Blood pressure variability in health, hypertension and autonomic failure.

24h intra-arterial pressure monitoring was used to examine blood pressure variability in 5 normal volunteers, 137 subjects with suspected or established essential hypertension and 9 subjects with autonomic failure. Subjects with autonomic failure showed increased short-term blood pressure variability while active but reduced values at rest. Heart rate variability was low at all times. 24h recordings were reduced to hourly mean values and two indices of variability derived - day-night difference and average hourly change. For blood pressure, subjects with autonomic failure showed negative values of the former but high values of the latter; both indices of heart rate variability were low. In the remaining group, the relationship of these indices to constitutional factors, mean blood pressure and indices of physical activity during the study was explored. Day-night difference in systolic pressure was negatively correlated with mean pressure and average hourly change positively related to age. No other relationship was significant.