Studies on Starling's Law of the Heart. Ix. the Effects of Impeding Venous Return on Performance of the Normal and failing Human Left Ventricle.

DURING the last century t:he investigations of Fick, von Kries, and Blix, 1-4 on the strength of contraction of skeletal musele led to the concept t.hat the length and tension of the muscle at the time of stimulation determined the magnitude of its contractile response. Frank5 and later Starling0 as well as other investigators7-10 extended these observations to the heart, but the complex anatomy of this organ has made analogies to skeletal inusele difficult. Starling7 appreciated that they did not actually measure the length of the myo-cardial fibers in their experiments, but used measurements of ventricular end-diastolic volume to indicate changes in the fiber length. Similarly, these investigators utilized the mechanical acetivity of the ventricle, as reflected in the stroke volume and systolic pressure, to provide an index of the force of contraction. Many investigators have subsequently contributed to an understanding of the manner in which Starling's law is integrated into the regulation of the circulation, and have correlated ventricular end-diastolic volume (or an index thereof) and end-dia-stolic pressure with the cardiac output, stroke work, or a similar index.81-2 Following Wohlish and Clanman s observa-tions'3 on the resting length-tension relationships of excised muscle strips, Lundin14 carried out extensive experiments on the mechanical properties of resting and contraceting threads of frog ventricle. Length-tension relationships of isolated strips of myo.cardium were defined by Abbott and Mommaerts,'5 and by Sonnienblick,16 utilizing cat papillary muscle preparations, and by Blinks,17 working with rabbit atrium. Cotton and Malingo5 employing a Cushniy lever system, were the first to analyze the length-tension relationships of the dog's ventricle in situ, while Monroe and Franch'9 defined left ventricular pressure-volume relationships in an isolated dog heart preparation. The purpose of the present investigation was to examine the mechanical properties of funietioning human myocardium during isometric contraction. Particular attention was directed toward (1) determining the applicability of Starling's law to segments of human heart muscle, i.e., ascertaining whether the length of a segment of myocardium modifies its force of contraction ; (2) studying the relationship betweeni the length of a given segment of myocardium and the rate of development of tension; and (3) investigating some of the viscoelastic properties of the human myocardium. Methods Eleven patients (eight feimale amid three mnale), ranging in age fromi 5 to 43 years, with an average age of 22 years, were studied at the time of cardiac operation. Among them were five patients with atrial septal …