Evaporative cooling and respiratory alkalosis in the pigeon.

Abstract

Pigeons can tolerate exposure to air temperatures above 50[degree] C while maintaining body temperature at 43[degree] C. This is achieved by evaporation of water in an amount which must correspond to the sum of metabolic heat production and heat gained from the environment. At temperatures up to 40[degree] C, the increase in evaporation seems to be due to a deeper respiration (increased tidal volume), while respiratory frequency remains unchanged at about 30/min. There is no concurrent change in the Pco2 [CO2 tension] of the blood, which suggests that the increase in respiratory volume is achieved by the air sacs alone, without increase in the passage of air over the gas exchange surfaces of the lung. At temperatures above 45[degree]C the respiratory frequency is increased to about 650 cycles/min. and despite a reduction in estimated tidal volume, there is loss of CO2 and considerable alkalosis. The decrease in Pqo2 oi tne blood indicates a threefold increase of the passage of air over the gas exchange surfaces of lung.