HUMAN TOLERANCE AND PHYSIOLOGICAL-RESPONSES TO EXERCISE WHILE BREATHING OXYGEN AT 2.0 ATA

Multiple physiological functions were monitored in ten men who perform ed two 30-min periods of 150-W ergometer exercise during 120-min expos ures to O-2 at 2.0 ATA. There were no convulsions or electroencephalog raphic manifestations of increased excitability. Sequential measuremen ts of peripheral visual fields, pulmonary mechanical function, mental performance, and cardiovascular function during the resting recovery a fter each of the two exercise periods were not detectably altered from pre-exercise control values. Pre- and post-exposure measurements of v isual acuity, accommodation, pupil diameter, visual cortical activity, and retinal electrical activity also revealed no significant differen ces. While CNS symptoms were absent, average arterial PCO2 rose by abo ut 5 mm Hg during both exercise periods. This finding was confirmed in six subjects who performed four 6-min periods of continuous exercise at 50, 100, 150, and 200 W while breathing O-2 at 2.0 ATA. Average art erial PCO2 rose nearly linearly from 34.3 mm Hg at rest to 44.0 mm Hg at 200 W. Arterial PCO2-related increments in brain blood flow and PO2 may explain part or all of the known detrimental influence of exercis e on CNS O-2 tolerance.