Left Ventricular Function Described in Physical Terms

Abstract

A description in standard physical terminology of the variations of the left ventricle in its role as a pump was derived. Left ventricular pressure, left ventricular outflow, and an external dimension of the left ventricle were measured in unanesthetized, active dogs during spontaneous activities and infusions of autonomic drugs. Secondary variables pertinent to a functional description of a pump were derived continuously from the primary variables by analogue computers. The derived variables included stroke volume, cardiac output, effective power, stroke work, average power, volume acceleration, rate of change of pressure, duration of systole, and heart rate. These techniques allowed a detailed description in meaningful terminology of the integrated effects on the left ventricle of such stimuli as sleep, startle, exercise, postural variations, and infusions of autonomic drugs. The descriptions of the variations in the characteristics of the left ventricle allow tests to be made of hypothetical cardiovascular control mechanisms. The use of standard, well-accepted, physical terminology allows the descriptions to be evaluated in different laboratories by totally different measuring techniques. The terminology used was contrasted with operationally denned or ambiguous terms such as "contractility" or "vigor of contraction."