Lung function changes in divers after a single deep helium-oxygen dive.

INTRODUCTION This study measured pulmonary function in divers after a single helium-oxygen (heliox) dive to 80, 100, or 120 metres of sea water (msw). METHODS A total of 26 divers participated, of whom 15, five, and six performed a 80, 100, or 120 msw dive, respectively. While immersed, the divers breathed heliox and air, then oxygen during surface decompression in a hyperbaric chamber. Pulmonary function was measured twice before diving, 30 min after diving, and 24 h after diving. RESULTS At 30 min after the 80 msw dive the forced expiratory volume in 1 s (FEV₁)/forced vital capacity (FVC) ratio and the maximum expiratory flow at 25% of vital capacity (MEF₂₅) values decreased (89.2% to 87.1% and 2.57 L·s⁻¹ to 2.35 L·s⁻¹, P = 0.04, P = 0.048 respectively) but FEV₁/FVC returned to the baseline values by 24 h post-dive. Other pulmonary indicators exhibited downward trends at 30 min after the dive, but statistical significance was lacking. Interestingly, though several parameters decreased after the 100 msw dive, statistical significance was not reached. After the 120 msw dive, the FEV₁/FVC and MEF₇₅ decreased (90.4% to 85.6% and 8.05 L·s⁻¹ to 7.46 L·s⁻¹, P = 0.01, P = 0.007). The relatively small numbers of subjects who dived to 100 and 120 msw depths may explain the inconsistent results. The subjects diving to 100 and 120 msw were more trained / skilled, but this would not explain the inconsistencies in results between these depths. CONCLUSIONS We conclude that single deep heliox dives cause a temporary decrease in FEV₁/FEV and MEF25 or MEF₇₅, but these changes can recover at 24 h after the dive.