Effect of oxygen at high pressure at rest and during severe exercise

Abstract

Two subjects (one an active athlete) performed severe exercise (1500 kg-m/min) either while breathing normal air or oxygen at 2 atmospheres absolute pressure (ATA). The sequence of breathing either air or oxygen was arranged according to one of three conditions. In the first condition exercise was performed twice, two hours apart, breathing air. In the second case exercise breathing air was followed by exercise in oxygen at 2 ATA after breathing oxygen at 2 ATA for 2 hr. In the last condition following preoxygenation with oxygen at 2 ATA for 30 min exercise was performed, subsequently a further 80 min was spent breathing oxygen and then the subject was decompressed on air, 40 min later the second exercise was performed in normal air. Levels of heart rate e, CO 2 , and O 2 were obtained during exercise and levels of pH, P CO 2 and P O 2 were measured pre and post exercise in arterial blood. Lactate (La) levels in venous blood were obtained pre and post exercise. Metabolic acidosis (La) in oxygen was reduced for the same exercise in both subjects (mean 8.8 mM/l) compared to normal air (mean 14.0 mM/l). This effect persisted for exercise in air after breathing oxygen for a long period and was more definite in the trained athlete (8.1 mM/l compared to normal air 12.3 mM/l) than the other subject (14.9 mM/l compared to normal air 15.7 mM/l). Exercise hyperpnea was reduced in oxygen and in air exercise after long oxygenation compared to normal air. The maximum exercise heart rate was reduced in oxygen but unaltered for any condition of air breathing whether or not preceded by oxygenation. Arterial hypocapnia occurred at rest breathing oxygen and a relative hypercapnia was apparent in oxygen after exercise. A large resting inspired-arterial oxygen tension difference developed in oxygen becoming larger during the course of oxygenation (168 mm Hg in 30 minutes and 506 mm Hg in 2 hours). Oxygen uptake and carbon dioxide elimination in air after oxygenation were depressed. These changes are attributed to the variation in relative importance of high arterial and tissue oxygen tension during oxygenation and the possible toxic effects of oxygen on enzyme systems in glycolysis which persist to air breathing exercise after long oxygenation.