Dehydration and body fluid regulating hormones during sweating in warm (38°c)
fresh and seawater immersion.
Hope, Arvid, Leif Aanderud, and Asbjørn Aakvaag.
1Norwegian Underwater Intervention a.s., PO Box 23 Ytre Laksevaag, 5848 Bergen,
Norway; and 2Haukeland University Hospital, 5021 Bergen, Norway
APStracts 8:0309A, 2001.
Body weight (BW) reductions of more than 4 kg have been observed during diving with
the open hot-water suit, a technique where 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 (HOI) experiments in 38°C fresh water (FW) and SW
for 4 h were performed. Average BW reduction was 2.5 and 1.9 kg in SW and FW HOI,
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 (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°C) and 38°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.
Received 25 February 2000; accepted in final form 18 May 2001
APS Manuscript Number A0182-0.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 29 June 2001