Comparison of the reflexes elicited from combined or separate stimulation of the aortic and carotid chemoreceptors on myocardial contractility, cardiac output and systemic resistance.

Changes in left ventricular performance, stroke volume, and peripheral vascular resistance were studied in dogs after combined and separate stimulation of the aortic and carotid chemoreceptors. Selective stimulation of the aortic chemoreceptors produced an immediate increase in myocardial contractility as judged by the force developed by a strain gauge arch sewn into the left ventricular myocardium and by changes in the first derivative of the left ventricular pressure. Similar results were seen when heart rate changes were prevented by prior administration of atropine, when changes in outflow impedance were prevented by previous blockade of the alpha-adrenergic receptors, and when there was combined chemoreceptor stimulation. Betaadrenergic blockade prevented the increase in myocardial contractility observed after chemoreceptor stimulation. With selective carotid chemoreceptor stimulation there was no significant change in contractility. Aortic chemoreceptor stimulation increased the heart rate and peripheral vascular resistance, while stroke volume decreased; carotid chemoreceptor stimulation slowed the heart rate and increased the stroke volume, but not change peripheral vascular resistance. ADDITIONAL