Involvement of the baroreceptor reflexes in the changes in blood pressure with sleep and mental arousal.

We have measured baroreflex sensitivity and blood pressure in 13 subjects during sleep and three stages of progressive mental arousal after waking. Baroreflex sensitivity was measured by correlating the increase in pulse interval with the increase in systolic pressure produced by an intravenous injection of 80 micrograms of phenylephrine. Blood pressure was measured directly from the brachial artery. During sleep, blood pressure fell and baroreflex sensitivity increased; with increasing mental arousal, blood pressure rose and baroreflex sensitivity decreased. These results suggest that baroreflex activity may be involved in the medium-term regulation of blood pressure during the day and night in addition to its recognized role in buffering acute changes in blood pressure.