Characterization of metabolic changes and adaptive remodeling during a hypobaric hypoxic exploration atmosphere environment.

Introduction: The International Space Station maintains normoxic atmospheric conditions of 14.7 psia (101 kPa) and 21% oxygen. Astronauts don spacesuits to conduct extravehicular activities (EVAs), which operate at a reduced pressure of 4.3 psia (29.6 kPa), and a hyperoxic atmosphere of 100% oxygen. The reduction in pressure presents a risk of decompression sickness and is mitigated by a several hour denitrogenation (aka, prebreathe) protocol. To reduce the time required for prebreathe, future lunar and planetary exploration habitats and vehicles are expected to maintain a hypobaric, mildly hypoxic habitable environment in order to facilitate faster transitions to hypobaric hyperoxic EVAs. Among other things, hypoxic environments can influence oxidative stress and alter glucose metabolism, or other adaptive remodeling. Methods: Three 11-day chamber study missions (n=8/mission) were conducted to characterize the effects of alternating a mildly hypoxic living environment [8.2-9.6 psia (56.5 - 66.2 kPa)/28.5-34% oxygen] with hyperoxic EVAs [4.3 psia (29.6 kPa)/85-95% oxygen]. Fasting blood and 24-h urine samples were collected before the mission, and then again before and after EVAs on mission days (MD) 3 and 7, and a final collection on MD10. Results: Significant fluctuations of iron, amino acid, and glucose metabolism, along with changes in adaptive responses including some oxidative stress were observed before and after hyperoxic EVA simulations. Discussion: Based on these findings, it is evident that the effects of alternating hypoxia and hyperoxia may alter metabolism and physiology during exploration-class space missions.