When Posture is Controlled, Acute Hypoxia does not Decrease Core Temperature

It has been reported that acute hypoxia causes a reduction in core temperature in humans. It was hypothesized that this occurs due to both a decrease in metabolic rate and an increase in skin blood flow. However, other studies have found that core temperature decreases with changes in posture. The methods in previous studies finding hypoxia to decrease core temperature did not control for postural changes. Thus, further examination is warranted to examine the effect of hypoxia on core temperature while controlling for posture change. Ten healthy adults, between the ages of 18 and 45 were recruited to participate. Subjects completed one trial consisting of breathing normoxic air (20.9%) for a 2 hour period and hypoxic air for a 1 hour period, while systematically changing posture. During this time core temperature and skin blood flow were recorded every 5 minutes. The results showed that mean core body temperature significantly (p < 0.05) decreased by 0.4℃ when the subjects transitioned from a standing to lying position. However, acute hypoxia, which reduced the mean oxygen saturation to 85%, did not significantly affect core temperature. Such results suggest that when posture is controlled, acute hypoxia does not significantly decrease core body temperature. Thus, the results of previous studies that have reported decreases in core temperature with acute hypoxia, but failed to control for posture, need to be questioned.