Oxygen breathing and ventilation
We investigated the ventilatory response to normobaric poikilocapnic hyperoxia in healthy subjects. The study was carried out in 26 subjects of the mean age 26 ±0.9 (SE) years, who breathed pure oxygen through a two-way valVE for 10 min. The subjects were in the sitting position with a mouthpiece and nose clip attached. Ventilatory flow was recorded using a pneumotachograph and minute ventilation was calculated from the tidal and frequency components. The SaO2 and alveolar CO2 tension were continuously monitored. Ten of the same subjects constituted a control group in which room air was substituted for oxygen and the tests repeated in the same way at another occasion. We found that oxygen breathing caused a transient 8.4% decline in ventilation, whose nadir was 1 min after the introduction of oxygen. Thereafter, ventilation increased significantly aboVE the baseline value and showed a further rising tendency toward the end of the test. We conclude that acute oxygen treatment is unlikely to haVE a major inhibitory effect on the carotid body-dependent ventilatory driVE in normal subjects. The determinants of the hyperoxic ventilatory stimulation remain to be established in further studies.