Age-Related Alterations in the Circadian Pattern of Blood Pressure

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Abstract
The effect of age on the circadian pattern of arterial blood pressure was investigated in 12 healthy elderly male volunteers (64.0 ± 1.8 years of age) and in 12 young healthy men (24.0 ± 3.1 years of age). Ambulatory blood pressure (BP) was recorded every 10 min by indirect measurement during one 24-hour period. The averages and standard deviations of systolic BP throughout the 24-hour period were 116.8 ± 9.6 mm Hg in the elderly and 118.2 ± 8.7 mm Hg in the young. Those of heart rate were 65.3 ± 9.6 bpm in the elderly and 69.3 ± 7.4 bpm in the young. The most conspicuous finding in all subjects was the early morning rise in BP and heart rate, following the nocturnal fall during sleep. The arousal rise in BP was more prominent in the elderly (p < 0.01), while the arousal rise in heart rate was more prominent in the young (p < 0.01). The circadian pattern of BP in the elderly showed two major peaks. The highest peak was from 07.00 to 11.00 h. The second peak was from 17.00 to 21.00 h. A similar circadian profile was observed in pressure rate product (PRP). The 24-hour cosine functions fitted on the chronogram of systolic BP show a phase shift to the earlier clock time in the elderly (p < 0.01): acrophase, that is the crest time of the fitted cosine function, in the young 16.5 ± 1.2 h and in the elderly 12.9 ± 1.6 h. Not only BP monitoring but also ambulatory ECG monitoring and autonomic cardiovascular functions were examined. As a result, resting vagal cardiac activity (p < 0.05), baroreflex sensitivity (p < 0.10) and ß-receptor responsiveness (p < 0.05) were significantly depressed in the elderly. These alterations of autonomic regulatory functions appear to be related to the alteration on the circadian profiles of BP and PRP.

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