Physiologic Response to Increased Oxygen Partial Pressure. Ii. Respiratory Studies.

The respiratory effects of a 30-day exposure to an alveolar partial pressure of 171 ram. Hg have been studied in 4 subjects at a total pressure of 700 ram. Hg (33.3 per cent 02 ) and 4 subjects at 258 mm. Hg (100 per cent oxygen). Vital capacities decreased on ascent to the 258 ram. Hg pressure ahitude and returned to normal immediately upon descent to ground level. Maximum breathing capacities increased concomitantly. No changes were seen in the 700 ram. Hg exposure. There was no evidence of changes in the oxygen carrying capacity of the blood: The lack of any persistent, unaccountable effects of an alveolar partial pressure of 171 ram. Hg in the presence or absence of nitrogen indicates that as far as pulmonary function is concerned, man appears to be able to tolerate either environment equally well. p REVIOUS REPORTS of respiratory effects of chronic exposures of man to decreased pressures and at higher than normal alveolar oxygen tensions have been restricted to exposures of 17 days or less.7, 9, 19.14 Changes in respiratory function noted in these experiments appear completely innocuous for these periods of exposure. However, it is difficult to predict possible changes in respiratory function for longer periods of time. In addition, the role of the Captain Robertson is from Sealed Environment Section, Environmental Systems Branch, Bioastronautics Dept., USAF School of Aerospace Medicine, Brooks AFB, Texas. Capt. Hargreaves is from Sealed Environment Section, Environmental Systems Branch, Bioastronautics Dept., USAF School of Aerospace Medicine, Brooks AFB, Texas. Capt. Herlocher is Chief, Sealed Environment Section, Environmental Systems Branch, Bioastronautics Dept., USAF School of Aerospace Medicine, Brooks AFB, Texas. Dr. Welch is Chief, Environmental Systems Branch, Bioastronautics Dept., USAF School of Aerospace Medicine, Brooks AFB, Texas. This work was supported in part by NASA Office of Advanced Research and Technology (NASA-Defense PR No. R-89) and Manned Spacecraft Center, NASA (NASA-Defense PR No. T-16758-G ). 618 Aerospace Medicine 9 July 1964 presence or absence of inert gas when the alveolar oxygen tension is increased is not dear ly defined. The Air Force atmospheric selection program requires that adequate information be available on the effects of "space equivalent" atmospheres on all physiological systems. This report deals with respiratory function studies undertaken in conjunction with other studies, to elucidate the question of physiologic effects of a 30-day exposure to higher than ambient oxygen partial pressures in the presence or absence of inert gas.