Objective: To evaluate the effects of a sub- maximal exercise performed 2 hours before a simulated dive on bubble formation. To observe the hemodynamic changes and their influence on bubble formation.
Material and methods: Sixteen trained divers were compressed in a hyperbaric chamber to 400kPa for 30 min and decompressed at a rate of 100 kPa.min-1 with a 9 min stop at 130 kPa (French Navy MN90 procedure). Each diver performed two dives 3 days apart, one without exercise and one with exercise before the dive. All subjects performed a 40 min constant load submaximal and calibrated exercise which consisted of outdoor running 2h prior to the dive. Circulating bubbles were detected with a precordial Doppler at 30, 60 and 90 min after surfacing. Hemodynamic changes were evaluated with Doppler-echocardiography.
Results: A single bout of strenuous exercise 2h prior to a simulated dive significantly reduced circulating bubbles. Post-exercise hypotension (PEH) is observed after exercise with reductions in diastolic and mean blood pressure (DBP and MBP), total peripheral resistance were unchanged. Stroke volume (SV) was reduced whereas cardiac output (CO) was unchanged. Simulated diving caused similar reduction in CO independently of pre-dive exercise, suggesting that pre- dive exercise only changed DBP and MBP caused by reduced SV.
Conclusion: A single bout of strenuous exercise 2h before a dive significantly reduced the number of bubbles in the right heart of divers and could protect from decompression sickness. Declining stroke volume and moderate dehydration induced by a pre-dive exercise might influence inert gas load and bubble formation.
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