Blatteau J-É, Gempp E, Balestra C, Mets T, Germonpre P. Predive sauna and venous gas bubbles upon decompression from 400 kPa. Aviat Space Environ Med 2008; 79:1100–5.Introduction: This study investigated the influence of a far infrared-ray dry sauna-induced heat exposure before a simulated dive on bubble formation, and examined the concomitant adjustments in hemodynamic parameters. Methods: There were 16 divers who were compressed in a hyperbaric chamber to 400 kPa (30 msw) for 25 min and decompressed at 100 kPa · min⁻¹ with a 4-min stop at 130 kPa. Each diver performed two dives 5 d apart, one with and one without a predive sauna session for 30 min at 65°C ending 1 h prior to the dive. Circulating venous bubbles were detected with a precordial Doppler 20, 40, and 60 min after surfacing, at rest, and after flexions. Brachial artery flow mediated dilation (FMD), blood pressure, and bodyweight measurements were taken before and after the sauna session along with blood samples for analysis of plasma volume (PV), protein concentrations, plasma osmolality, and plasma HSP70. Results: A single session of sauna ending 1 h prior to a simulated dive significantly reduced bubble formation [−27.2% (at rest) to 35.4% (after flexions)]. The sauna session led to an extracellular dehydration, resulting in hypovolemia (−2.7% PV) and −0.6% bodyweight loss. A significant rise of FMD and a reduction in systolic blood pressure and pulse pressure were observed. Plasma HSP70 significantly increased 2 h after sauna completion. Conclusion: A single predive sauna session significantly decreases circulating bubbles after a chamber dive. This may reduce the risk of decompression sickness. Sweat dehydration, HSP, and the NO pathway could be involved in this protective effect.