BACKGROUND: NASA has been making efforts to assess the carbon dioxide (CO₂) washout capability of spacesuits using a standard CO₂ sampling protocol. This study established the methodology for determining the partial pressure of inspired CO₂ (PIco₂) in a pressurized spacesuit. We applied the methodology to characterize PIco₂ for the extravehicular mobility unit (EMU). METHODS: We suggested an automated and mathematical algorithm to find the end-tidal CO₂ and the end of inspiration. We provided objective and standardized guidelines to identify acceptable breath traces, which are essential to accurate and reproducible calculation of the in-suit inhaled and exhaled partial pressure of CO₂ (Pco₂). The mouth guard-based method for measurement of inhaled and exhaled dry-gas Pco₂ was described. We calculated all individual concentrations of PIco₂ inhaled by 19 healthy subjects classified into 3 fitness groups. The transcutaneous Pco₂ was monitored as a secondary measure to validate washout performance. RESULTS: Mean and standard deviation values for the data collection performance and the CO₂ metrics were presented (e.g., minimum time weighted average Pco₂ at suited workloads of resting, 1000, 2000, and 3000 (BTU h1) were 4.75 1.03, 8.09 1.39, 11.39 1.26, and 14.36 1.29 (mmHg s1). All CO₂ metrics had a statistically significant association and all positive slopes with increasing metabolic rate. No significant differences in CO₂ metrics were found between the three fitness groups.DISCUSSION: A standardized and automated methodology to calculate PIco₂ exposure level is presented and applied to characterize CO₂ washout in the EMU. The EMU has been operated successfully in over 400 extravehicular activities (EVAs) and is considered to provide acceptable CO₂ washout performance. Results provide a basis for establishing verifiable Pco₂ requirements for current and future EVA spacesuits.Kim KJ, Bekdash OS, Norcross JR, Conkin J, Garbino A, Fricker J, Young M, Abercromby AFJ. The partial pressure of inspired carbon dioxide exposure levels in the extravehicular mobility unit. Aerosp Med Hum Perform. 2020; 91(12):923931.
BACKGROUND: NASA has been making efforts to assess the carbon dioxide (CO₂) washout capability of spacesuits using a standard CO₂ sampling protocol. This study established the methodology for determining the partial pressure of inspired CO₂ (PIco₂) in a pressurized spacesuit. We applied the methodology to characterize PIco₂ for the extravehicular mobility unit (EMU). METHODS: We suggested an automated and mathematical algorithm to find the end-tidal CO₂ and the end of inspiration. We provided objective and standardized guidelines to identify acceptable breath traces, which are essential to accurate and reproducible calculation of the in-suit inhaled and exhaled partial pressure of CO₂ (Pco₂). The mouth guard-based method for measurement of inhaled and exhaled dry-gas Pco₂ was described. We calculated all individual concentrations of PIco₂ inhaled by 19 healthy subjects classified into 3 fitness groups. The transcutaneous Pco₂ was monitored as a secondary measure to validate washout performance. RESULTS: Mean and standard deviation values for the data collection performance and the CO₂ metrics were presented (e.g., minimum time weighted average Pco₂ at suited workloads of resting, 1000, 2000, and 3000 (BTU h1) were 4.75 1.03, 8.09 1.39, 11.39 1.26, and 14.36 1.29 (mmHg s1). All CO₂ metrics had a statistically significant association and all positive slopes with increasing metabolic rate. No significant differences in CO₂ metrics were found between the three fitness groups.DISCUSSION: A standardized and automated methodology to calculate PIco₂ exposure level is presented and applied to characterize CO₂ washout in the EMU. The EMU has been operated successfully in over 400 extravehicular activities (EVAs) and is considered to provide acceptable CO₂ washout performance. Results provide a basis for establishing verifiable Pco₂ requirements for current and future EVA spacesuits.Kim KJ, Bekdash OS, Norcross JR, Conkin J, Garbino A, Fricker J, Young M, Abercromby AFJ. The partial pressure of inspired carbon dioxide exposure levels in the extravehicular mobility unit. Aerosp Med Hum Perform. 2020; 91(12):923931.