Physical Performance in Inhaling Different Partial Pressure of Oxygen

Abstract

The cardio-respiratory function was observed during treadmill exercise inhaling different partial pressure of oxygen. The inspired air contained 14% O_2 (Po_2 102 mmHg), 21% O_2 (Po_2 159 mmHg), and 60% O_2 (Po_2 448 mmHg). The air in the decompression chamber was Po_2 100 mmHg which was equivalent to about 3,700m altitude. The endurance running time to exhaustion on the treadmill, maximum oxygen intake, maximum cardiac output, and maximum pulmonary ventilation were measured on 9 male subjects from 23 to 29 years of age. They were submitted to the maximal exercise by a motor driven treadmill inhaling the four different contents of O_2 levels mentioned above. The oxygen intake was measured by Douglas bag method. The CO_2 rebreathing technique described by K. Klausen was used for determining cardiac output. The heart rate and the respiratory frequency during exercise were continuously recorded. The gas samples were analyzed by micro-Scholander's apparatus, The running time to exhaustion on a treadmill in nine subjects were 3 minutes 28 seconds, 5 minutes 43 seconds, 7 minutes 37 seconds, and 3 minutes 37 seconds in the average, when the subject inhaled the oxygen of 14%, 21%, 60%, and the air in the decompression chamber respectively. There was found a close relation between physical endurance time and maximum oxygen intake, whereas the maximal cardiac output was kept unchanged despite of changing inspired oxygen contents. No consistent changes in the lung diffusing capacity were observed from ordinary air to low O_2 inhalation during maximal exercise. The results suggested that decreased maximum oxygen intake at low O_2 inhalation was due to incomplete oxygenation of arterial blood due to the reduced Po_2 in the inspired air.