CO2 exposure training is an important tool to educate astronauts about their potential acute CO2 symptoms. Wide interindividual and temporal variations were observed in symptoms reported during astronaut CO2 exposure training. Headache could not be relied on as a marker of acute exposure during testing since fewer than half the subjects reported it. Our results support periodic refresher training since symptoms may change over time. Further study is needed to determine the optimal interval of training to maximize symptom recognition and inform operational decisions.Law J, Young M, Alexander D, Mason SS, Wear ML, Méndez CM, Stanley D, Meyers Ryder V, Van Baalen M. Carbon dioxide physiological training at NASA. Aerosp Med Hum Perform. 2017; 88(10):897-902.

INTRODUCTION: Carbon monoxide (CO) is a toxic gas with potential for detriment to spaceflight operations. An analytical model was developed to investigate if a maximum CO contamination of 1 ppm in the oxygen (O2) supply reached dangerous levels during extravehicular activity (EVA). Occupational monitoring pre- and postsuited exposures provided supplementary data for review.METHODS: The analytical model estimated O2 and CO concentrations in the extravehicular mobility unit (EMU) based on O2 and CO flow rates into and out of the system. The model was based on 3 h of prebreathe at 15.2 psia, 8 h of EVA at 4.3 psia, and 1 h at 15.2 psia for suit doffing. The Coburn-Forster-Kane equation was used to calculate crewmember carboxyhemoglobin saturation (COHb%) as a function of time. Monitoring of hemoglobin CO saturation (Spco) with a CO-oximeter was conducted pre- and post-EVA during operations on the International Space Station and in ground-based analog environments.RESULTS: The model predicted a maximum PCO in the EMU of 0.061 mmHg and a maximum crewmember COHb% of 2.1%. Operational Spco measurements in mean ± SD during ground-based analog testing were 0.7% ± 1.8% pretest and 0.5% ± 1.5% posttest. Spco values on the ISS were 1.5% ± 0.7% pre-EVA and 1.1% ± 0.3% post-EVA.DISCUSSION: The model predicted that astronauts are not exposed to toxic levels of CO during EVA and operational measurements did not show significant differences between Spco levels between pre- and post-EVA.Makowski MS, Norcross JR, Alexander D, Sanders RW, Conkin J, Young M. Carbon monoxide levels in the extravehicular mobility unit by modeling and operational testing. Aerosp Med Hum Perform. 2019; 90(2):84–91.

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