Effects of anticipation of a significant event on sleep during long-term isolation

Abstract

Introduction Modern theories suggest that chronic and acute stress is one of the predisposing factors of insomnia. Anticipation of a significant event also may cause sleep problems. Materials and methods ”Mars-520â” is an international project for simulating aspects of an interplanetary manned flight, organized by Institute for Bio-Medical Problems, RAS. Six healthy men from 27 to 38 years were isolated in the model of a spaceship for 520 days. Polysomnography during two consecutive nights were recorded 2 months before, during (4 times) and 2 weeks after the isolation. During confinement we studied sleep 40 days after the begining of the experiment, 2 weeks before and after simulation of Mars landing and 50 weeks before the end of the experiment. Statistics. First we transformed (log10 transformation) variables with significant deviation from a normal distribution. For comparison sleep parameters we used multiple regression with period of experiment as a dependent variable, subject and sequence of night as co-variances. If statistically significant difference was found, Tukey post hoc test was used for pair-wise comparison. Results During the isolation sleep efficiency and delta-latency decreased, while sleep latency increased mainly one and a half months before the end of the isolation. Pairwise comparison revealed significant differences between background and the last measure during isolation. Frequency of nights with low sleep efficiency significantly increased before important events for cosmonauts like simulation of Mars landing and the end of the confinement. Two weeks after landing simulation the amount of the nights with low sleep efficiency significantly decreased. Conclusion Anticipation of a significant event during long-term isolation might be a factor for sleep worsening and might result in sleep initiation problems in healthy men. Acknowledgement This research was supported by a grant from the RFH project – 110601052D°.