Sleep in space as a new medical frontier: the challenge of preserving normal sleep in the abnormal environment of space missions

Abstract

Space agencies such as the National Aeronautics and Space Administration of the United States, the Russian Federal Space Agency, the European Space Agency, the China National Space Administration, the Japan Aerospace Exploration Agency, and Indian Space Research Organization, although differing in their local political agendas, have a common interest in promoting all applied sciences that may facilitate man’s adaptation to life beyond the earth. One of man’s most important adaptations has been the evolutionary development of sleep cycles in response to the 24 hour rotation of the earth. Less well understood has been man’s biological response to gravity. Before humans ventured into space, many questioned whether sleep was possible at all in microgravity environments. It is now known that, in fact, space travelers can sleep once they leave the pull of the earth’s gravity, but that the sleep they do get is not completely refreshing and that the associated sleep disturbances can be elaborate and variable. According to astronauts’ subjective reports, the duration of sleep is shorter than that on earth and there is an increased incidence of disturbed sleep. Objective sleep recordings carried out during various missions including the Skylab missions, space shuttle missions, and Mir missions all support the conclusion that, compared to sleep on earth, the duration in human sleep in space is shorter, averaging about six hours. In the new frontier of space exploration, one of the great practical problems to be solved relates to how man can preserve “normal” sleep in a very abnormal environment. The challenge of managing fatigue and sleep loss during space mission has critical importance for the mental efficiency and safety of the crew and ultimately for the success of the mission itself. Numerous "earthly" examples now show that crew fatigue on ships, trucks, and long-haul jetliners can lead to inadequate performance and sometimes fatal consequences, a reality which has caused many space agencies to take the issue of sleep seriously.

Expedition Cognition: A Review and Prospective of Subterranean Neuroscience With Spaceflight Applications

“…The degree to which spaceflight sleep problems are caused by altered physiology due to the effects of microgravity itself or other factors such as isolation and confinement, noise, changes in physical activity, long or unusual sleep-wake and crew shift-work schedule, over-excitation, demographics, rapid succession of light and dark exposure, and ambient temperature is not yet known (Gundel et al, 1997 ; Pandi-Perumal and Gonfalone, 2016 ). However, results from space analogs also report significant changes in sleep patterns during Antarctic overwintering (Steinach et al, 2016 ) and during extended confined isolation (Basner et al, 2013 ), respectively, suggesting that sleep disturbance can be usefully studied in space analog conditions.…”

On-orbit sleep problems of astronauts and countermeasures

“…Good sleep generally includes sufficient sleep duration and good sleep quality. Unfortunately, evidence has consistently shown that disrupted sleep is a very common and important problem among astronauts [ 1 , 2 ]. In human spaceflight, sleep duration and sleep quality of astronauts were adversely affected by combined special factors including microgravity, isolation, monotonous repetition, high vigilance workload and so on.…”

“…On the basis of several times of short-term manned spaceflight practices, China has attached more and more importance to on-orbit sleep problems of astronauts and considered it as one of the key factors for keeping human performance capabilities in medium and long-term spaceflight [ 3 ]. In recent years, researchers focus on the effects of space flight on sleep and the countermeasures which gradually become a new frontier of space medicine [ 1 – 4 ]. In this article, the research progress in this field was reviewed and analyzed to provide reference for the study of sleep medicine in medium and long-term human spaceflights, so as the circumstances for similar extreme environmental practitioners in China.…”

Negative correlation between gestation and sleep durations in mammals

“…As a result of this adaptation to a "truncated" environment, their REM sleep is reduced. 37,38 Experiments submitting rats to an environment of hypergravity are planned, and it is expected that their REM sleep will be longer.…”