Impact of 60-day head-down tilt bed rest simulating microgravity on sleep and the potential benefit of sensorimotor training

Kurzfassung

Introduction: Sleep and recovery are major concerns during long-duration spaceflight. Astronauts tend to sleep less than on Earth, and use sleep medication more frequently, potentially contributing to impaired cognitive performance and an increased risk of operational errors. Methods: 23 participants (11 female, 12 male participants; mean age (standard error): 32.26 (1.40) years; mean body mass index: 22.24 (0.54) kg/m2) completed 15 days of baseline assessment, 60 days of -6° head-down tilt (HDT) bed rest, and 14 days of recovery, with an 8-h nightly sleep opportunity. HDT bed rest is a well-established analog model of microgravity-induced physiological changes. Data were recorded as part of the NASA/DLR "Sensorimotor Countermeasures Study". This analysis assessed the effects on sleep outcomes using polysomnography and sleep questionnaires. Results: During the first HDT night, total wake time increased by 33.42 min (p < 0.001) and wake after sleep onset increased by 42.04 min (p < 0.001) compared to baseline, accompanied by an 18.81 min (p = 0.006) decrease in rapid eye movement (REM) sleep. Total sleep time decreased by 40.15 min (p = 0.007) and sleep efficiency by 8.41 percentage points (p = 0.01). By the eighth night in HDT, most sleep parameters no longer differed significantly from baseline. Subjective sleep parameters remained unchanged throughout. Significant sex differences were identified in REM sleep and arousal frequency. Men exhibited less REM sleep than women during the first HDT night and more arousals over the course of the study. The countermeasures did not significantly affect sleep parameters, although small group sizes may have limited statistical power. Discussion: In contrast to previous HDT studies reporting persistent sleep impairment, objective sleep disturbances were largely restricted to the first HDT night. Larger studies are needed to assess the reproducibility of this adaptation, the observed sex differences, and the effects of the countermeasures.