Jm. Clark et al., HUMAN TOLERANCE AND PHYSIOLOGICAL-RESPONSES TO EXERCISE WHILE BREATHING OXYGEN AT 2.0 ATA, Aviation, space, and environmental medicine, 66(4), 1995, pp. 336-345
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.