title: Dehydration and body fluid-regulating hormones during sweating in warm (38 degrees C) fresh- and seawater immersion.
abstract: Body weight (BW) reductions of more than 4 kg have been observed during diving with the open hot water suit, a technique in which heated seawater (SW) continuously floods the skin surface. To test the hypothesis that osmotic effects may be involved in these fluid-loss processes, head-out immersion experiments in 38 degrees C freshwater (FW) and SW for 4 h were performed. Average BW reduction was 2.5 and 1.9 kg in SW and FW head-out immersion, respectively (P < 0.01). Atrial natriuretic peptide increased during the first 30 min of SW immersion (5.6-13.4 pmol/l, P < 0.01) followed by a reduction to 7.6 pmol/l (P < 0.01). This paralleled an initial decrease in aldosterone (from 427 to 306 pmol/l, P < 0.05) followed by an increase to 843 pmol/l (P < 0.01). The effects of temperature on fluid loss were studied in thermoneutral (34.5 degrees C) and 38 degrees C SW for 2 h. In thermoneutral SW, calculated sweat production was negligible (0.05 kg) compared with 1.2 kg in warm SW. We recommend that, if a dive is planned to last for more than 4 h, a mandatory break for fluid intake should be incorporated in the diving regulations.
authors.affiliation: NUI AS, PO Box 23 Ytre Laksevaag, 5848 Bergen, Norway. ah@nui.no
authors.forename: A
authors.initials: A
authors.lastname: Hope
authors.forename: L
authors.initials: L
authors.lastname: Aanderud
authors.forename: A
authors.initials: A
authors.lastname: Aakvaag
mesh_terms: D000328:Adult; D000450:Aldosterone / Q000502:physiology; D001127:Arginine Vasopressin / Q000502:physiology; D009320:Atrial Natriuretic Factor / Q000502:physiology; D001826:Body Fluids / Q000502:physiology*; D001835:Body Weight / Q000502:physiology; D003681:Dehydration / Q000503:physiopathology*; D004231:Diuresis / Q000502:physiology; D005618:Fresh Water; D006728:Hormones / Q000502:physiology*; D006801:Humans; D007101:Immersion; D008297:Male; D009994:Osmolar Concentration; D012623:Seawater; D013546:Sweating / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000502:physiology
chemical_list: D006728:Hormones; D001127:Arginine Vasopressin; D000450:Aldosterone; D009320:Atrial Natriuretic Factor