Environmental conditions and cardiac autonomic function during an Antarctic summer expedition at James Ross Island

Extreme environments impose significant demands on human physiological regulation, yet the specific environmental determinants of cardiac autonomic function during prolonged field deployments remain incompletely characterized. This study investigated associations between environmental conditions and heart rate variability during a 49-day austral summer expedition at the Johann Gregor Mendel Czech Antarctic Station on James Ross Island. Twelve participants were monitored using wearable electrocardiogram devices. Environmental data were recorded continuously from automatic weather stations and indoor sensors. Linear mixed-effects models with random intercepts and slopes for outdoor temperature were employed to investigate the relationships between environmental conditions and heart rate variability. Lower outdoor temperatures were associated with increased parasympathetic activity, with significant negative associations observed for RMSSD ([Formula: see text] [Formula: see text]), pNN50 ([Formula: see text], [Formula: see text]), SDNN ([Formula: see text], [Formula: see text]), and sample entropy ([Formula: see text], [Formula: see text]). Warmer indoor temperatures were independently associated with enhanced vagal modulation (RMSSD: [Formula: see text], [Formula: see text]; pNN50: [Formula: see text], [Formula: see text]; SDNN: [Formula: see text], [Formula: see text]). Lower outdoor temperatures were also associated with significantly longer R-R intervals ([Formula: see text], [Formula: see text]), consistent with cold-induced cardiac slowing. A progressive decline in heart rate variability was observed during the expedition, with RMSSD decreasing by approximately 22% over the 49-day period, while heart rate showed no significant temporal trend. Substantial inter-individual variability in autonomic temperature sensitivity was documented. These findings demonstrate that environmental conditions are associated with cardiac autonomic function through potentially distinct pathways, with implications for occupational health monitoring and the optimization of indoor climate in extreme environments.