Effects of acute exposures to carbon dioxide on decision making and cognition in astronaut-like subjects

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.

Keywords: Psychology; Risk factors.

Conflict of interest statement

Competing interestsThe authors declare no competing interests.

Figures

Fig. 1

Means ± 95% confidence intervals of SMS measures at each targeted concentration of CO2. The raw scores assigned for each measure are linearly related to performance, with a higher score indicating better performance. Values are based on the relationship to established independent standards of performance among thousands of previous SMS participants. Measures for Initiative are the log-transformed values. *The threshold for significance used for post hoc comparisons by pairwise contrasts of adjusted predictions was p < 0.008, which was derived by dividing 0.05 by 6, the number of post hoc pairwise comparisons made

Fig. 2

Mean ± 95% confidence intervals of percentile ranks for SMS measures at targeted concentrations of CO2. Decision-making performance scores were converted to percentile ranks by indexing against scores of performance measured in more than 20,000 subjects ages 16–83 years who were chosen to represent the working population of the US. The baseline is composed of responses by a variety of members of this population, including students, professionals, homemakers, and laborers

Fig. 3

Percent change of SMS scores from baseline at elevated concentrations of indoor pollutants determined in several studies. When viewed as a percentage change from the baseline, the SMS measures that were most adversely affected differed among the studies but similarities in the set of most affected measures were greatest between the reports of Satish and Allen. In the Study of Allen most affected measures were the same for CO2 and VOCs. VOCs—volatile organic compounds

Fig. 4

Mean ± 95% confidence intervals of accuracy (a) and speed (b) for the 10 cognition measures by group at each of the targeted CO2 concentrations (600, 1200, 2500, 5000 ppm). p-Values refer to Type-III fixed effects of variance (with p < 0.05 indicative for at least one concentration differing from the overall mean)

Fig. 5

Evaluation of standardized scores of speed, accuracy, and efficiency across tests (higher scores reflect better performance). The p-values for significant differences in overall speed across tests achieved at different CO2 concentration are given on the graphs for Overall Speed. Error bars indicate the 95% confidence intervals

Fig. 6

Sequence and durations of events on days of exposure. The sequences and duration of tests and intervening rest periods on days of exposure are indicated on the time line