Renal and hormonal responses to exercise in man at 46 and 37 atmospheres absolute pressure

Exercise increases plasma arginine-vasopressin (PAVP), plasma atrial natriuretic peptide (PANP), plasma renin activity (PRA), and plasma aldosterone (PALDO) in an intensity-dependent manner. With acute exercise, urine osmolality (UOSM) is often decreased despite increased PAVP. The hyperbaric environment lowers PAVP and UOSM, and increases urine flow.

If work produced similar renal effects at hyperbaria, greater than normal dehydration could result from larger free water losses.

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 exercise at 37 atm abs in 4 males.

This maximum exercise was performed at the highest pressure thus far reported and revealed no loss in peak power output. Maximum O2 consumption and heart rate were only 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, but basal and exercise-stimulated levels of PANP and PAVP were reduced compared with 1.5 atm abs control values. UOSM was not significantly affected during maximal exercise at sea level, but during maximum exercise at 37 atm abs and submaximum exercise at 46 atm abs UOSM increased over 300 mosm.kg-1 and 180 mosm.kg-1, respectively.

Contrary to the hypothesis, UOSM was increased by about 200 mosm.kg-1 by both exercise protocols during hyperbaric exposure and free water was conserved.