Effects of human thermophysiology and psychology in exposure to simulated microgravity

Background: Affected by the microgravity, astronauts will experience physiological discomfort in spaceflight, leading to an impaired ability of thermoregulation and deteriorating the mentality and operational performance of astronauts. It is significant to research on the thermophysiological and psychological phenomena in microgravity for the improvement of the astronauts' long-term comfort in orbit and out of the cabin. Objective: This study aims to explore the effects of microgravity on human thermophysiology and psychology, as well as the correlation between the two indexes, so as to provide a theoretical basis for the thermal control system and mental health protection in space suits and space stations. Methods: The sublingual temperature, local skin temperatures and anxiety-depression psychological indexes of 12 subjects in a stable thermal environment were monitored. The experimental period was 29 days, in which the first 7 days were for the adaptation and basic data collection, the following 15 days were for −6° head down bed rest (HDBR), and the last 7 days after getting up were for the recovery and physical examination. The thermophysiological and psychological indexes were measured on the 4th day before HDBR, the 1st, 5th, 9th, 13th day during HDBR and the 2nd day after HDBR. The temperatures were measured three times one day (morning, noon and evening). Results: The duration of HDBR had significant effects on the sublingual temperature (p = 0.017) and the weighted average skin temperature (p = 0.014), while the effect on anxiety is marginally significant (p = 0.065). Anxiety and depression scale scores are significantly correlated in simulated microgravity (p = 0.016), while no significant correlation is found between the sublingual temperature and anxiety-depression scale scores (p > 0.05), nor the weighted average skin temperature and anxiety-depression scale scores (p > 0.05). The back skin temperature and the anxiety score are significantly correlated in simulated microgravity (p = 0.012). Conclusions: The peak of anxiety and depression in the early stage of HDBR appeared on the 5th day. Thermophysiological and psychological adaptation occurred in the middle period, with values recovering to the initial levels in the later stage and after HDBR. This study could support the improvement of the thermal control system in space suits and space stations, and the protection of astronauts' mental health. A larger set of subjects and a longer experimental period could be considered in the future research, exploring more precise and complete principles of human thermophysiological and psychological changes in simulated microgravity.