Air humidity and carotid rete function in thermo‐regulation of the goat

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Abstract
The effects of air humidity on respiratory rate were studied in conscious goats exposed to an air temperature of 33.degree. C. Before the experiments the animals were chronically implanted with hypothalamic thermodes and intravascular heat exchangers to manipulate hypothalamic and general body core temperatures. Raising air humidity from 37 to 96% at constant air temperature resulted in a rise of respiratory rate, an immediate increase in hypothalamic temperature and a delayed, smaller increase in general body core temperature. The rise of respiratory rate was smaller when general body core temperature was clamped at its control level, and was absent when hypothalamic and general body core temperatures were clamped at their control levels during the humid air phase. The effect of high air humidity on respiratory rate in goats is predominantly the result of a rise in hypothalamic temperature acting on local thermosensitive structures. The carotid rete heat exchanger apparently provides the thermal link between the evaporating surfaces of the upper respiratory tract and the hypothalamus. This function of the carotid rete heat exchanger is restricted to heat-stressed animals. In animals subject to central cooling no local effects on hypothalamic temperature could be observed when the temperature of the inspired air was altered from 33.degree. to -17.degree. C.