JOINT NASA-ESA-DARA STUDY - PART 2 - EFFECTS OF CHRONICALLY INCREASEDAMBIENT CO2 CONCENTRATION ON AEROBIC CAPACITY

As part of a joint NASA-ESA-DARA study on the effects of chronically i ncreased CO2 concentrations in ambient air, changes in parameters indi cating aerobic capacity were investigated by cycle ergometry. Two pote ntial sources for reductions of aerobic capacities were hypothized: 1) the adaptations to CO2 such as reduction in H+-buffer capacities whic h may influence muscle metabolism; 2)the reduced physical activities w hich may lead to a detraining effect. Four subjects were exposed to 0. 7% and 1.2% CO2 concentration in a confined compartment for 23 d each with 3 mo in between the two campaigns. A combined exercise test was a pplied before, during (on days 5, 11, and 22) and after CO2 exposure. Comparing steady-slates at 30 W and 80 W power, elevated ventilation w as found increased during CO2 exposure with significant differences be tween the two campaigns. Peak oxygen uptake decreased over the period of CO2 exposure, but was found not significantly different on day 5 co mpared to pre-exposure measurements. This decrease was not dependent o n the CO2 concentration. The lactate concentration at low exercise int ensities was found elevated during CO2 exposure. A shift in reverse di rection was observed after the CO2 exposure. Since peak oxygen uptake did not differ on day 5 and the lactate concentration was found increa sed, it was concluded that the potential changes in muscle metabolism by adaptation to elevated CO2 concentrations did not influence the aer obic capacities. Therefore, it was concluded that the changes in aerob ic capacities are the result of the reduced physical activities of the subjects while living in the confined compartment.