Sex Differences In Physiological Responses To Acute Hypoxia In Humans: Current Evidence And Directions For Future Research

Acute exposure (<48 hours) to hypoxic environments poses physiological challenges which are amplified during periods of exercise. This is important for individuals sojourning to higher elevations (>2,500m) due to the potential risk of developing altitude illnesses. Physiological responses to hypoxia are known, yet important knowledge gaps exist concerning sex differences. Direct comparison of studies is challenging due to differing methodologies. The present review critically evaluates current literature regarding cardiovascular and thermoregulatory responses to acute hypoxia, while highlighting areas for future research related to sex differences. Acute hypoxic exposure is characterized by decreased arterial oxygen saturation with a concomitant increase in ventilation and heart rate via stimulation of the autonomic nervous system. Despite similar heart rate and oxygen saturations between sexes, men demonstrate a higher sympathetic response to hypoxia compared to women. Cardiovascular alterations in cardiac output, stroke volume, and blood pressure occur upon exposure to hypoxia, with limited comparisons between sexes. Thermoregulatory responses to hypoxic exposure, in combination with cold, should be considered, due to potential implications for predicting altitude illness. Research remains limited and inconsistent, highlighting the need to prioritize sex-related comparisons during passive and exercise responses to hypoxic exposure, with implications for performance and altitude illness risk.