Cross-adaptive effects of cold, hypoxia, or physical training on decompression sickness in mice

Abstract

For 14 or 28 days, groups of mice were handled (control); exposed discontinuously for 4 h to cold (4.degree. C) or hypoxia (P .apprx. 379 or 320 Torr); or exercised by swimming (15 min at 31.degree. C) or treadmill excursion (8.1 m/min for 1 or 1.5 h). The animals were divided into subgroups, exposed to 1 of 3 hydrostatic pressures (7.6-11.1 ATA) for 30 min, decompressed and were observed to determine survival rate or bends incidence (type II decompression sickness). Decompression sickness was significantly reduced (P < 0.05) in the treadmill-trained animals, was unchanged in cold-exposed and swim-exercised mice and tended to increase in animals adapted to hypoxia. Enhanced tolerance by treadmill training is presumably due to lean body conformation, which could reduce N2 saturation of tissues, and greater muscle capillarization and cardiovascular fitness, which may improve N2 elimination. Reduced tolerance with adaptation to hypoxia may be attributed to rheological changes associated with polycythemia, which facilitate bubble production.