Objective: To investigate whether prehydration 90 min before a dive could decrease bubble formation, and to evaluate the consequent adjustments in plasma volume (PV), water balance and plasma surface tension (ST). Methods: Eight military divers participated in a crossover trial of pre-dive hydration using saline-glucose beverage (protocol 1) and a control dive with no prehydration (protocol 2). Drink volume was 1300 ml (osmolality 324 mOsm/l) and drinking time was 50-60 min. The diving protocol consisted of an open sea field air dive at 30 msw depth for 30 min followed by a 9 min stop at 3 msw. Haemodynamic parameters, body weight measurements, urine volume and blood samples were taken before/after fluid intake and after the dive. Decompression bubbles were examined by a precordial pulsed Doppler. Results: Bubble activity was significantly lower for protocol 1 than for protocol 2. PV increased after fluid ingestion by 3.5% and returned toward baseline after diving for protocol 1, whereas it decreased by 2.2% after diving for protocol 2. Differences in post-dive PV between the two conditions were highly significant. Body weight loss before/after diving and post-dive urine volume after diving were significant in both protocols, but the relative decline in weight remained lower for protocol 1 than for protocol 2, with reduction of negative water balance due to higher fluid retention. There were no differences in ST after fluid intake and after diving for the two protocols. Conclusion: Pre-dive oral hydration decreases circulatory bubbles, thus offering a relatively easy means of reducing decompression sickness risk. The prehydration condition allowed attenuation of dehydration and prevention of hypovolaemia induced by the diving session. Hydration and diving did not change plasma surface tension in this study.
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