Circadian Variation of Hemodynamics and Baroreflex Functions in Patients with Essential Hypertension.

Abstract

It is well known that cardiovascular accidents such as myocardial infarction frequently occur in the morning, but their triggering mechanisms are not clear. The present study investigated circadian variations of hemodynamics and baroreflex functions. Twenty-three patients with essential hypertension were studied. Direct blood pressure (BP) and ECG were recorded by telemeter over 24 h, and then computeranalyzed. The pulse-contour method was used to measure cardiac output (CO) and total peripheral vascular resistance (TPR). The ratio of low to high frequency components (LF/HF) of the RR-interval on ECG was calculated by power spectral analysis. The baroreflex sensitivity index (BR!) was measured on the basis of the ratio d RR/LI Ps (zl Ps= spontaneous decrease in systolic BP, zl RR = change in RR). Furthermore, 24-h BP changes were transformed algebraically into positive load component (PC) and negative load component (NC) by using a Windkessel model. The circadian variation of hematocrit (Ht) was also measured. The least squares method was used to determine the time at which the maximum and minimum value of each measurement occurred. Whereas the maximum values for BP and CO occurred in the evening (18:30, 17:00), the maximum values for TPR and LF/HF occurred between 06:30 and 08:00, and the minimum value for BRI occurred at 08:00. PC significantly correlated with Ps, heart rate, and CO (r=0.81, 0.92, 0.67), and NC significantly correlated with BRI and LFIHF (r=0.71, 0.64). PC (related to cardiovascular function) reached a maximum and NC (related to baroreflex function) reached a minimum in the late morning (11:00). Ht was highest immediately after the subjects got out of bed. These hemodynamic imbalances may negatively influence coronary blood flow in the morning. (Hypertens Res 1997; 20: 157-166)

Diurnal Variation in the Mechanical and Neural Components of the Baroreflex

“…35 Studies using spontaneous baroreflex indices have consistently shown that the highest sensitivities occur during the night, with reduced sensitivities in the morning after waking. 10,12,13,33 However, the variations during the daytime have not been consistent between studies. For example, Tochikubo et al 12 found the circadian variation to be bimodal with a secondary peak in baroreflex sensitivity at 7:00 PM and trough at 11:00 PM.…”

“…10,12,33,34 Hossmann et al 14 were the first to investigate baroreflex sensitivity changes over a full 24-hour period, which was examined at 3-hour intervals using l-noradrenaline infusions to perturb BP. Although the times of the trials do not coincide precisely with those of this study, our 7:00 AM trial is broadly comparable with their 9:00 AM trial, a time in which they also reported low baroreflex sensitivity.…”

Effects of Pulse-Synchronized Massage With Air Cuffs on Peripheral Blood Flow and Autonomic Nervous System

“…The Frank formula 12 is as follows: BP = cardiac output × TPR = SV× HR × TPR, where TPR = total peripheral vascular resistance. We consider it is possible that HR and TPR decrease as a baroreflex action 13 in order to maintain a steady BP during the PS-AM stage. This possibility is illustrated in Fig 5 in which the greater the increase in BF (with increasing venous return), the more HF (ie, parasympathetic nerve activity) is stimulated.…”

Relation between Sodium Intake and Blood Pressure during Sleep in Young Men.

“…In our detailed analysis of 24-h BP (26,27), we have shown that, whereas daytime BP changes markedly according to physical and mental activity, minimum sleep BP (base BP) is stable (10,26). We have reported that this BP could be the true basal BP that Smirk et al (28) had advocated.…”

“…We have reported that this BP could be the true basal BP that Smirk et al (28) had advocated. Because base BP is measured during deep sleep, at a time when the heart rate is low and stable, it is little affected by daytime activity (10,26,27,29). In addition to sodium intake, daytime BP is affected by a large number of other factors, including physical and mental activity.…”