Effect of Intermittent Nitrogen Exposures on Tolerance to Oxygen at High Pressures

¹ From the Department of Physiology and Pharmacology, Duke University School of Medicine, Durham, North Carolina

If the exposure of guinea pigs to 4 atm. oxygen pressure is interrupted at 30-minute intervals with exposures to air or oxygen-nitrogen mixtures, the total survival time of the guinea pigs is significantly increased. Five-minute exposures to air increase the survival time by 40% with increasing benefits from 10-minute and 20-minute exposures to air. If the oxygen pressure is increased to 5.5 atm. the intermittent air exposures must be 20 minutes in length to significantly increase survival time. In addition to significantly increasing survival time intermittent air exposures have the apparent effect of reducing the frequency of convulsions. An explanation is advanced for the finding of a significant influence on survival at 4 atm. based on the observation that pulmonary damage is the usual cause of mortality at this pressure of oxygen. Since the pulmonary damage has been shown to be in large measure an atelectatic process a theory is proposed that nitrogen inhaled during the intermittent air breathing period is carried by the blood to those areas of the lungs in the process of collapse and the infiltration of nitrogen into the collapsing air sacs has the effect of reinflation, thereby delaying the process. This is not thought to be the sole mechanism responsible for the beneficial effects of intermittent nitrogen breathing on oxygen toxicity as it is not clear how such a mechanism could influence the convulsion frequency.