ENERGY-EXPENDITURE AND FLUID PRODUCTION IN HYPERBARIC HE-O2 ENVIRONMENTS USING DOUBLY LABELED WATER

Energy expenditure (EE), carbon dioxide production (rCO2), water turno ver (rH2O), and urine production (UP) were measured to determine nutri ent requirements of U.S. Navy divers during saturation dives. Paramete rs were measured in a normal surface environment (n = 10) and in 0.56 MPa (n = 9) and 3.17 MPa (n = 11) helium-oxygen environments. Daily EE , rCO2, and rH2O were measured with the doubly labeled water method fo r 10-14 days in each environment. Daily UP was determined by 24-h urin e collection for 5- to 10-day periods in each environment. Divers cons umed a mixed diet composed of 30% calories from fat, 15% protein, and 55% carbohydrate. Both EE and rCO2 increased significantly relative to surface conditions at 0.56 MPa (13 +/- 4% and 11 +/- 4%) and 3.17 MPa (14 +/- 4% and 11 +/- 3%), but there was no difference between dives. Water turnover was not significantly affected by the hyperbaric envir onment. UP was significantly greater than surface conditions at 0.56 M Pa (53 +/- 19%) but not at 3.17 MPa (38 +/- 18%). Increased EE is attr ibuted to thermal stress caused by the helium-oxygen environment. Incr eased UP may have been caused by decreased evaporative water loss.