Pulmonary effects of submerged oxygen breathing in resting divers: repeated exposures to 140 kPa.

To detect cumulative effects of and check required recovery times between underwater exposures to 130-140 kPa oxygen, we assessed pulmonary oxygen toxicity after resting dives for four and six hours on two, five, and six or ten days, and three hours twice on each of two days. Despite a slight downward trend in diffusing capacity, four-hour resting dives could be repeated for at least ten days if intervals between them were 20 hours: 17% of divers had mild symptoms; 5%, mild changes in flow-volume parameters. In contrast, six-hour resting dives caused symptoms in 33% of divers. When dives were repeated daily (after 18 hours), but not with one day off (after 42 hours), changes in diffusing capacity accumulated, and hyperoxic myopia occurred after five dives. Divers complained of fatigue more with daily than with alternate day dives. When daily exposure was split into two three-hour dives, the incidences of symptoms and changes in pulmonary function depended on the surface intervals: on the second day, with two and 16 hours between dives, two three-hour dives were similar to a six-hour dive; with four and 14 hours, to a four-hour dive; with six and 12 hours, to a six-hour dive.