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Studies of astronauts' sleep indicate they average about six hours per day while in orbit, which is below the amount they receive on Earth. Although the reasons for this sleep loss are unknown, it is suspected that excitement, extended work schedules, environmental disturbances and microgravity are leading culprits.
"Whatever the cause, extensive ground-based research shows that chronically reduced sleep impairs thought processes and slows reaction times," said Dr. David Dinges, National Space Biomedical Research Institute's (NSBRI) Neurobehavioral and Psychosocial Factors Team Leader. "Mental mistakes and lapses of attention increase. Also, complex problem solving, learning and emotional reactions can be affected."
Dinges, also on the NSBRI's human performance team, hopes to find a solution to chronic sleep loss in space.
To help astronauts get the most benefit from sleep, Dinges wants to identify the ideal combination of one major, "anchor" sleep period combined with a short nap each day. He is focusing on daily naps because studies have shown greater recovery of sleep's benefits during the early hours of sleep. For this reason, dual sleep periods totaling four to six hours are being tested to determine if the combinations will produce the same benefits as a single eight-hour sleep period.
"We want to know if these anchor and nap sleep combinations will prevent the harmful effects of reduced sleep that occur when they don't take a nap," said Dinges, who is chief of the Division of Sleep and Chronobiology in the Department of Psychiatry at the University of Pennsylvania School of Medicine.
Eighteen combinations of anchor sleep and naps are being studied to establish the best way to reduce sleep debt.
The study involves putting diverse groups of healthy men and women into a suite of small rooms for two weeks to simulate space flight's low light, tight quarters and lack of social contact with the outside world. Participants undergo neurobehavioral performance testing and continuous monitoring of brain activity, sleep, body temperature, behavior and mood changes. Samples of key circadian and sleep-regulated regulatory hormones, such as melatonin, cortisol and human growth hormone, are taken to determine whether various sleep combinations adversely affect their secretions.
Using statistical modeling, test results will provide information on the most efficient sleep-wake schedules with the goal of minimizing cognitive and physiological deficits. The project also looks at whether age and gender affect results.
This research is relevant for space flight ground personnel who must work on round-the-clock schedules. Results will also have important implications for optimizing work-rest scheduling in safety-sensitive industries, such as transportation, military, public safety and health care. Findings could also benefit people suffering from pain, insomnia or other clinical illnesses that disrupt sleep.
"There is mounting evidence that the immune system and metabolic processes can be affected by the amount of sleep we obtain," Dinges said. "We are working with investigators at The Children's Hospital of Philadelphia, Harvard Medical School and the NSBRI Immunology, Infection and Hematology Team to study this further."
National Space Biomedical Research Institute. January 2002.
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