Effect of Carbon Dioxide Exposure on Physical and Cognitive Performance in a Simulated Spaceflight Contingency Scenario (Contingency_CO2_Walk)
Behavior and performance
Extravehicular Activity (EVA)
Life support systems
Scientific Name: Homo sapiens Species: Human
Ventilation systems in spacesuits provide oxygen and remove CO2 to allow for astronaut respiration. Exposure to elevated levels of CO2 is known to be detrimental to cognitive and physical health, and in the context of space flight missions, there is also an increased risk of injury during task performance. There are certain failure modes within the spacesuit that would require the opening of a helmet purge valve for mitigation. Once opened, this purge valve vents gas from the spacesuit to vacuum. This mechanism in turn affects the efficiency of CO2 washout within the suit, and likely expose astronauts to elevated levels of CO2. This study seeks to characterize the limit of acceptable cognitive and physical performance decrements and symptom severity for mission operations when subjected to these elevated inspired CO2 levels using standardized research techniques.
The two specific aims for this experiment include:
1. Quantify operational physical and cognitive performance across a range of inspired CO2 levels during simulated suited contingency EVA operations in a ground-based, shirtsleeve, laboratory study using standardized research techniques.
2. Qualify and quantify subjective metrics, including symptoms and self-assessment of performance experienced across a range of inspired CO2 levels during simulated suited contingency EVA operations in a ground-based, shirtsleeve, laboratory study using standardized research techniques.
This study will recruit 15 subjects for a ground-based simulation of a one-hour contingency walk back. The subjects will complete seven walk back sessions over the course of seven days and will be exposed to a different partial pressure of CO2 during each session. The subjects will be evaluated for both cognitive and physical performance. Specific CO2 related symptoms and self-assessment of performance will be evaluated via subjective questionnaire before, during, and after completing the walk. The subjective measures will evaluate three different hypotheses: 1) subjects will experience carbon dioxide-associated symptoms when exposed to elevated partial pressures of inhaled carbon dioxide, 2) increases in symptom severity will be observed with increasing partial pressures of inhaled carbon dioxide, and 3) self-assessment of performance will be impaired by increasing partial pressures of inhaled carbon dioxide, despite decrements in objective performance.
To test their hypothesis that cognitive performance (visual search, spatial memory, paired associate learning) during simulated EVA tasks will be reduced with increasing partial pressures of inhaled carbon dioxide, investigators will administer a validated cognitive test called the Digital Symbol Substitution Task (DSST) before, during and after the contingency walk. Additionally, validated, operationally relevant cognitive performance measures will also be used to quantify cognitive performance in a spaceflight-related environment. Example tasks include a subject's ability to regulate their translation speed, ability to respond to alarms, and ability to monitor consumables.
The study plans to test the researchers' hypothesis that physical performance (ambulation speed and distance) of simulated EVA tasks will be reduced with increasing partial pressures of inhaled carbon dioxide by evaluating the distance translated by subjects during the one-hour contingency walk. Subjects will be instructed to complete a minimum three-kilometer translation and not to exceed a subject-specific ambulation rate for more than two consecutive 20 second time intervals.
The investigators of this study expect to determine the maximum inspired CO2 level that still enables crewmembers to complete a one-hour contingency walk back within acceptable functional performance limits. In addition to testing the experiment hypotheses, the results are expected to inform xEMU suit design and operations and will be incorporated as a contingency inspired carbon dioxide standard for suited operations in NASA-STD-3001. Results are also expected to clarify the overall risk of CO2 exposure in the flight environment and will provide information on the physiologic, symptomatic, and performance effects of CO2 at various partial pressures including those at contingency levels.
Carbon dioxide (CO2)
Task performance analysis
Archiving in progress. Data is not yet available for this experiment.
Blood pressure systolic
Distance translated in 1-hour contingency walk
Duration of maintained effort
Heart rate (bpm)
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Heart rate variability
Mask inlet CO2 partial pressure
mask outlet C02 partial pressure
Oxygen partial pressure (PO2)
Transcutaneous carbon dioxide (TCO2)
Managing NASA Center
Johnson Space Center (JSC)
Responsible NASA Representative
Johnson Space Center LSDA Office
Project Manager: Jessica Keune
National Aeronautics and Space Administration (NASA)