A METHOD FOR INDEPENDENT AND REVERSIBLE EXCLUSION OF CHANGES IN ACTIVITY OF THE CAROTID CHEMORECEPTORS AND BARORECEPTORS: STUDIES ON SYSTEMIC HYPOXIA

Abstract

A method is described whereby, in the anæsthetized dog, changes in the activity of the carotid body chemoreceptors and carotid sinus baroreceptors can be independently and reversibly excluded. The carotid sinuses and bodies are isolated from the circulation and perfused at constant volume flow with arterial blood from the same animal. The perfusion pressure is controlled by means of a Starling type of resistance, the air‐space of which is connected to an artery so that the carotid sinus pressure is automatically maintained at the same level as the systemic blood pressure. Changes in carotid body chemoreceptor activity are excluded by perfusing the carotid bifurcation regions with arterial blood from a donor dog, the baroreceptors remaining functionally normal. Changes in activity of the carotid baroreceptors are excluded by maintaining constant the pressure in the air‐space of the Starling resistance, and therefore in the carotid sinuses; the carotid bodies are perfused with recipient dog's blood and remain functionally normal. Evidence is presented that in the vagotomized dog, reflexes from both the carotid chemoreceptors and baroreceptors contribute to the maintenance of the arterial blood pressure in acute systemic hypoxia produced by inhalation of 7–12 per cent O2 in N2. It is concluded that caution is necessary when interpreting the results of experiments based on observations made before and after interruption of the passage of nerve impulses in the carotid sinus or aortic nerves which contain afferent fibres to both types of receptor.