Progression of and recovery from pulmonary oxygen toxicity in humans exposed to 5 ATA air

Animal studies suggest that pulmonary oxygen toxicity proceeds more slowly in diluted oxygen breathing mixtures than in pure oxygen at the same inspired partial pressure. We exposed 12 healthy subjects to air at 5 ATA (PiO2 = 1.05 ATA) in a hyperbaric chamber for 48 h, and compared the rate of development of symptoms of O2 toxicity to rates seen in previous studies using 100% O2 at 1 ATA. Symptoms consisted of chest tightness, cough, substernal discomfort, exertional dyspnea, anorexia, nausea and vomiting, headache and digital paresthesias starting at about 12 h, and continuing several days into the recovery period. Pulmonary function changes consisted of significant decrements in vital capacity, flow rates, and DLCO. Initial recovery was in a 0.50 ATA oxygen atmosphere, with the majority of subjects showing definite recovery in both symptoms and pulmonary function. Subjects showed complete recovery in about 8 d, although symptoms of fatigue and exertional dyspnea continued for a month in some cases. In contrast, none of the above changes were noted in an additional 6 subjects exposed to a 5 ATA environment with 6% oxygen (PiO2 = 0.30 ATA). No change in resting gas exchange, as indicated by alveolar-arterial oxygen gradients, was detected in either group. Comparison of these data to that for pure oxygen studies reveals no significant difference in the progression or character of pulmonary oxygen toxicity.