Carotid Sinus Baroreceptor Reflex Effects upon Myocardial Contractility

Abstract

The reflex effects of stimulation of the carotid sinus baroreceptors on left atrial and ventricular performance have been studied in an auxotonic and an isovolumetric left heart preparation, which was innervated, though completely isolated hydraulically. Reflex changes of heart rate, arterial impedance, venous return, and level of circulating catecholamines were prevented from influencing cardiac performance. In the auxotonic preparation, stimulation of the carotid sinus baroreceptors decreased aortic pressure, cardiac output, and external left ventricular work. Simultaneously, mean left atrial pressure rose definitely. In the isovolumetric preparation, a decrease of the left ventricular peak systolic pressure was observed. These changes in atrial and ventricular dynamics were attributed primarily to a reflex negative inotropic effect directly upon the atrial and ventricular mycardium, mediated by the sympathetic nervous system. No definite changes in distensibility of the isovolumetric left ventricle were observed, although this could not be excluded in the auxotonic preparation. Primary changes in the coronary vascular bed were not considered to be responsible for the observed changes in atrial and ventricular dynamics.