RESPIRATORY AND CARDIOVASCULAR-RESPONSES TO INCREASED AND DECREASED CAROTID-SINUS PRESSURE IN SLEEPING DOGS

The purpose of this study was to determine the effects of changing blo od pressure in the carotid sinus (Pcs) on ventilatory output during wa kefulness and non-rapid-eye-movement sleep in unanesthetized dogs. Eig ht dogs were chronically instrumented so that ventilation, heart rate, and blood pressure could be measured while pressure in the isolated c arotid sinus was rapidly changed by means of an extracorporeal perfusi on circuit. Raising Pcs 35-75 mmHg consistently reduced ventilation 15 -40% in a dose-response fashion, with little or no further diminution in minute ventilation as Pcs was further increased >75 mmHg above cont rol level. This decrease in minute ventilation was immediate, due prim arily to a decrease in tidal volume, and was sustained over the 20-s p eriod of elevated Pcs. Increases in Pcs also caused immediate sustaine d reductions in systemic blood pressure and heart rate, both of which also fell in a dose-dependent fashion. The ventilatory and systemic ca rdiovascular responses to increased Pcs were the same during wakefulne ss and nonrapid-eye-movement sleep. Decreasing Pcs 40-80 mmHg caused a sudden carotid chemoreceptor-mediated hyperpnea that was eliminated b y hyperoxia. We conclude that increasing Pcs causes a reflex inhibitio n of ventilation and that this reflex may play a role in sleep-disorde red breathing.