Carotid body control of bronchial circulation in sheep

The bronchial vascular response to chemoreceptor stimulation was studied in sheep anesthetized with alpha-chloralose, paralyzed with pancuronium, and artificially ventilated with room air. Blood flow through the common bronchial artery was measured with an electromagnetic flow-meter. Pressures were measured in the left atrium and aorta using appropriately placed catheters connected to pressure transducers. The carotid body was vascularly isolated and perfused at aortic pressure with blood of varied PO2 and PCO2. The viability of our preparation was assessed by the occurrence of a bradycardia in response to carotid body stimulation, and only data from animals demonstrating a bradycardia were analyzed. During hypoxic perfusion of the carotid body, heart rate decreased 6% (P less than 0.05). Bronchial blood flow increased by 46% and bronchial vascular resistance decreased by 23%, both of which were significant changes (P less than 0.05). During control experiments in which the carotid body was perfused with normoxic blood, there were no significant (P greater than 0.05) changes in any of the parameters. These data suggest that carotid body stimulation results in a reflex bronchial vasodilation.