RENAL AND HORMONAL RESPONSES TO EXERCISE IN MAN AT 46 AND 37 ATMOSPHERES ABSOLUTE PRESSURE

Background: Exercise increases plasma arginine-vasopressin (PAVP), pla sma atrial natriuretic peptide (PANP), plasma renin activity (PRA), an d plasma aldosterone (PALDO) in an intensity-dependent manner. With ac ute exercise, urine osmolality (UOSM) is often decreased despite incre ased PAVP. The hyperbaric environment lowers PAVP and UOSM, and increa ses urine flow. Hypothesis: If work produced similar renal effects at hyperbaria, greater than normal dehydration could result from larger f ree water losses. Methods: To test this hypothesis, hormonal and renal responses were assessed during exercise at 80% of maximum heart rate at 46 atmospheres absolute (atm abs) in 3 males, and during maximum ex ercise at 37 atm abs in 4 males. Results: This maximum exercise was pe rformed at the highest pressure thus far reported and revealed no loss in peak power output. Maximum O-2 consumption and heart rate were onl y slightly reduced, 9.5% and 7% respectively, despite a 41% reduction in maximum minute ventilation. Basal levels and the changes resulting from maximum exercise in PRA and PALDO were unaffected by pressure, bu t basal and exercise-stimulated levels of PANP and PAVP were reduced c ompared with 1.5 aim abs control values. UOSM was not significantly af fected during maximal exercise at sea level, but during maximum exerci se at 37 atm abs and submaximum exercise at 46 atm abs UOSM increased over 300 mosm.kg(-1) and 180 mosm.kg(-1), respectively. Conclusion: Co ntrary to the hypothesis, UOSM was increased by about 200 mosm.kg(-1) by both exercise protocols during hyperbaric exposure and free water w as conserved.