ABSENCE OF ENDOGENOUS CIRCADIAN RHYTHMICITY IN BLOOD-PRESSURE

Currently available evidence reveals a predominant role of exogenous ( so-called ''masking'') factors in the 24 h variation of blood pressure in humans. The existence of a (minor) endogenous circadian factor can not be excluded, however. This possibility was tested by applying the rigorous unmasking conditions of the constant-routine protocol, that i s, strict bed rest in a separate bedroom, total sleep deprivation, con stant ambient temperature and illumination, and hourly equicaloric foo d and liquid intake. Twenty-five normotensive young individuals were s ubjected to a 26 h constant-routine procedure while hourly measurement s were made of their blood pressure and heart rate. Repeated-measures analysis of variance failed to show a significant 24 h variation of bl ood pressure. The power of this test appeared satisfactorily high (>0. 95). Heart rate, however, exhibited a significant circadian pattern, w ith a range of 6.7 beats/min (10% of the 24 h mean value). Moreover, t he timing of the 24 h heart rate curves differed significantly between so-called morning (n = 10) and evening (n = 9) individuals. Mean peak values for the morning-types occurred at 11 AM, for the evening types nearly 6 h later. In conclusion, no evidence was found for the involv ement of a circadian oscillator in the regulation of blood pressure. ( C) 1998 American Journal of Hypertension, Ltd.