EMBARGOED
FOR RELEASE UNTIL
October 15, 2007
APS Contact
Christine Guilfoy
Office:
(301) 634-7253
cguilfoy@the-aps.org
www.The-APS.org
Expecting an Afternoon Nap Can
Reduce Blood Pressure
The
pre-sleep period of a nap shows a significant change in cardiovascular
function
BETHESDA, Md. — (Oct. 15, 2007) Where does the benefit
lie in an afternoon nap? Is it in the nap itself--or in the anticipation of
taking a snooze? Researchers in the United Kingdom have found that the time
just before you fall asleep is where beneficial cardiovascular changes take
place.
This finding is part of a study entitled 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. The study was conducted by Mohammad Zaregarizi,
Ben Edwards, Keith George, Yvonne Harrison, Helen Jones and Greg Atkinson,
of the Liverpool John Moores University in Liverpool, U.K.
The Afternoon Nap
Afternoon naps, or siestas, are practiced in many
Mediterranean and Latin American countries such as Spain and Argentina. They
are typically short naps or rest periods of no more than an hour that are
taken in the afternoon.
While earlier studies on siestas have found that this
practice may slightly increase the risk of heart attack, newer and more
controlled studies have shown an inverse relationship between siesta taking
and fatal heart attacks. In a recent epidemiological study of 23,000 people
in Greece, those who regularly took siestas showed 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%.
Why do afternoon naps affect cardiovascular function?
One reason could be changes in blood pressure. At night, our blood pressure
and heart rate decreases as we sleep. Some researchers hypothesize that the
lower blood pressure reduces strain on the heart and decreases the risk of a
fatal heart attack.
Most studies have focused on cardiovascular behavior in
nighttime sleeping. This study provides a detailed description of changes in
cardiovascular function of daytime sleep in healthy individuals, comparing
napping with other daytime activities such as standing and lying down
without going to sleep.
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 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)
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.
What’s 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. On the other hand, some studies of
nocturnal sleep have shown that blood pressure rises when we awake and that
more cardiac deaths occur in the mornings. So the John Moores team will next
look at blood pressure during the waking portion of the afternoon nap to see
if this period may also pose an increased danger of coronary mortality.
For an audio version of this release, including
portions of an interview with the principal author, Professor Greg Atkinson,
please go to
www.lifelines.tv.
To schedule an interview with the author, please
contact
Christine Guilfoy at
cguilfoy@the-aps.org or call (301) 634-7253.
Physiology is the study of how molecules, cells,
tissues and organs function to create health or disease.
The American Physiological Society (www.The-APS.org)
has been an integral part of this scientific discovery process since it was
established in 1887.
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