Role of carotid sinus and cardiopulmonary reflexes on left ventricular dP/dt in cats.

Interaction between vagally mediated cardiopulmonary receptors and carotid sinus baroreceptors was studied in regard to cardiac contractility in anesthetized cats using vagal cold block and carotid occlusion. Cold block of the vagi produced a small but significant increase in left ventricular dP/dt and in arterial pressure. Carotid occlusion caused a greater increase in both parameters. The effects of each of these individual procedures were significantly greater when either intervention was tested in combination with the other. Cardiac sympathectomy reduced but did not abolish the reflex increase in cardiac contractility due to either procedure. Subsequent beta-adrenergic blockade eliminated the reflex change in the contractility. The study demonstrates that 1) both cardiopulmonary and carotid sinus baroreceptors participate in the neural control of cardiac contractility with the latter's role being dominant; 2) there is an apparent interaction between the two reflex mechanisms in which one reflex system acts to compensate the other's effects.