Body fluid regulation in a simulated disabled submarine: effects of cold, reduced O2, and elevated CO2.

INTRODUCTION: Survivors awaiting rescue aboard a disabled submarine (DISSUB) lacking power and/or environmental control would potentially be exposed to cold and reduced O2 and elevated CO2 levels. We hypothesized that elevated CO2 levels would lead to hormone changes that would mitigate cold and hypoxia-induced body fluid losses. METHODS: Blood was drawn from seven men on three mornings: baseline (21% O2, 0.05% CO2), after 4 d of low O2, cold, and high CO2 (T101; 4 degrees C, 16.75% O2, 2.5% CO2), and following acute withdrawal of cold and high CO2 (T173, 16.75% O2, 0.05% CO2). Total body water (TBW) was measured using deuterium oxide dilution at baseline and at T148. Hormone analyses included atrial natriuretic peptide (ANP), aldosterone (ALDO), and plasma renin activity (PRA). RESULTS: TBW decreased by 0.4 +/- 0.4 L. Water turnover was 3.0 +/- 0.5 L x d(-1). ANP (pg x ml(-1)) was lower (p < 0.05) at T101 (3.46 +/- 1.17) and T173 (4.97 +/- 2.28) vs. baseline (8.19 +/- 3.40). PRA (pg x ml(-1)) was higher (p < 0.05) at T101 (10.43 +/- 4.90) and T173 (14.23 +/- 4.48) vs. baseline (6.81 +/- 3.43). ALDO, serum osmolality, and electrolytes were not different across time. Urine flow was lower at T101 and T173 vs. baseline, and urine osmotic clearance was lower at T173 vs. baseline. Free water clearance did not change across time. DISCUSSION: These data indicate that the combination of cold, low O2, and high CO2 for 5-7 d did not change total body water and hormone changes and urinary measures across the DISSUB were consistent with fluid retention.