Joint NASA-ESA-DARA Study. Part three: effects of chronically elevated CO2 on mental performance during 26 days of confinement.

BACKGROUND: Short-term exposures to increased CO2 concentrations in breathing air up to 5% are assumed to have only negligible behavioral effects. In the present study it was examined to what extent prolonged exposures to moderately elevated levels of CO2 in the ambient air affect human performance.
METHOD: During two phases of 26 d of confinement in a diving chamber a group of four subjects was exposed to two different levels of CO2 (0.7% and 1.2%). Cognitive, visuo-motor, and time-sharing performance were assessed repeatedly before, during, and after the exposure by means of a task battery including grammatical reasoning, memory search, unstable tracking, and dual tasks. In addition, subjective workload and mood ratings were collected. A second group of four subjects served as a control group who performed the different tasks on the same 26-d time schedule without being exposed to confinement and elevated CO2.
RESULTS: During exposure to 0.7% CO2 only tracking performance was slightly disturbed compared with baseline levels, whereas performance of the control group remained stable. The time course of this effect suggested that it was related to chamber adaptation rather than to increased levels of CO2. During exposure to 1.2% CO2, tracking performance again was significantly impaired. In contrast to the lower exposure condition, the time course of this effect appeared to be related to the CO2 load and covaried with a loss of subjective alertness.
CONCLUSIONS: The study indicates that at least visuomotor performance might be affected by CO2 concentrations in the ambient atmosphere as small as 1.2% if subjects are chronically exposed to these concentrations in a confined environment. The strength of these effects, however, does not appear to be of operational relevance.