Interplay among carotid sinus, cardiopulmonary, and carotid body reflexes in dogs

Interactions among vascular reflexes evoked from carotid sinuses, carotid bodies, and cardiopulmonary region were examined in anesthetized, atropinized, and respired dogs with aortic nerves cut. The carotid sinuses were perfused at 220, 150, and 40-50 mmHg; the chemoreceptors were stimulated by perfusion with hypoxic hypercapnic blood. Cardiopulmonary vasomotor inhibition was interrupted by vagal cold block. Measurements were made of arterial blood pressure and of kidney and hindlimb vascular resistance. At sinus pressures less than 170-160 mmHg, cardiopulmonary vasomotor inhibition increased with increase in blood volume. At high sinus pressure, interruption of this augmented cardiopulmonary inhibition was as ineffective in changing vascular resistance as interruption of the lesser inhibition present during normovolemia. Chemoreceptor stimulation increased the response to vagal block at intermediate but not at high or low sinus pressure. The studies demonstrate the dominant role of the carotid sinus reflex when the three systems interact and the ineffectiveness of chemoreceptor stimulation when carotid or cardiopulmonary inhibition is maximal.