Sunday, January 30, 2005

ClockNews #19: It's slower than you thought

Body clock is slow to adjust

Resetting the body’s biological clock to adjust to
dramatic time changes may take more tinkering than once thought, researchers
have found.Scientists at the University of Pittsburgh found that the common
practice of gradually moving bedtime up or back a bit at a time before an
overseas trip to help reduce the impact of jet lag does work, but only to a
certain point.The study is part of an ongoing project to come up with the best
way to help astronauts prepare their sleep habits for space travel, but the
findings may help anyone who has to deal with time or schedule changes."When we
have to change our sleep schedule, we often wonder if we should make the change
all at once or more gradually over several days or weeks. This research has the
eventual aim of helping us make that decision in the best way possible," said
Dr. Timothy Monk, a professor of psychiatry at Pitt’s medical school.Keeping
sleep-wake cycles straight is particularly hard for people living in space for
long periods, cut off from the natural cues on Earth. Like most animals, humans
have a biological clock in our head that’s able to keep time, getting us ready
to sleep at night and wakefulness during the day using rhythms with a period of
about 24 hours, called the circadian rhythms.But in orbit, the sunrise-sunset
cycle runs for just 90 minutes, and after being away from the natural 24-hour
cycle for several months, the biological clock starts to be thrown off balance,
with sleep and wakeful alertness suffering.In addition, astronauts often have to
be awake and alert at off-times to carry out experiments or vehicle maneuvers.
NASA has tried to meet those needs with a long-standing set of guidelines that
specify how much an astronaut’s bedtime can change from one day to the next,
generally favoring a "trickling in" approach of delaying sleep by up to two
hours when possible."The thought was that mission schedulers could trickle in a
series of two-hour phase delays without incurring any negative consequences as
far as sleep quality and alertness," Monk said. "However, based on the findings
from our experiment, that assumption might be quite wrong."In their experiment,
which was described in the December issue of the journal Aviation, Space and
Environmental Medicine, the researchers followedvolunteers who spent 16 days on
a "mission" in a time isolation facility at Pitt. They went through a series of
nine repeated two-hour delays in bedtime.The effect on circadian rhythms was
measured through tests for alertness, mood and core body temperature. At the
same time, sleep was monitored to assess duration and quality.Over the course of
the study, Monk’s team found that the circadian clock did adjust itself, but
only by about one hour a night, rather than the two hours expected under NASA’s
guidelines.As a result, the subjects eventually went through a massive
flattening of their natural sleep-wake rhythm, which led to significant
disruptions in sleep and lowered alertness when they were awake.The team is now
moving ahead with tests of other sleep cycle adjustments to see how subjects
respond. "There is always some cost to performing tasks when we expect to be
asleep, but by the end of our experiments, we should be able to tell which
approach - gradual delays, gradual advances or changes all at once - will lead
to the least disruption of an astronaut’s sleep and alertness," Monk


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