Nasal heat exchange in a northern ungulate, the reindeer ( Rangifer tarandus)

When reindeer were exposed to low ambient temperatures, heat and water were recovered from the exhaled air by a nasal counter-current heat exchanger. Measurements of respiratory frequency, minute volume, exhaled air temperature and metabolic rate were made over a range of ambient air temperatures extending from −5.5 ° C to 27.2 ° C. At ambient air temperatures less than 10 ° C the exhaled air temperatures were an average of 21 ° C less than body temperature. The reduction of the exhaled air temperature at the lowest ambient air temperatures used in this study resulted in the recovery of 75% of the heat added and 80% of the water added to the inspired air on its way to the lungs. The heat and water recovered by the nasal temporal counter-current heat exchange in reindeer significantly reduced the metabolic cost of survival during cold exposure.