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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 SaO(2) and alveolar CO(2) 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.