Twenty-Four-Hour Blood Pressure Control: An Intraarterial Review

Intraarterial blood pressure monitoring has shown the circadian rhythm of blood pressure control. Blood pressures tend to be highest in the morning before falling gradually during the day to a nadir at 3:00 a.m. There is a slight rise in the late afternoon that may correspond to patients' attendance at hospital for calibration of the equipment. There is a small rise in the blood pressure before awakening, and after arousal there is a rise in blood pressure to the peak level of the morning. In this article, we examine the effect of a variety of antihypertensive agents on this rhythm. In general, β-adrenoceptor blockers appear to have less effect on nocturnal blood pressure and surge in pressure after arousal, while vasodilators, particularly α-adrenoceptor blockers, have a pronounced effect. These findings indicate that the rise in blood pressure before awakening and the rapid rise upon arousal appear to be due to increased α-adrenoceptor activity.