Circadian blood pressure patterns in ambulatory hypertensive patients: effects of age.

Circadian blood pressure monitoring was performed in 50 untreated ambulatory hypertensive patients to study the effects of age on the pattern and variability of blood pressure and heart rate. Casual blood pressure, measured in the morning, was greater than the average of the blood pressures measured at 7.5 minute intervals for 24 hours (148 +/- 2/95 +/- 2 and 137 +/- 2/88 +/- 2 mm Hg, p less than 0.001). The correlation between casual systolic pressure and the 24 hour average was stronger (p less than 0.05) in younger (less than 55 years of age) patients (r = 0.69, n = 24, p less than 0.001) than in older patients (r = 0.42, n = 26, p less than 0.1). Similarly, diastolic pressures correlated more strongly (p less than 0.05) in younger patients (r = 0.71, p less than 0.001) than in older patients (r = 0.43, p less than 0.05). Variability of systolic pressure, defined as the standard deviation of all readings obtained during 24 hours, was greater than that of diastolic pressure (16.7 and 13.1 mm Hg, respectively, p less than 0.001). Moreover, the variability of systolic pressure was greater in older than in younger patients (18.1 and 15.2 mm Hg, respectively, p less than 0.01). The variability of diastolic pressure was slightly but not significantly greater in older patients (13.7 and 12.5 mm Hg, not significant). The circadian pattern of blood pressure, expressed as averages of readings obtained during consecutive 2 hour intervals, was similar in the two age groups. However, the level of systolic pressure was consistently higher (p less than 0.01) and that of both diastolic pressure and heart rate consistently lower (p less than 0.01) in older patients. Thus, ambulatory circadian blood pressure monitoring reveals significant changes in blood pressure levels and its variability with age; the casual blood pressure does not accurately reflect these changes. Longer periods of blood pressure monitoring are required for accurate assessment of the characteristics of hypertension in the aged.