Pre-dive exercise and post-dive evolution of venous gas emboli.

BACKGROUND: Recent studies have indicated that exercise before diving significantly reduces the number of circulating bubbles and the risk of decompression sickness. However, the most effective time delay between exercise and dive is not clear; the present aim was to resolve this.

METHODS: In a hyperbaric chamber, 10 men were compressed to 18 m for 100 min, then decompressed as per Royal Navy Table 11. Each subject performed three dives: a control dive and two after exercise performed either 24 h or 2 h before diving. Exercise consisted of 40 min submaximal work on a cycle ergometer. Venous gas emboli (VGE) were evaluated using precordial Doppler ultrasound immediately on surfacing, with measurements made at 5-min intervals for 30 min, and at 15-min intervals for at least 2.5 h total using the Kisman Masurel (KM) scale.

RESULTS: Exercise either 24 or 2 h prior to a dive did not reduce the median number of circulating VGE (median maximum KM grade: control, 2+; for both exercise dives, 3). Bubbles disappeared from the circulation faster after the control dive than the exercise dives. Time to median KM Doppler scores of zero were: control:120 min; 2-h group: 225 min; 24-h group: 165 min.

CONCLUSION: Cycling exercise prior to diving did not reduce the number of circulating VGE in comparison to control, in contrast to recent studies. A number of factors may be responsible for these findings, including type of exercise performed, wet diving experience, and disparity in Doppler measurement techniques.