Determining how different levels of indoor carbon dioxide affect human monotonous task performance and their effects on human activation states using a lab experiment: a tracking task

Different individuals respond differently to carbon dioxide (CO₂) levels in the local atmosphere. We aimed to determine whether brain activity changes with various CO₂ concentrations and whether this is correlated with heart rate and arterial oxygen saturation (SPO₂). We used electrocardiograms, SPO₂ measurements, electroencephalograms, and task performance metrics in various CO₂ concentrations and studied the changes in these metrics. We found that SPO₂ did not change in various CO₂ conditions; elevations in CO₂ up to 4000 ppm had no measurable influence on ventilation and SPO₂, suggesting no effect on monotonous task performance seen in terms of the alpha wave band rate. However, heart rate increased as early as within 15 min. We found that some individuals who naturally have lower SPO₂ values tended to undergo faster lowering of arousal level. Practitioner summary: SPO₂ may be an individual characteristic that affects the human ability to maintain concentration in monotonous tasks in enclosed spaces, such as driving a car. This study highlights the fact that different individuals respond differently to various CO₂ levels, based on SPO₂ levels, as manifested by decreased concentration and brain activity. Abbreviations: CO2: carbon dioxide; SPO2: arterial oxygen saturation; HR: heart rate; PaCO2: partial pressure of carbon dioxide; EEG: electroencephalography; ECG: electrocardiography; EOG: electrooculogram; HF: high-frequency; LF: low-frequency; ANOVA: analysis of variance; RRI: R-R interval ; Type 1: sensitive group; Type 2: non-sensitised group.