Oxygen Toxicity. Respiratory Responses of Normal Men to Inhalation of 6 and 100 Per Cent Oxygen Under 3.5 Atmospheres Pressure

Abstract

The respiratory effects produced by successive inhalation of 6% O2 in N2, air and O2 at 3.5 atm. were studied in 6 normal men. The avg. results were as follows. O2 in the amt. of 3.5 atm. increased respiratory minute vol. about 26% and lowered alveolar pCO2 6.7 mm. Hg. The increased ventilation was entirely due to a greater tidal vol. and respiratory rate was not elevated. There was a slight rise in CO2 elimination. Admn. of 6% O2 in N2 at 3.5 atm. (equivalent to 21% O2 at sea level) produced no demonstrable effects excepting a 1.3-mm. Hg fall in alveolar pCO2, indicating that respiratory stimulation by O2 at increased ambient pressures is due largely to actions of O2 itself, not to the increased density of the inhaled gas. Air breathing at 3.5 atm. lowered alveolar pCO2 2.5 mm. Hg but produced no other significant changes. These and earlier observations in men breathing O2 at 3.5 atm. are discussed in relation to oxygen toxicity, the efficiency of alveolar ventilation at increased ambient pressure and the underlying causes of the respiratory stimulation by high inspired oxygen tensions. The most likely cause of oxygen hyperpnea appears at present to be central accumulation of CO2 resulting from decreased reduction of oxyhemoglobin.