Arterial impedance as ventricular afterload.

Abstract

Afterload, defined as the external factors that oppose the shortening of muscle fibers, is an important determinant of myocardial performance. Afterload must be measured and taken into account in any evaluation of ventricular performance. An operational definition of afterload appropriate to the intact ventricle is difficult to formulate. Difficulties inherent in measuring afterload are discussed. Experimental manipulations of ventricular afterload are reviewed. Vascular impedance and the advantages of defining afterload by the impedance spectrum rather than by instantaneous pressure or ventricular wall stress are stressed.