Studies on Starling ' s Law of the Heart

IN THE experiments performed on the canine heart-lung preparation, Patterson, Piper, and Starling observed that when venous return was augmented, cardiac performance initially increased, but when venous return was elevated beyond a critical level, the performance progressively declined, i.e., there was a descending limb of the Starling curve.1-3 During the past 20 years a number of studies have been carried out in order to determine whether or not the human heart also exhibits a descending limb of the Starling curve. This problem has been explored by acutely reducing the venous return to the heart by either mechanical or pharmacologic means and determining the induced changes in the cardiac output, and in the venous, right atrial, or right ventricular end-diastolic pressures.4 In general, these studies have indicated that in patients without congestive heart failure, impeding the venous return results in a fall in the cardiac output, whereas in patients with congestive heart failure, small increases in cardiac output sometimes occur. In some of the studies the relationships between the changes in right heart filling pressure and cardiac output were inconsistent.5' 7It appeared that a more direct approach to this problem could be achieved by relating the end-diastolic pressure of the left ventricle to the mechanical activity of this chamber during alterations of venous return. In the present investigation, venous return was impeded by progressively inflating a balloon in the inferior vena cava while left ventricular end-diastolic pressure, output, and work were measured. The studies were performed in patients with and without clinical and