Breath holding after breathing of oxygen’

breathing of O2 seven untrained subjects held their breath beginning with a maximal inspiration. Breath-holding times ranged from 3. I to 8.5 minutes and ‘breaking-point ’ alveolar CO2 tensions from 5 I to gr mm Hg. Under these conditions, the maximum breath-holding time in minutes (x) can be related to the rise in alveolar CO2 tension in mm Hg (y), according to the equation x = o. I 3 y + I.4. After hyperventi-lation on 02, the breath-holding times were noticeably ex-tended ranging from 6 to 14 minutes, but the breaking-point alveolar CO2 tensions did not exceed those noted above. In all cases, the measured changes in lung volume can be ex-plained by the uptake of oxygen alone since the amount of CO2 is essentially unaltered during apnea. The decreases in lung volume observed are related to the total breath-holding time, about 13 minutes being required for a change in lun