Nap versus Conscious Rest
The researchers tested nine healthy volunteers (eight men, one woman) who did not routinely take afternoon naps. The volunteers attended the university laboratory on three separate afternoons after sleeping four hours the night before. The volunteers wore equipment that checked blood pressure, heart rate, and forearm cutaneous vascular conductance (which determines dilation of blood vessels).
During one afternoon session, the volunteer spent an hour resting, lying face-up in bed. During another session, the volunteer spent an hour relaxed, but standing. And in one session, the volunteer was allowed an hour to sleep, lying face-up. During the sleep stage, the researchers measured the volunteers different stages of sleep.
The session in which the volunteer was allowed to fall asleep was delineated into three phases:
Changes Found Only in Pre-Sleep
Researchers found a significant drop in blood pressure during the sleep trial, but not during the resting or standing trials. Whats more, this drop in blood pressure occurred mostly after lights out, just before the volunteer fell asleep.
This reduction in blood pressure may be one explanation for the lower cardiovascular mortality that some studies have found among people who habitually take siestas.
|Contact: Christine Guilfoy|
American Physiological Society