Abstract
Responses of the left ventricle to changes in afterload were tested in 11 open-chest dogs of which left atrial pressure was controlled arbitrarily. Maximal left ventricular dP/dt remained unchanged statistically against changes in afterload when left atrial pressure was kept constant, while it was changed with alteration of preload and by deterioration of left ventricular contractility induced by coronary ligation. Peak aortic flow velocity showed negative linear relationship against diastolic aortic pressure when left atrial pressure and left ventricular contractility were constant. This linear relation shifted downwards not only by reduction of contractility but also by lowering preload. Stroke volume also showed similar relationship, but abrupt decrease in stroke volume in higher range of aortic pressure. Effects of extracardiac factors on stroke volume which was ejected by constant ventricular contractility were considered to be complex.
Peak aortic flow velocity at 50mmHg of aortic diastolic pressure under the constant state of preload could be one of the indexes of ventricular function.
