Responsible Center: NASA JSC
Grant Monitor: Brocato, Becky
Center Contact:
becky.brocato@nasa.gov
Unique ID: 16092
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Solicitation / Funding Source: Directed Research
Grant/Contract No.: Directed Research
Project Type: Flight,Ground
Flight Program: ISS
TechPort: No |
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| Human Research Program Gaps: |
(1) BMed-101:Identify, quantify, and validate key selection factors for requisite performance on increasingly Earth-independent, long-duration, autonomous, and/or long-distance exploration missions
(2) BMed-108:Identify and characterize the potential impacts of combined spaceflight environmental stressors to inform both validated threshold limits and countermeasure for adverse C/P/Psy/N outcomes.
(3) EVA-201:Characterize impacts of variable atmospheric conditions on human health and performance, including exploration atmospheres, variable pressure suits, and alternate prebreathe strategies.
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| Task Description: |
Carbon dioxide (CO2) produced through the metabolism of astronauts inside spacesuits may accumulate during extravehicular activities (EVA). The maximum level of inspired CO2 during a 1-hour contingency walkback scenario is unknown. The CO2 Walk Back Study (See “Effects of Carbon Dioxide Exposure on Physical and Cognitive Performance in a Simulated Spaceflight Contingency Scenario”, PI Garbino), which is a companion study to this study, will characterize the limit of acceptable performance (cognitive and physical) decrements and symptom severity during a simulated 1-hour contingency walk back when individuals are subjected to elevated inspired CO2 levels (up to 30 mmHg) in the laboratory. However, there are concerns that the lower pressures, higher oxygen (O2) concentrations, and/or altered gravity environment that exist in the exploration spaceflight scenario may significantly impact the response to CO2.
The purpose of this study is to quantify the extent to which responses to CO2 are affected by the spacesuit atmosphere (reduced pressure with slightly elevated oxygen levels) and the spaceflight (altered gravity) environment. The high-fidelity EVA contingency walk back simulation task (which includes Virtual Reality and a treadmill) is not feasible to implement in the hypobaric and spaceflight environments, so this study will use an alternative EVA simulation task while recording the same physical and cognitive performance measures as the CO2 Walk Back Study. Results from this study will be used to either validate that CO2 dose-response relationships from the CO2 Walk Back Study are directly applicable to contingency EVA scenarios during exploration spaceflight, or else provide a recommended quantitative adjustment to dose-response relationships to account for the effects of the spacesuit atmosphere and/or gravity.
Together, these studies will help to determine the maximum allowable inspired CO2 level that will still enable crewmembers to complete a one-hour contingency EVA walk back within acceptable functional performance limits. Furthermore, as this study will include CO2 response data at nominal partial pressures of inspired CO2 in addition to contingency levels, this study will also inform and clarify overall risk of CO2 exposure in the flight environment – not just for suited EVA operations – which has been deemed an important human health and performance risk for future spaceflight missions.
Methods:
This study will use two experimental arms – a hypobaric chamber arm (n=16) and a flight arm (n=5). For each arm, we will use a repeated measures within-subject single-blinded design. In both the Chamber and Flight Arms, subjects will serve as their own control by undergoing the same experiments in a ground-based laboratory environment. The laboratory experiments will be performed in Johnson Space Center’s Building 21. The chamber experiments will be performed in the 20-ft Chamber in NASA Johnson Space Center’s Building 7. The flight experiments will be performed on the ISS. All experiments will be performed in a shirtsleeve configuration, using a cycle ergometer to simulate the metabolic rates of a contingency walk back scenario during a lunar surface EVA. During each experiment, subjects will repeatedly perform a standardized one-hour exercise and performance assessment protocol while being exposed to a breathing gas with varying partial pressures of inspired CO2. Physical performance will be measured by evaluating the duration subjects are able to maintain the target workload (up to a maximum of one hour) and quantifying the physiological (cardiopulmonary) effort to do the work. Cognitive performance will be quantified using the Cognition cognitive test battery (Basner et al., 2015) and repeated Digital Symbol Substitution Tasks (DSST). The severity of specific CO2-related symptoms and a subjective self-assessment of performance will be quantified via survey.
References: Norcross J, Abercromby AF, Alexander D. Maximum xEMU CO2 During Emergency Abort. 2020. Joint BRESCB/SMOCB Forum.
Basner M, Savitt A, Moore TM, Port AM, McGuire S, Ecker AJ, Nasrini J, Mollicone DJ, Mott CM, McCann T, Dinges DF, Gur RC. Development and Validation of the Cognition Test Battery for Spaceflight. Aerosp Med Hum Perform. 2015 Nov;86(11):942-52. |
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