Changes in the Basal Metabolic Rate of the Crew under Conditions of 8-Month Isolation in a Hermetic Object with a Moderately Hypercapnic Artificial Gas Environment: Report 1

Within the framework of the SIRIUS international project, a study of the basal metabolism of a gender-mixed crew in a sealed object with a moderately high content of carbon dioxide in an artificial atmosphere was conducted. Using mathematical methods, we estimated the basal metabolic rate (BMR) of a crew of five people (three men and two women) at rest for 240 days of isolation when simulating a flight to the Moon in the SIRIUS-21 experiment. The period of isolation lasted from November 4, 2021 to July 3, 2022. BMR studies were performed twice in the background (days –38 to –35 and –9 to –6), seven times during the isolation period (days 23–25, 50–52, 84–86, 110–112, 154–156, 181–183, and 222–224), and twice during the aftereffect period (days +1–2 and +8–9). It was found that the basal metabolism in isolation decreased by an average of 6 kcal/kg of body weight per day compared with natural environmental conditions. The crew was isolated from the effects of seasonal lighting changes in a sealed facility, the Ground-Based Medical and Technical Facility (NEK) of the State Scientific Center of the Russian Federation, Institute of Biomedical Problems, Russian Academy of Sciences, which does not have portholes, and where artificial lighting was created without seasonal changes. Inside the NEK, the comfort temperature was constantly maintained at +21–23°C and an artificial gas environment was formed, in which the oxygen content was maintained at 21%, carbon dioxide no more than 0.35%. In conditions of isolation from the action of these geophysical environmental factors, seasonal fluctuations in basal metabolism with a wave span of an average of 4 kcal/kg of body weight per day were detected: in the spring calendar season, the level of basal metabolism increased relative to the winter season. Seasonal local maximums and minimums of the basal metabolism level for 2 calendar seasons (winter 2021/2022 and in spring 2022) were determined for each of the volunteers. The results in this work can be applied in the field of space physiology to clarify the calculated oxygen reserves and caloric content of the crew’s rations for a long-term space mission, as well as in the design and programming of life support systems and thermal management systems for inhabited hermetic objects.