Influence of Carotid Occlusion on Pulmonary Vascular Resistance in Anesthetized Dogs

Bilateral carotid occlusion in the spontaneously breathing, closed chest, chloralose anesthetized dog increased systemic arterial pressure and systemic vascular resistance, but was without effect on total pulmonary vascular resistance. Occlusion following bilateral vagotomy resulted in a significant decrease in pulmonary vascular resistance which was accompanied by an elevation in mean left atrial pressure. The fall in resistance was not changed after beta blockade; however, the administration of alpha blocking agents reduced the rise in mean left atrial pressure and systemic arterial pressure, and markedly attenuated the fall in pulmonary vascular resistance during occlusion. During carotid occlusion pulmonary vascular resistance was primarily controlled by passive effects arising from fluctuations in mean left atrial pressure and, therefore neurogenic effects appeared to be of little significance in the control of pulmonary vascular resistance in the carotid sinus reflex.