Pulmonary effects of repeated six-hour normoxic and hyperoxic dives

This study examines differential effects of immersion, elevated oxygen partial pressure, and exercise on pulmonary function after series of five daily six-hour dives at 130 kPa (1.3 ATA), with 18 hours between dives. Five cohorts of 10 to 14 divers participated. The exposure phases were resting while breathing O(2) or air in the water (“wetO(2)”, “wetAir”) or O(2) in the hyperbaric chamber (“dryO(2)”), and exercise in the water while breathing O(2) or air (“wetO(2)X”, “wetAirX”). Respiratory symptoms were recorded during and after each dive, and pulmonary function (forced flow-volume) was measured twice at baseline before diving, after each dive both immediately and on the following morning, and three days post diving (“Day+3”). The incidences of symptoms and of flow volume changes from baseline greater than normal limits (“ΔFV”) were assessed, as were mean ΔFV. The parameters examined were forced vital capacity (FVC), forced expired volume in 1 second (FEV(1)), and forced expired flow from 25% to 75% volume expired (FEF(25–75)). The phases ranked from greatest to least fraction of diver-days with symptoms were wetO(2)X (56%) > dryO(2) (42%) > wetO(2) (13%) > [wetAir (2%) or wetAirX (1%)] (p<0.05). FEV(1) and FEF(25–75) were depressed in the morning following wetO(2) and wetO(2)X and on Day+3 after and wetO(2)X, but increased immediately following each wetAirX dive. O(2) exposures caused symptoms and ΔFV suggestive of pulmonary oxygen toxicity,exacerbated by exercise. Indices of small airway function showed late (17-hour) post-O(2) exposure deficits, but, particularly with exercise, improvement was evident early after exposure with or without O(2). FEF(25–75) and FEV(1) remained depressed on Day+3 after wetO(2) and wetO(2)X.