Pulmonary Oxygen Toxicity with Exercise: Single MK 25 Rebreather Dives or Split 6-Hour Exposures
2007
Shykoff, B.
Pulmonary effects of the MK 25 rebreather underwater breathing apparatus (UBA) were compared to those of the MK 20 open circuit UBA in single dives performed by 23 U.S. Navy divers. The apparatus was then used for split six-hour exercise dives on each of two days (three-hour dive, four-hour surface interval, three-hour dive, 16 hours overnight, repeat the dive sequence). Physical performance was measured in conjunction with the dives. Two sets of similar dives using the MK 20 UBA were then conducted with three days off between sets. Physical performance and total plasma antioxidant potential were measured. After the single dives, the incidence of respiratory symptoms (23%) or decreases in pulmonary function values (13% in flow-volume parameters, 4% in diffusing capacity) was no different from those after similar dives with the MK 20 UBA. After two days with the split six-hour exposures, combined results from the two MK 20 series yielded 44% of 21 subjects with symptoms, 44% with decreases in pulmonary function, and only 24% with neither. Only three of seven subjects could complete the series of four days with split six-hour exposures. Performance measures did not correlate with reported fatigue. Antioxidant results, while sparse, highlight interindividual differences.
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