THE RESPIRATORY RESPONSES TO ANOXEMIA OF UNANESTHETIZED DOGS WITH CHRONICALLY DENERVATED AORTIC AND CAROTID CHEMORECEPTORS AND THEIR CAUSES

Abstract

By techniques similar to those used on intact dogs, the effect of anoxemia upon the respiration of the unanesthetized dog, chronically deprived of carotid and aortic chemoreceptor control, was studied. In these animals, anoxemia causes stimulation as well as depression of the central respiratory mechanism. The depression of the minute volume of the respiration is transitory; it is not proportional to the degree of anoxia, and it is followed by a stimulation which causes a prolonged elevation of the minute vol., and an effective alveolar ventilation. The stimulation of the respiration induced by anoxia, in these animals, persists and the minute vol. is still further increased when the dogs are again permitted to breathe air. It is postulated that the respiration in the anoxemic deaf-ferented dog is the resultant of 2 antagonistic coexistent factors, a central depression and a central stimulation. The minute vol. of the respiration represents the algebraic sum of these effects. Although the central depression may vary in degree with the anoxia, the stimulation also increases with increasing anoxia, hence the depression of the minute volume is not greater as the anoxia becomes greater, for increasing stimulation cancels increasing depression. Recovery from the depression is more rapid than decay of stimulation, hence the greatly increased minute volume of respiration when air breathing is resumed. The evidence points strongly to a central chemical stimulation. Reasons are presented which preclude CO2 as the responsible agent.