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Anticipation of An Afternoon Nap Can Lower Blood Pressure

By Bob Ewing     Oct 15, 2007 in Health
To nap or not to nap, that is the question. A research team has conducted a study that indicates that the expectation of a nap and the time just before falling asleep may be where the benefits lies.
Is there any benefit to taking an afternoon nap? If there is, is it the nap itself or the anticipation of the nap that brings the benefit? A team of researchers in the United Kingdom have determined that the time just before you fall asleep is where beneficial cardiovascular changes take place.
This finding is part of a larger study that is Acute Changes in Cardiovascular Function During the Onset Period of Daytime Sleep: Comparison to Lying Awake and Standing, found in the online edition of the Journal of Applied Physiology, published by The American Physiological Society.
Mohammad Zaregarizi, Ben Edwards, Keith George, Yvonne Harrison, Helen Jones and Greg Atkinson, of the Liverpool John Moores University in Liverpool, U.K. undertook the study.
The nap is a regular activity in many Mediterranean and Latin American countries such as Spain and Argentina. The average nap is short, no longer than an hour in length and usually taken in the afternoon.
Previous studies have found that this practice may slightly increase the risk of heart attack, however, more recent research and better controlled studies have shown an inverse relationship between siesta taking and fatal heart attacks.
In Greece a recent epidemiological study of 23,000 people showed that the people who regularly took siestas had a 37% reduction in coronary mortality compared to those who never nap, while individuals who occasionally napped in the afternoon had a reduction of 12%.
So how do afternoon naps affect cardiovascular function? Changes in blood pressure may be one reason. Blood pressure and heart rate decrease while we sleep. It has been suggested that the lower blood pressure reduces strain on the heart and decreases the risk of a fatal heart attack.
Previous studies, for the most part, have focused on cardiovascular behavior in nighttime sleeping. The new study provides a detailed description of changes in cardiovascular function of daytime sleep in healthy individuals and compares napping with other daytime activities such as standing and lying down without going to sleep.
The team tested nine healthy volunteers (eight men, one woman) all of whom did not routinely take afternoon naps. Each volunteer attended the university laboratory on three separate afternoons after sleeping four hours the night before.
Each had to wear equipment that checked blood pressure, heart rate, and forearm cutaneous vascular conductance (which determines dilation of blood vessels).
For one afternoon session, the volunteer spent an hour resting, lying face-up in bed; in another session, the volunteer spent an hour relaxed, but standing. While in a third session the volunteer was allowed an hour to sleep, lying face-up. It was during the sleep stage that the researchers measured the volunteer’s different stages of sleep.
The session in which the volunteer was allowed to fall asleep was delineated into three phases:
• Phase 1: A five-minute period of relaxed wakefulness before lights were turned off (volunteers had been lying on the bed for a minimum of 15 minutes before this phase)
• Phase 2: The period between “lights out” and the onset of Stage 1 sleep (loss of some conscious awareness of the external environment)
• Phase 3: The period between the Stage 1 and the onset of Stage 2 sleep (conscious awareness of the external environment disappears)
It was only during the sleep trail that the researchers found a significant drop in blood pressure not during the resting or standing trials. What is significant here is that this drop in blood pressure occurred mostly after lights out, just before the volunteer fell asleep.
It is this reduction in blood pressure that may offer one explanation for the lower cardiovascular mortality that some studies have found among people who habitually take siestas.
Some studies of nocturnal sleep have shown that blood pressure rises when we awake and that more cardiac deaths occur in the mornings. For this reason the research team will look at blood pressure during the waking portion of the afternoon nap in order to determine if this period may also pose an increased danger of coronary mortality.
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