| Summary: | Objective.—To evaluate the role of the autonomic nervous system and adrenal system in acclimatization to cold in tropical men during short or prolonged sojourns at Antarctica.Methods.—The study was carried out on volunteers of the 18th winter over team (WOT) and 19th summer team (ST) of an Indian Antarctic Expedition. The ST members were evaluated at Delhi; during voyage; and on days 7, 30, and 60 of their stay at Antarctica. Identical studies were performed in WOT members who had stayed at Antarctica for 14 months. The parameters examined included heart rate, blood pressure, oral temperature, index finger skin temperature, heart rate variability, urinary epinephrine and norepinephrine, and salivary cortisol.Results.—The resting heart rate and blood pressure in ST members significantly increased (P < .05) on days 7 and 30 of their stay at Antarctica and returned to baseline Delhi values by day 60. The index finger temperature declined (P < .05) on day 7 at Antarctica and remained at lower levels during the entire period of observations. Heart rate variability showed an imbalance of autonomic nervous system effects with predominance of low-frequency band on day 7 of stay and returned to Delhi values by day 60. The urinary excretion of epinephrine and norepinephrine and salivary cortisol were also increased on day 7 and declined to baseline Delhi values after 2 months of stay. Compared with the ST group, the WOT group showed a significantly higher (P < .05) resting heart rate, blood pressure, and low-frequency power and urinary excretion of norepinephrine.Conclusions.—These observations suggest that Antarctic residency during austral summer results in gradual attenuation of sympathetic tone and a shift of autonomic balance toward the parasympathetic side. However, WOT members showed a predominance of sympathetic and adrenal activity compared with initial responses of ST members, suggesting deconditioning or possible resetting of the autonomic nervous system.
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