Respiration in heat stressed camels.

Respiration and heat exchange in relation to brain temperature (Th) and body temperature (Tb) were investigated in four heat stressed camels subjected daily to high temperature (47 degrees C) in a climate chamber while resting when hydrated and dehydrated by approximately 10%, 15% and 20% of initial weight. Diurnally Tb followed patterns described previously. Th was usually 0.2-0.5 degrees C greater than Tb: occasional reversals with brain cooling were observed. Minute ventilation increased with Tb: above 37.5 degrees C it was approximately half as much in dehydrated as in hydrated animals. Respiratory frequency increased with Tb up to 60/min. Tidal volume fell with increasing frequency; above 25 breaths/min, tidal volume approximated dead space volume. Exhaled air was almost always unsaturated with no systematic effect of dehydration. Metabolic rate fell on dehydration reducing ventilatory demand. Th and Tb were measured in two of the animals walking outdoors: then Th fell below Tb if exercise exceeded 30 min. The data indicate that heat stressed camels pant, but turbinate vasoconstriction in a hot environment prevents cooling of the brain by carotid rete heat exchange.