Effects of several cardiovascular drugs on various phases of circulatory dynamics

Abstract

This study shows some of the cardiovascular parameters which can influence cardiac output, all of which are in operation simultaneously. Changes in cardiac output were inconsistent, although each drug invariably produced characteristic directional changes in blood pressure and ventricular contractile force. During the administration of drugs the reflex response to cardiovascular changes were of prime concern in the regulation of cardiac output. The algebraic sum of the drug effect and the reflex homeostatic response to the drug determines the end changes in cardiovascular dynamics. Therefore, directional changes in cardiac output cannot always be categorically stated. The pressor drugs (epinephrine and levarterenol) which have a positive inotropic action usually produced an increment in cardiac output even though there was an increase in peripheral resistance to systolic ejection. The pressor drug methoxamine, which has little or no cardiac action, always produced a decrease in cardiac output consequent to the marked increase in peripheral resistance and reflex bradycardia. Nitroglycerin, a vasodilator with little cardiac action, decreased cardiac output associated with progressive peripheral pooling of blood; however, isoproterenol, a vasodilator with marked positive inotropic action, always produced an increment in cardiac output as a result of increased myocardial contractility and heart rate. Indeed, the value of pressorinotropic drugs over pressor drugs as supportive measures in shock therapy cannot be overemphasized.