Oxygen cost of thermal panting

Abstract

Rectal temperature, respiratory rate, and oxygen consumption were measured in the unanesthetized ox at environmental temperatures of 15 C, 40 C (low humidity), during hyperthermia induced by increasing the humidity of the hot environment (40 C), and during localized heating of the anterior hypothalamus. In the cool environment (15 C), no statistically significant variations occurred in rectal temperature, respiratory rate, or oxygen consumption. In the hot dry environment, the mean rectal temperature increased by 0.5 C and an approximately 4-fold increase in respiratory rate occurred, but there was no significant change in the oxygen consumption. When the animals became hyperthermic in the hot humid environment, significant increases were detected in rectal temperature, respiratory rate, and oxygen consumption. At a rectal temperature of 41.4 C, the increase in oxygen consumption amounted to 67%. It was estimated that the oxygen cost of panting at this rectal temperature represented only 11% of the total oxygen consumption. Localized heating of the anterior hypothalamus resulted in a significant increase in respiratory rate but the concomitant increase in oxygen consumption was not statistically significant.