Variable Diastolic Ventricular Compliance : a General Property of Mammalian Cardiac Muscle

Abstract

STUDIES of the extensibility of quiescent cardiac muscle have been the cause of recurrent controversy. Starling's law of the heart relates the energy of contraction to the length the muscle fibres attain just prior to contraction. In studies of the regulation of cardiac contraction the assumption is made that measurement of pressure within the ventricle during diastole provides an accurate index of ventricular volume and that changes in pressure thus predict changes in fibre length¹. This assumption requires that the compliance of ventricular muscle, that is, the change in length for a given change in force, remain constant throughout diastole in spite of changing conditions. Although there have been indications in the older literature that the compliance or ‘tone’ of the heart may change during diastole as a dynamic variable², present interpretations of cardiac performance are based on the existence of constant diastolic extensibility³.