Age-related differences of blood pressure profile in essential hypertension

Peak blood pressure-guided monitoring may serve as an effective approach for blood pressure control in the out-of-office setting

We aimed to explore whether diurnal blood pressure (BP) peak characteristics have a significant influence on the association between left ventricular damage with the two BP components (morning BP vs. afternoon peak BP) in untreated hypertensives. This cross-sectional study included 1084 hypertensives who underwent echocardiography and 24-h ambulatory BP monitoring. Participants were stratified according to the relationship between morning systolic BP (MSBP; average SBP within 2 h of waking up) and afternoon peak systolic BP (ASBP; average SBP between 16:00 and 18:00). Afternoon and morning hypertension was defined as ≥ 135/85 mm Hg. The morning and afternoon peak BPs occurred at around 7:00 and 17:00, respectively. In general hypertensives, morning BP and afternoon peak BP are significantly different in absolute values (for binary SBP, McNemar's χ²  = 6.42; p = .014). ASBP was more pronounced than MSBP in 602 patients (55.5%), in whom 24-h SBP showed higher consistency with ASBP than with MSBP (Kappa value: 0.767 vs 0.646, both p < .01). In subjects with ASBP ≥ MSBP, ASBP was associated with left ventricular hypertrophy independent of MSBP (logistic regression analysis odds ratio: 1.046, p < .01), and left ventricular mass index was more strongly correlated with ASBP than with MSBP (multiple regression coefficient β: 0.453, p < .01), in which the relationships held true independently of 24-h SBP. The opposite results were obtained in subjects with MSBP > ASBP. Peak BP-guided monitoring may serve as an effective approach to out-of-office hypertension monitoring and control, providing the best consistency with 24-h average SBP and highest discrimination performance for target organ damage, independently of 24-h SBP.

Afternoon blood pressure increase: a blood pressure pattern associated with microvascular complications in type 2 diabetes mellitus

BACKGROUND

Minor blood pressure (BP) alterations detected by ambulatory BP monitoring (ABPM) was associated with microvascular disease in type 2 diabetes mellitus (DM). We examined whether a previously described afternoon BP peak is linked to hypertension status and associated with microvascular complications.

METHODS

A cross-sectional study was conducted with 207 type 2 DM patients (56 years, 52.7% men). ABPM was determined by oscillometry.

RESULTS

An increase in both systolic and diastolic BP occurred in the afternoon; the same pattern was observed across hypertension categories (normotensive, prehypertensive, or hypertensive). We calculated BP increase for the period between 2 and 8 PM as the difference between mean BP at 8 PM and mean BP at 2 PM (calculated by the average of four measurements in each hour). The cohort was then divided into two groups (afternoon BP increase below or above the group's median). The prevalence of diabetic retinopathy (DR) was higher in those with afternoon increment above the group median for both systolic (50 vs. 30%, P = 0.004) and diastolic (47 vs. 33%, P = 0.04) BP. For systolic BP, this result was maintained after adjustments for age, gender, A1c test, DM duration, total cholesterol, and 24-h systolic BP. Afternoon BP increments for both systolic and diastolic BP correlated significantly with urinary albumin excretion rate (UAER) after adjusting for 24-h BP (systolic: r = 0.17, P = 0.01; diastolic: r = 0.16, P = 0.02). However, when adjusted for all covariates, these correlations were no longer significant.

CONCLUSIONS

An increment in afternoon BP was observed in type 2 diabetic patients regardless of hypertension status; that increment was associated with higher prevalence of DR but not diabetic nephropathy independently of measured confounders.

24-hour variation in the reactivity of rate-pressure-product to everyday physical activity in patients attending a hypertension clinic

The exercise-related response of the rate-pressure-product (RPP) is a prognostic marker of autonomic imbalance, cardiovascular mortality, and silent myocardial ischemia in hypertension. In view of the well-known 24 h variation in out-of-hospital sudden cardiac events, our aim was to investigate whether the reactivity of RPP to everyday physical activities varies over the 24 h. Ambulatory measurements of systolic blood pressure (BP) and heart rate were recorded every 20 min for 24 h in 440 diurnally active patients attending a hypertension clinic. Wrist activity counts were summed over the 15 min that preceded a BP measurement. An RPP reactivity index was derived for each of twelve 2 h data bins by regressing the change in RPP against the change in logged activity counts. The RPP showed 24 h variation (p < 0.0005), with a peak of 11,004 (95% CI = 10,757 to 11,250) beat . min(-1) . mmHg occurring at 10:00 h (2 h after mean wake-time). The overall 24 h mean of RPP reactivity was 477 beat . min(-1) . mmHg . logged activity counts(-1) (95% CI = 426 to 529). The largest increase in RPP reactivity occurred within the first 2 h after waking (p < 0.0005). There were no subsequent significant differences in RPP reactivity up to 14 h after waking. The lowest RPP reactivity was found 18-20 h after waking, with a peak-to-trough variation of 593 beat . min(-1) . mmHg . logged activity counts(-1) (95% CI = 394 to 791, p < 0.0005). Although this variation was not moderated by BP status, age, or sex, less variability in RPP reactivity was found for the medicated individuals during the waking hours. These data suggest that under conditions of normal living, the reactivity of RPP to a given change in physical activity increases markedly during the first 2 h after waking from nocturnal sleep, the time when out-of-hospital sudden cardiac events are also most common. Therefore, these data add weight to the notion that reactivity of RPP to physical activity could be a prognostic marker of autonomic imbalance and cardiovascular mortality, although more research is needed to assess the specific prognostic value of 24 h ambulatory measurements of RPP and physical activity.

Seasonal influence on blood pressure in elderly normotensive subjects

The aim of this study was to examine whether or not fluctuations in blood pressure (BP) differ by season. Subjects were 45 elderly individuals (20 men and 25 women; mean age, 66.5+/-4.9 [SD] years). Each subject's BP was recorded with an ambulatory BP monitoring device for 24 h during each of the four seasons. Subjects also wore a portable weather meter to obtain ambient temperature, relative humidity, and barometric pressure simultaneously with BP. The relationships between meteorologic values and BP were investigated at various parts of the day. Seasonal differences in BP fluctuation around wake-up-time were analyzed by means of the Tukey's test. The difference between the pre-wake-up-time systolic BP and the wake-up-time systolic BP was significantly greater in winter than in summer (8.7 mmHg greater, p<0.001). The difference between pre-wake-up-time and wake-up-time systolic BP was significantly greater in autumn than in spring (9.4 mmHg greater, p<0.001) or summer (13.1 mmHg greater, p<0.001). The difference between pre-wake-up-time heart rate and wake-up-time heart rate did not differ statistically between seasons. In conclusion, the present study showed that the difference between pre-wake-up-time systolic BP and wake-up-time systolic BP was greatest in the colder seasons, i.e., autumn and winter. There appears to be a large fluctuation in wake-up-time in the colder seasons. Low ambient temperature likely induces this large fluctuation.

Relationships between sleep, physical activity and human health

Although sleep and exercise may seem to be mediated by completely different physiological mechanisms, there is growing evidence for clinically important relationships between these two behaviors. It is known that passive body heating facilitates the nocturnal sleep of healthy elderly people with insomnia. This finding supports the hypothesis that changes in body temperature trigger somnogenic brain areas to initiate sleep. Nevertheless, little is known about how the core and distal thermoregulatory responses to exercise fit into this hypothesis. Such knowledge could also help in reducing sleep problems associated with nocturnal shiftwork. It is difficult to incorporate physical activity into a shiftworker's lifestyle, since it is already disrupted in terms of family commitments and eating habits. A multi-research strategy is needed to identify what the optimal amounts and timing of physical activity are for reducing shiftwork-related sleep problems. The relationships between sleep, exercise and diet are also important, given the recently reported associations between short sleep length and obesity. The cardiovascular safety of exercise timing should also be considered, since recent data suggest that the reactivity of blood pressure to a change in general physical activity is highest during the morning. This time is associated with an increased risk in general of a sudden cardiac event, but more research work is needed to separate the influences of light, posture and exercise per se on the haemodynamic responses to sleep and physical activity following sleep taken at night and during the day as a nap.

Chronobiological considerations for exercise and heart disease

Although regular physical activity is beneficial for many clinical conditions, an acute bout of exercise might increase the risk of an adverse clinical event, such as sudden cardiac death or myocardial infarction, particularly in vulnerable individuals. Since it is also known that the incidence of these events peaks in the morning and that some cardiac patients prefer to schedule leisure-time physical activity before lunch, the question arises as to whether morning exercise is 'inherently' more risky than physical activity performed at other times of day. We attempt to answer this question by reviewing the relevant epidemiological data as well as the results of chronobiological and exercise-related studies that have concentrated on the pathophysiological mechanisms for sudden cardiac events. We also consider generally how chronobiology might impact on exercise prescription in heart disease. We performed a structured literature search in the PubMed and WEBofSCIENCE databases for relevant studies published between 1981 and 2004. The limited amount of published epidemiological data did not allow us to conclude that a bout of vigorous exercise in the morning increases the relative risk of either primary cardiac events in apparently healthy individuals, or secondary events in cardiac patients enrolled in supervised exercise programmes. Nevertheless, these data are not directly relevant to individuals who have a history of heart disease and perform uncontrolled habitual activities. It appears as though the influence of time of day on the cardiovascular safety of this type of exercise has not been examined in this population. There is evidence that several pathophysiological variables (e.g. blood pressure, endothelial function, fibrinolysis) vary in parallel with typical diurnal changes in freely chosen activity. Nevertheless, few studies have been designed to examine specifically whether such variables respond differently to a 'set' level of exercise in the morning compared with the afternoon or evening. Even fewer researchers have adequately separated the influences of waking from sleep, adopting an upright posture and physical exertion per se on these pathophysiological responses at different times of day. In healthy individuals, exercise is generally perceived as more difficult and functional performance is decreased in the morning hours. These observations have been confirmed for patients with heart disease in only one small study. It has also not been confirmed, using an adequately powered study involving cardiac patients, that the responses of heart rate and oxygen consumption (VO(2)) to a set bout of exercise show the highest reactivity in the afternoon and evening, which is the case with healthy individuals. Confirmation of this circadian variation would be important, since it would mean that exercise might be prescribed at too high an intensity in the morning if heart rate or VO(2) responses are employed as markers of exercise load. We conclude that there is some parallelism between the diurnal changes in physical activity and those in the pathophysiological mechanisms associated with acute cardiac events. Nevertheless, more studies are needed to ascertain whether the responses of endothelial function, fibrinolysis and blood pressure to a set exercise regimen differ according to time of day. The results of epidemiological studies suggest that morning exercise is just as safe as afternoon exercise for cardiac patients enrolled in a supervised rehabilitation programme. Nevertheless, it is unclear whether time of day alters the risk of a cardiac event occurring during spontaneous physical activity performed by individuals with established risk factors for heart disease.

Reactivity of Ambulatory Blood Pressure to Physical Activity Varies With Time of Day

Blood pressure (BP) fluctuates over a 24-hour period, but it is unclear to what extent this variation is governed completely by changes in physical activity. Our aim was to use a BP “reactivity index” to investigate whether the BP response to a given level of physical activity changes during a normal sleep-wake cycle. Hypertensive patients (n=440) underwent simultaneous 24-hour ambulatory BP, heart rate (HR), and activity monitoring. BP and HR were measured every 20 minutes. Actigraphy data were averaged over the 15 minutes that preceded a BP measurement. Individual BP and HR reactivity indices were calculated using least-squares regression for twelve 2-hour periods. These indices were then analyzed for time-of-day differences using a general linear model. Systolic BP and HR were generally more reactive to physical activity than diastolic BP. The highest reactivity of systolic BP (mean±SE=4±1 mm Hg per logged unit change in activity) was observed between 8:00 am and 10:00 am ( P =0.014). Between 10:00 am and 12:00 pm , BP reactivity then decreased ( P =0.048) and showed a secondary rise in the early afternoon. These 24-hour changes in BP reactivity did not differ significantly between groups formed on the basis of early and late wake times ( P =0.485), medication use, age, and sex ( P >0.350). In conclusion, under conditions of normal living, the reactivity of BP and HR to a given unit change in activity is highest in the morning and shows a secondary rise in the afternoon.