Acute normobaric hypoxia reduces body temperature in humans.

Anapyrexia is the regulated decrease in body temperature during acute exposure to hypoxia. This study examined resting rectal temperature (Trec) in adult humans during acute normobaric hypoxia (NH). Ten subjects breathed air consisting of 21% (NN), 14% (NH14), and 12% oxygen (NH12) for 30 min each in thermoneutral conditions while Trec and blood oxygen saturation (Spo2) were measured. Linear regression indicated that Spo2 was progressively lower in NH14 (p=0.0001) and NH12 (p=0.0001) compared to NN, and that Spo2 in NH14 was different than NH12 (p=0.00001). Trec was progressively lower during NH14 (p=0.014) and in NH12 (p=0.0001) compared to NN. The difference in Trec between NH14 and NH12 was also significant (p=0.0287). Spo2 was a significant predictor of Trec such that for every 1% decrease in Spo2, Trec decreased by 0.15°C (p=0.0001). The present study confirmed that, similar to many other species, human adults respond to acute hypoxia exposure by lowering rectal temperature.