Changes in the pattern of sleep disturbances in healthy subjects under 21-day antiorthostatic hypokinesia

Background. Antiorthostatic hypokinesia (ANOH) reproduces some of the effects of weightlessness on the human body and is used to study adaptation to space flight conditions. It is known that ANOH affects nighttime sleep, but there is no information in the literature on the sequence of occurrence of sleep disorders in ANOH.

The aim of the research was to study the dynamics of subjective changes in assessing sleep quality under conditions of antiorthostatic hypokinesia.

Materials and methods. Six healthy male volunteers (age from 26 to 34  years) participated in the experiment with 21-day ANOH. They were on a medical bed with a body inclination angle relative to the horizon of –6° for 21 days. To assess sleep quality, a structured questionnaire was used that assessed sleep duration, rate of falling asleep, night awakenings, the presence of daytime sleepiness, and daytime falling asleep.

Results. Based on the assessment of the dynamics of the sleep efficiency index (SEI), three stages of adaptation were identified. At the stage of acute adaptation (the first 3 days), there is a decrease in SEI from 96.4 to 91.3 (p < 0.01), a statistically significant prolongation of falling asleep from 17.6 to 33.6  minutes (p  <  0.01), an increase duration of night awakenings up to 17.4 minutes, increase in daytime sleepiness by 11 %. In the next 3 days (the “recovery” stage), there is a statistically significant increase in SEI compared to the 1st stage to 94.7 (p < 0.01), but it remains statistically significantly lower than the background values (p < 0.004). The number of complaints about daytime sleepiness increases (up to 42  %), evening bedtime shifts later by 26 minutes. At the 3rd stage (the remaining nights) there is a relative stabilization of the sleep-wake cycle.

Conclusion. Under conditions of 21-day ANOH, a gradual change in the pattern of sleep disturbances occurs. The most negative changes in terms of subjective assessment were noted in the first three days. Then there is an improvement in falling asleep, a decrease in night awakenings, combined with an increase in daytime sleepiness and the formation of a schedule with a later bedtime.

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