Physiological responses to elevated carbon dioxide concentration and mental workload during performing MATB tasks

Abstract

Fifteen healthy male college-age students were exposed in an enclosed environmental chamber to investigate their physiological responses to elevated carbon dioxide (CO2) concentration and mental workload. During each CO2 exposure condition (1626 ± 306 ppm, 3562 ± 259 ppm and 5087 ± 318 ppm), a resting test was conducted first, and then the multi-attribute tasks with three different mental workload levels were performed in the order designed by the Latin square method. The breathing, electrocardiogram (ECG) and electroencephalogram (EEG) data were collected overlapping the period when participants were in the resting and task tests. The statistical analyses indicated that the elevated CO2 concentration had positive correlations with the breathing wave amplitude, the percentage of adjacent normal-to-normal intervals that differ from each other by more than 50 ms (pNN50), and the beta relative power of EEG during the task tests, but no significant response was observed during the resting test. The elevated mental workload was associated with increased arousal level as indicated by the decreased standard deviation of the normal-to-normal interval (SDNN), increased respiration rate and higher beta relative power of EEG, which could help explain the inverted U-shaped effect of mental workload on task performance. The physiological responses indicated that more effort was required to accomplish tasks when participants were exposed to high CO2 concentration or heavy mental workload, which led to a direct impact on task performance. The order of CO2 exposures was not balanced among the participants, which should be considered as a major limitation of this study.