Effects of carbon dioxide on physical and cognitive performance in a simulated spacesuit contingency scenario

Crewmembers on future Lunar and Mars surface missions will perform numerous surface exploration extravehicular activities (EVAs). NASA standards dictate a nominal upper limit to the inspired partial pressure of CO₂ (P_ICO₂) of 15 mmHg in spacesuits; however, there is no suited P_ICO₂ standard for emergency or contingency EVA scenarios. A laboratory-based study was conducted to characterize physical and cognitive performance, and self-reported symptomology during a simulated emergency one-hour EVA return to habitat scenario while being exposed to different P_ICO₂ levels. Fifteen healthy subjects (12 M/3 F) underwent 7 testing conditions (P_ICO₂ of 0, 5, 10, 15, 20, 25, and 30 mmHg) using a single-blinded, repeated-measures, counterbalanced design. All subjects completed the simulated contingency EVA scenario at all P_ICO₂ levels. Although statistically detectable dose-responses were observed in several variables, these changes did not reach levels associated with clinically or operationally relevant impairment during the one-hour exposures up to 30 mmHg P_ICO₂.