra-arterially during tests that induced a pressor or depressor response (hand-grip, cold pressor test, diving test, Valsalva maneuver, intravenous injections of phenylephrine and trinitroglycerine) as well as during tests that caused vasomotor changes without major variations in blood pressure (application of lower body negative pressure, passive leg raising). The average between-method discrepancy in the evaluation of blood pressure changes was never greater than 4.3 and 2.0 mm Hg for systolic and diastolic blood pressure, respectively; the corresponding standard deviations ranged between 4.6 and 1.6 mm Hg. Beat-to-beat computer analysis of blood pressure variability over the 30-minute rest period provided standard deviations almost identical when calculated by separate consideration of intra-arterial and finger blood pressure tracings (3.7 and 3.8 mm Hg, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Twenty-four hour ambulatory intra-arterial blood pressure in normotensive and borderline hypertensive subjects.

A number of studies have shown that blood pressure values obtained by ambulatory monitoring are lower than those obtained in the doctor's office by cuff readings. However, there is still no suitable information on 'normal' 24-h ambulatory blood pressure values. In 19 normotensive and 13 borderline hypertensive subjects, defined by repeated office blood pressure measurements, we recorded intra-arterial blood pressure under ambulatory conditions for 24 h (Oxford method) in order (1) to assess the 24-h blood pressure values of normal subjects, and (2) to compare their 24-h blood pressure values with those of borderline hypertensive patients. In the normotensive subjects systolic, diastolic and mean ambulatory blood pressure values over 24 h were significantly lower than the corresponding office values, the differences being -15.0, -22.1 and -17.9 mmHg, respectively. In the borderline hypertensives 24-h ambulatory blood pressure was significantly lower than office readings. On average, the 24-h mean blood pressure of normotensive subjects was significantly lower than that of borderline patients (P less than 0.01). However, individual 24-h blood pressure values showed a considerable overlap. Thus, (1) ambulatory blood pressure values just below 140/90 mmHg do not necessarily mean that the blood pressure is in the normal range, the mean 24-h blood pressure of true normotensive subjects being much lower; (2) ambulatory blood pressure monitoring in patients with high office blood pressure readings may help to identify subjects whose 24-h mean values are indistinguishable from those of normotensives. However, the clinical relevance of these findings in the diagnosis of hypertension has to be validated by prospective clinical trials.

24-hour blood pressure monitoring: evaluation of Spacelabs 5300 monitor by comparison with intra-arterial blood pressure recording in ambulant subjects.

The accuracy of 24-h blood pressure values obtained by ambulatory monitoring via the Spacelabs 5300 device was evaluated by comparison with simultaneous 24-h intra-arterial blood pressure recording from the contralateral arm. The comparison was made in eight essential hypertensive subjects in whom non-invasive blood pressure was measured every 15 (day) or 30 min (night). The measurements were automatically and visually edited to eliminate artefactual readings and hourly and 24-h means were calculated separately for systolic and diastolic blood pressure. The corresponding intra-arterial blood pressure means were also calculated. In the group as a whole, hourly means obtained by the non-invasive device were similar or only slightly different from those recorded intra-arterially. The 24-h systolic blood pressure mean obtained non-invasively was not significantly different from that obtained intra-arterially (138.4 +/- 9.1 and 142.9 +/- 9.2 mmHg, respectively), nor were the corresponding 24-h diastolic blood pressure means significantly different (83.5 +/- 4.5 and 80.6 +/- 3.5 mmHg, respectively). However, in spite of these similarities, there were contrasting and often large discrepancies between non-invasive and intra-arterial values in individual subjects. For the 24-h systolic blood pressure mean the discrepancies ranged from 7.6 +/- 1.1 to 16.1 +/- 2.2 mmHg and for the 24-h diastolic blood pressure mean, from 3.5 to 13.2 mmHg. Thus, the Spacelabs 5300 device has a limited ability to correctly estimate ambulatory blood pressure in individual subjects. It may be better suited for the estimation of group blood pressures, but only because errors are smoothed by the summation of individual errors of opposing signs.

Evaluation of the baroreceptor-heart rate reflex by 24-hour intra-arterial blood pressure monitoring in humans.

The baroreceptor control of the sinus node was evaluated in 10 normotensive and 10 age-matched essential hypertensive subjects in whom ambulatory blood pressure was recorded intra-arterially for 24 hours and scanned by a computer to identify the sequences of three or more consecutive beats in which systolic blood pressure (SBP) and pulse interval (PI) progressively rose (+PI/+SBP) or fell (-PI/-SBP) in a linear fashion, according to a method validated in cats. In normotensive subjects, several hundred +PI/+SBP and -PI/-SBP sequences of 3 beats were found whereas the number of sequences of 4, 5, and more than 5 beats showed a progressive drastic reduction. The mean slopes of +PI/+SBP (7.6 +/- 2.0 msec/mm Hg) and -PI/-SBP (6.4 +/- 1.5 msec/mm Hg) sequences were similar, but in both instances there was a large scattering of the values around the mean (variation coefficients: 64.2 +/- 4.7 and 62.6 +/- 2.4%). The slopes decreased as a function of the sequence length and baseline heart rate and increased to a marked extent during the night as compared with daytime values. All sequences were more rare (-33.2% for +PI/+SBP and -31.7% for -PI/-SBP) and less steep in hypertensive subjects (-40.3 and -36.2%, respectively), who failed to show the marked nighttime increase in slope observed in normotensive subjects. To our knowledge, these observations provide the first description in humans of the baroreceptor-heart rate reflex in daily life. This reflex is characterized by marked within-subject variations in sensitivity due in part to hemodynamic, temporal, and behavioral factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the cardiovascular effects of different laboratory stressors and their relationship with blood pressure variability.

Laboratory stressors are employed to assess the 'typical' cardiovascular reactivity to stress of a given subject. It is believed that this may assist in the diagnosis of hypertension and predict future development of blood pressure (BP) elevation. However, the internal consistency of the data obtained by laboratory stressing manoeuvres and their ability to reflect the effects of everyday stressful events occurring over a 24-h period have never been clearly established. We studied a group of ambulant normotensive and essential hypertensive in-patients who were undergoing prolonged intra-arterial blood pressure monitoring (Oxford method) to determine firstly, whether four routine laboratory stressors provided a homogeneous evaluation of subjects' reactivity and secondly, whether cardiovascular reactivity to these stressors reflected a tendency of BP to vary over a 24-h period. A significant correlation (P less than 0.01) was found between the pressor responses to mental arithmetic and the mirror drawing test and between the pressor responses to the cold pressor test and hand-grip. These correlations, however, were not close and responses to the 'mental' and 'physical' stressors were unrelated. The elevation in BP induced by laboratory stressors also did not correlate with the increase in BP accompanying stress elicited outside laboratory conditions (i.e. doctor's visit). The pressor effects of both the laboratory and the out-of-laboratory stressors showed little or no correlation with the 24-h absolute or per cent blood pressure variabilities, although for the stressors involving a mental challenge, a significant though not close correlation with daytime blood pressure variability was found. These data underline the limitations of laboratory tests in assessing cardiovascular reactivity to stress.(ABSTRACT TRUNCATED AT 250 WORDS)