Repeated assessment of the endogenous 24-hour profile of blood pressure under constant routine

The impact of environmental and behavioral factors on the 24-h profile of b lood pressure (BP) has been well established. Various attempts have been ma de to control these exogenous factors, in order to investigate a possible e ndogenous circadian variation of BP. Recently, we reported the results of t he first environmentally and behaviorally controlled laboratory study with 24-h recordings of BP and heart rate (HR) during maintained wakefulness. In this constant-routine study, a pronounced endogenous circadian rhythm of H R was found, but circadian variation of BP was absent. This result suggeste d that the circadian rhythm of BP observed in earlier controlled studies, w ith sleep allowed, was evoked by the sleep-wake cycle as opposed to the end ogenous circadian pacemaker. In order to verify our previous finding during maintained wakefulness, we repealed the experiment five times with six nor motensive, healthy young subjects. Statistical analyses of the hourly measu rements of BP and HR confirmed the replicable presence of an endogenous cir cadian rhythm of HR. as well as the consistent absence of an endogenous cir cadian variation of BP. Thus, this study provided additional evidence that the 24-h profile of BP-as observed under normal circumstances-is the sole r esult of environmental and behavioral factors such as the occurrence of sle ep, and has no endogenous circadian component.