Changes in the diastolic pressure-diameter relation after ventricular function curves

Systolic performance depends on end-diastolic muscle fiber length, contractility, and afterload. Ventricular function curves are constructed using end-diastolic pressure instead of end-diastolic dimensions, on the assumption that end-diastolic pressure and end-diastolic dimensions (reflecting muscle fiber length) have a constant relation. That assumption has been rejected. Theorectically, ventricular function curves should change with changes in the diastolic pressure-dimension relation as well as with contractility or afterload. We measured pressures and dimensions in ventricles of six open-chest dogs before and after opening the pericardium to alter diastolic pressure-dimension relations with afterload constant. When an indicator of systolic performance (developed pressure times diameter change during systole) was plotted against end-diastolic pressure, data obtained with the pericardium closed and open resulted in two distinct curves, suggesting an increase in contractility with the pericardium open. However, when systolic performance was plotted against end-diastolic diameter, data obtained with the pericardiumclosed and open fell along one curve, indicating no change in contractility. Therefore, changes in the diastolic pressure-dimension relation to shift conventional ventricular function curves.