Contribution of hyperoxia to reduced pulmonary function after deep saturation dives.

Pulmonary function was measured before and after a 28-day saturation dive to a pressure of 0.25 MPa in eight subjects. PO2 was 40 kPa, with periods of 75 kPa for 2 h every 2nd day during the first 14 days, 50 kPa for the next 12 days, and a gradual fall to 21 kPa over the last 2 days in decompression. A 28-day saturation dive with six subjects to a pressure of 0.15 MPa and a PO2 of 21 kPa was used as control. The measurements included static and dynamic lung volumes and flows, transfer factor for carbon monoxide (TLCO), and a cycle ergometer exercise test. There was a significant reduction in TLCO of 9.8 +/- 6.0% (P < 0.001) after the dive when values were corrected for hemoglobin concentration changes. Effective alveolar volume was unchanged. There was a reduction in forced midexpiratory flow rate of 9.8 +/- 7.0% (P < 0.01), but forced vital capacity and forced expired volume in 1 s were unchanged. Peak oxygen uptake was reduced by 10.1 +/- 5.3% (P < 0.001). There were no significant changes in any of the lung function variables after the control dive. Exposure to raised PO2 contributes significantly to the changes in pulmonary function that have been reported after deep saturation dives to pressures of 3.1-4.6 MPa with a similar profile of oxygen exposure. TLCO is apparently a more sensitive index than vital capacity for oxygen toxicity.