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University Of Pittsburgh Researchers Find Potential Sleep Problems Await Astronauts On Long Missions

PITTSBURGH, November 21, 2001 Astronauts traveling to distant places such as Mars may find themselves suffering from sleep problems as their missions progress, say scientists at the University of Pittsburgh School of Medicine in a report to be published in the December issue of Psychosomatic Medicine.

The researchers, led by Timothy H. Monk, D.Sc., Ph.D., professor of Western Psychiatric Institute and Clinic at the University of Pittsburgh School of Medicine, found that the endogenous circadian pacemaker (ECP), which is the part of the brain controlling the body’s cycle of sleep, wakefulness, alertness, temperature, and brain chemistry, is able to maintain its 24-hour rhythm for about 90 days once removed from the natural time cues on Earth. After that time, the influence of the ECP appears to diminish significantly and the quantity and quality of sleep drops.

“Man’s ability to leave Earth and travel in space raises the question of whether the human endogenous circadian pacemaker (ECP), which evolved on a planet with a 24-hour rotation, would still function well when removed from all of the natural time cues of Earth,” said Dr. Monk. “Our study shows that human kind may need to find ways to trick the ECP into maintaining a strong 24-hour cycle if we are to succeed on longer missions.”

According to Dr. Monk, studies of animals orbiting in microgravity, the weightlessness astronauts experience while in orbit, have suggested that mechanisms which keep the ECP “on-track”, such as day and night, might be weakened in space. With funding from the National Aeronautic and Space Administration (NASA), and cooperation from American astronaut Jerry M. Linenger, M.P.H., Ph.D., who is a co-author of the study, the researchers set out to determine how Dr. Linenger’s ECP would change as the mission progressed and how those changes would impact his sleep, alertness and performance.

Dr. Linenger lived aboard Russian Space Station Mir for nearly five months, from January to May of 1997. The mission was an eventful one with a fire aboard, coolant leaks and a near collision. He has written a book about the mission titled “Off the Planet: Surviving Five Perilous Months Aboard the Space Station Mir.” While aboard Mir, Dr. Linenger recorded data on himself from three measurement blocks, each almost two weeks in duration. Block one consisted of days 37 to 50; block two, days 79 to 91; and block three, days 110 to 122. Dr. Linenger habitually went to bed and arose at fairly regular times (11:25 p.m. to 6:06 a.m.). During each measurement block Dr. Linenger was required to measure his oral temperature and rate his subjective alertness five times per day, recording his results on a laptop computer.

During each “morning” of a measurement block, within one hour of waking, Dr. Linenger completed a computer-based version of the Pittsburgh Sleep Diary, which yields measures of the times of bedtime and waking, the estimated duration of unwanted wakefulness and the amount and rated quality of the sleep obtained the preceding “night.”

Over the course of the mission the data showed an apparent “flattening” in the time-of-day function of Dr. Linenger’s body temperature and alertness, indicating weakened ECP influence. These findings coincided with his subjective impressions. In block three, Dr. Linenger often forced himself to go to bed “by the clock” without feeling sleepy as a deliberate strategy to keep a rigid routine and to lessen the feeling of being dissociated from 24-hour time.

“Because one of the major functions of the ECP is to prepare a person for a restful night of sleep, we were particularly concerned with what would happen to the sleep variables during block three,” said Dr. Monk. “We found a drop in the estimated amount of sleep Dr. Linenger got during that block, resulting mostly from an increase in the number of times he woke up during the night. This is the sort of sleep disruption we would expect when the ECP is not doing its job properly.”

“The bottom line is we now know that the human body clock may lose its influence once we leave the planet for extended periods,” said Dr. Monk. “We still have to determine if and how longer missions, such as to Mars, could be jeopardized by performance problems associated with poor sleep and ECP disruption. More research is needed with a greater number of subjects and better measures of ECP functioning.”

Research was supported by NASA.

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