Abstract
Acute exposure to carbon dioxide (CO2) concentrations below those found on the International Space Station are reported to deteriorate complex decision-making. Effective decision-making is critical to human spaceflight, especially during an emergency response. Therefore, effects of acutely elevated CO2 on decision-making competency and various cognitive domains were assessed in astronaut-like subjects by the Strategic Management Simulation (SMS) and Cognition test batteries. The double-blind cross-over study included 22 participants at the Johnson Space Center randomly assigned to one of four groups. Each group was exposed to a different sequence of four concentrations of CO2 (600, 1200, 2500, 5000 ppm). Subjects performed Cognition before entering the chamber, 15 min and 2.5 h after entering the chamber, and 15 min after exiting the chamber. The SMS was administered 30 min after subjects entered the chamber. There were no clear dose–response patterns for performance on either SMS or Cognition. Performance on most SMS measures and aggregate speed, accuracy, and efficiency scores across Cognition tests were lower at 1200 ppm than at baseline (600 ppm); however, at higher CO2 concentrations performance was similar to or exceeded baseline for most measures. These outcomes, which conflict with those of other studies, likely indicate differing characteristics of the various subject populations and differences in the aggregation of unrecognized stressors, in addition to CO2, are responsible for disparate outcomes among studies. Studies with longer exposure durations are needed to verify that cognitive impairment does not develop over time in crew-like subjects.
Highlights
Adverse effects of carbon dioxide (CO2) on cognitive processes have been reported,[1,2,3] but the effects observed occurred at CO2 concentrations that were considerably higher than those deemed safe by regulatory agencies
It is possible that CO2 at higher concentrations mitigates effects of BEs and/or VOCs in this study, in view of the disparate outcomes among this study and the various studies that have assessed the effects of CO2 upon complex decision making[4,5,11] or general cognitive performance,[8,9,10] it seems most probable that differing characteristics of the various subject populations and differences in the aggregation of unrecognized stressors, in addition to CO2, were responsible for the varied, disparate, and conflicting outcomes among these studies
The current findings suggest that performance on Cognition is not relevantly affected if astronaut-surrogate subjects are exposed to CO2 concentrations of up to 5000 ppm for less than 3 h
Summary
Adverse effects of carbon dioxide (CO2) on cognitive processes have been reported,[1,2,3] but the effects observed occurred at CO2 concentrations that were considerably higher than those deemed safe by regulatory agencies. Because it is not unusual for CO2 levels aboard the International Space Station (ISS)[18] to exceed levels at which cognitive effects of CO2 were observed by Satish,[4] and because thresholds for some clinically significant effects of CO2 are considerably lower in space than they are on the ground,[18] it was important to determine whether the cognitive functions associated with complex decision making of crew-like subjects are affected by acute exposures to CO2 at concentrations that are routinely encountered aboard the ISS. To examine the significance of the effects of acute exposures to CO2 on cognition within the contexts of NASA’s needs for behavioral health management and toxicity assessment, we have used the SMS to determine if acute exposures to CO2, at or below operationally relevant concentrations, affects cognitive functions of astronaut-like subjects. The estimated means of all outcomes were in the bottom half or third of the scale
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