Post-dive bubble formation in rats: effects of exercise 24 h ahead repeated 30 min before the dive.

INTRODUCTION: Recent studies have shown that a nitric oxide releasing agent or a single bout of high-intensity exercise 20-24 h before a dive can prevent bubble formation following decompression. The aim of this study was to determine whether high-intensity exercise immediately prior to a dive eliminates the protective effect of a single bout of high-intensity exercise 24 h before the dive.

METHODS: Twelve female Sprague-Dawley rats were randomly divided into two equal groups. Group 1 performed 90 min of exercise twice, beginning 24.5 h and again 2.0 h before compression. Group 2 performed 90 min of exercise beginning at 25.5 h before compression. The standardized exercise protocol was 7 x 8 min at 85-90% maximal oxygen uptake (Vo2max) followed by 2 min at 50% Vo2max for a total of 90 min including a 20 min warm-up at 40-50% of Vo2max. All rats were exposed to a pressure of 700 kPa (7 ATA) for 45 min in a dry hyperbaric chamber followed by decompression to the surface at 100 kPa (1 ATA) at a rate of 50 kPa x min(-1) (0.5 atm x min(-1)) breathing air.

RESULTS: Bubble formation was significantly higher in rats that had exercised 24 h and 30 min prior to dive than rats that had only exercised 24 h prior to the dive (median bubble grade 4.5 vs. 0.5).

CONCLUSION: This study demonstrated that acute exercise prior to a dive eliminated the protection against bubble formation found 24 h after high-intensity exercise in rats.