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 cannot be excluded, however. This possibility was tested by applying the rigorous unmasking conditions of the constant-routine protocol, that is, strict bed rest in a separate bedroom, total sleep deprivation, constant ambient temperature and illumination, and hourly equicaloric food and liquid intake. Twenty-five normotensive young individuals were subjected to a 26 h constant-routine procedure while hourly measurements were made of their blood pressure and heart rate. Repeated-measures analysis of variance failed to show a significant 24 h variation of blood pressure. The power of this test appeared satisfactorily high (>0.95). Heart rate, however, exhibited a significant circadian pattern, with a range of 6.7 beats/min (10% of the 24 h mean value). Moreover, the 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 involvement of a circadian oscillator in the regulation of blood pressure.
Kerkhof
G A
GA
Department of Physiology, University of Leiden, The Netherlands. kerkhof@rullf2.leidenuniv.nl
Van Dongen
H P
HP
Bobbert
A C
AC
D000328:Adult; D001510:Bed Rest; D001794:Blood Pressure / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D003971:Diastole; D004780:Environment, Controlled; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D013599:Systole; D014851:Wakefulness / Q000502:physiology