Ultradian Oscillations in Human Blood Pressure: Effects of Age
We postulated that normative aging is a progressive loss of dynamic stability that might manifest itself through spectral changes in cardiovascular processes. Using ambulatory monitoring we obtained 24 h time-series data on systolic pressure, diastolic pressure and heart rate in 13 subjects younger than 50 years and 25 subjects age 50 or older. All were in good health without history of cardiovascular disease. The two groups did not differ in heart rate or diastolic pressure with respect to means, variances, or power spectral profiles; but they differed significantly in systolic pressures. Overall, the old had higher 24 h mean systolic pressure than the young. In 15 of the old systolic pressures during sleep were at the same levels as those of the young during sleep, but in 10 it was approximately 25 mm Hg higher. We therefore subcategorized the old as sleep-normotensive systolic old (NTO) or sleep-elevated systolic old (ESO). In both subgroups systolic pressure during wakefulness was the same and averaged 15–20 mm Hg higher than that for the young. Although systolic 24 h variance was higher overall in the old than in the young, the NTO group provided most of that increase; their systolic pressure wa3 low during sleep but elevated during wakefulness. Power spectral profiles showed that the variance of the systolic pressure spectrum of the young was evenly distributed over ultradian period ranges. In contrast, both subgroups of the old showed concentration of systolic variance at periods of approximately 40 min and 3 h. We concluded that with respect to systolic pressure dynamics, the two subgroups of old may represent different physiological states: those normotensive during sleep but with 3lightly elevated pressures during wakefulness may reveal a normative aging process; those with elevated systolic pressures during sleep as well as during the day may represent early stages of impending isolated systolic hypertension. In both cases the appearance of ultradian rhythms with periods of about 40 min and 3 h may be a manifestation of intrinsic aging, independent of disease.
KeywordsHeart Rate Systolic Pressure Diastolic Pressure Systolic Hypertension Ambulatory Monitoring
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