Sleep-Wake differences and circadian rhythms of heart rate variability in Antarctica: Effects of polar night and isolation on autonomic regulation.

Isolated, confined and extreme environments like Antarctic overwinterings present significant challenges to human psychophysiological adaptation. While previous evidence suggests that such conditions affect autonomic response, the extent to which human physiology adapts, in particular, the sleep-wake cycle and circadian rhythms, remains unclear. To assess the impact of prolonged isolation and the polar night on autonomic nervous system activity, we conducted an observational and longitudinal study at Belgrano II Argentine Antarctic station over a year-long campaign. Heart rate variability, a measure of cardiac autonomic modulation, was computed in 13 crewmembers over 24-hour periods every two months. Analysis revealed a decrease in parasympathetic regulation during wakefulness and an increase during sleep, in association with the increasing duration of isolation. At the same time, parasympathetic activity during sleep decreased during the polar night, suggesting a distinct seasonal effect. These findings offer novel insights into how isolation and the polar night influence autonomic regulation. Understanding these physiological adaptations is crucial for developing effective countermeasures to mitigate stress-related health issues in extreme environments.