Breath holding after breathing of oxygen

Following normal breathing of O 2 seven untrained subjects held their breath beginning with a maximal inspiration. Breath-holding times ranged from 3.1 to 8.5 minutes and ‘breaking-point’ alveolar CO2 tensions from 51 to 91 mm Hg. Under these conditions, the maximum breath-holding time in minutes ( x) can be related to the rise in alveolar CO 2 tension in mm Hg ( y), according to the equation x = 0.13 y + 1.4. After hyperventilation on O 2 , the breath-holding times were noticeably extended ranging from 6 to 14 minutes, but the breaking-point alveolar CO 2 tensions did not exceed those noted above. In all cases, the measured changes in lung volume can be explained by the uptake of oxygen alone since the amount of CO 2 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 lung volume equal to the vital capacity. Three subjects were able to absorb their entire vital capacity volume during breath holding since no volume could be expired at the breaking point.