Postural effects on the circadian rhythm of blood pressure and heart rate in young and elderly subjects.

This investigation compares the effects of changes in activity-rest patterns on the 24-hr rhythms of blood pressure and heart rate in elderly and young subjects. Blood pressure and heart rate were monitored by means of noninvasive, automatic, quasiportable recording equipment. The subjects either rested both diurnally and nocturnally or were active diurnally and rested nocturnally. Time-qualified data were analyzed for circadian rhythmicity by means of the cosinor procedure. In both activity-rest patterns, elderly subjects showed a dissociation between circadian rhythms of blood pressure and heart rate due to a peculiar shift of acrophases. Because of the particular timing of the acrophase, elderly subjects differed from young individuals in the overall adaptation of the blood pressure and heart rate 24-hr patterns to upright posture and physical activity. Of particular interest is the reduced amplitude in the circadian rhythm of blood pressure, which might contribute to the compromised orthostatic tolerance of older people.