Brain cooling and respiratory heat exchange in camels during rest and exercise.

Respiration in relation to brain temperature (Tb) and body temperature (Tc) were investigated in two camels at rest and one during exercise (running at 10 km/h). The animals were subjected to natural ambient conditions (day: 25-30 degrees C, relative humidity (RH) about 65%; night: 15-20 degrees C, RH approx. 90%). They were studied when fully hydrated and during progressive dehydration by up to 15% of initial weight. At low Tc (less than 38 degrees C) Tb greater than Tc by approximately 0.2 degrees C, at higher Tc significant brain cooling was observed by as much as 1.5 degrees C during exercise. Minute ventilation (VE) and respiratory rate (f) increased with Tc such that tidal volume was constant and similar at rest and during exercise (Tc-Tb) increased linearly with f and hence VE. The cooling, dependent on turbinate heat exchange was related to certain features of the air flow pattern and f which have also been described in other large mammals.