Pulmonary effects of submerged exercise while breathing 140 kPa oxygen

Pulmonary effects of prolonged mild intermittent underwater cycle ergometer exercise were assessed after single and repeated four-hour dives to 12 feet. With air, five daily dives (surface interval [SI], 20 hours), and with 100% oxygen, single dives, five daily dives, and afternoon-morning dives (SI, 15 hours) were conducted. Air divers had no symptoms or abnormal pulmonary function values but showed slight decreases within the normal range in forced expired volume in one second (FEV1; -0.45%/day) and forced expired flow between 25% and 75% of volume expired (FEF25-75; -0.8%/day). After one oxygen dive, incidences of mild symptoms or reduced pulmonary function were not different with exercise from those resting, but during five dives, decreases were significant in FEF25-75 (-1.8%/day) and diffusing capacity of the lung for carbon monoxide (D(L)CO; -1.2%/day), estimated to cause abnormal values in 25% of divers in nine to ten days. Following afternoon-morning dive pairs, changes in FEV1 and FEF25-75 were similar to those after nine or four daily dives, respectively. Exercise increases the injurious pulmonary effects of 140 kPa oxygen, and oxygen, those of exercise. A one-day break should follow two 4-hour exercise oxygen dives with surface intervals of 15 to 20 hours.