Anticipation of sleep benefits heart

Short afternoon naps, or siestas, can reduce the risk of heart diseases, a team of researchers from John Moores University in Liverpool have found. According to Mohammad Zaregarizi and his colleagues, it is the anticipation period before the sleep that benefits our heart. These findings were first published in the Journal of Applied Physiology in July 2007.

Afternoon naps, no more than an hour, are practiced in many Mediterranean and Latin American countries like Spain and Argentina. These naps are believed to reduce the blood pressure, which in turn reduces strain on heart and eventually the risk of fatal heart attacks as well.

Zaregarizi and his colleagues compared napping with other daytime activities like standing and lying down without falling asleep. They enrolled a total of nine volunteers who attended the lab on three occasions, each session one hour long. They were allowed to sleep on one occasion, and stand still and lie down on the other two. At all sessions, blood pressure, heart rate, and forearm cutaneous vascular conductance - which determines dilation of blood vessels - were measured.

They observed the sleep session in three phases. The first phase lasted for five minutes of wakefulness, in which lights were still on. The second period extended from the moment lights were put out to the beginning of stage one sleep, in which some conscious awareness of the external environment is lost. The third phase extended from the second phase to the onset of stage two sleep, characterized by complete loss of conscious awareness of the external environment. The distinction of phases was made with polysomnography recordings.

Researchers found a significant drop in blood pressure during the sleep trial, but not during the lying down and standing trials. In addition, they noticed the changes only during the second phase of their observation. This means the anticipation of sleep benefits our heart more than the actual sleep does.

Next the researchers plan to study blood pressure variation during the waking portion of the afternoon nap to extend their understanding of its effects on the functioning of heart.

Written by Suvash Shrestha

Reviewed by Lisa Merolla

Published by Pooja Ghatalia

JYI publishes undergraduate research from the natural sciences, mathematics, engineering, and from some of the social sciences, such as psychology and the history of science.
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