Studies on Starling's Law of the Heart

Abstract

The applicability of Starling's law of the heart to the circulation of intact human subjects was studied by means of serial biplane angiocardiography utilizing injections into the left ventricle in nine patients, four of whom were unanesthetized. The end-diastolic and end-systolic volumes of the left ventricle were determined from the angiocardiograms by the method described by Dodge, and stroke volumes were calculated by subtracting the end-systolic from the end-diastolic volumes. In four patients large beat-to-beat variations in left ventricular end-diastolic volume occurred. These were accompanied by changes in stroke volume which varied directly with the preceding left ventricular end-diastolic volume. In four patients the left ventricular end-diastolic volume remained about constant, and in these patients the stroke volume showed little or no change. From these observations it was concluded that the ventricular stroke volume is a function of the end-diastolic volume and that therefore Starling's law of the heart is applicable to man. In the ninth patient pulsus alternans occurred; this was accompanied by concordant alternation of the left ventricular end-diastolic volume; i.e., the larger end-diastolic volumes resulted in larger stroke volumes and higher systolic pressures than did the smaller end-diastolic volumes. These observations are compatible with the concept that alternation of ventricular contraction can be explained by alternation of end-diastolic volume.