Abstract
The question, is the response of the ventricle, under conditions of equal irritability, fundamentally determined by the initial length of its muscle fibers or by the initial tension exerted upon them, is of general physiological importance. The related question, can variations in initial volume (i.e., initial length) occur independently of changes in initial tension, in the mammalian heart, is of far-reaching clinical interest as well. As regards the second question, the experimental results of Frank 1 and those of Straub 2 supply an answer which is contradictory to that of Patterson, Piper and Starling 3 . The latter investigators believe to have demonstrated that initial length alone determines the magnitude of the cardiac response, irrespective of whether initial tension is simultaneously altered in the same or reverse direction. Gesell 4 holds that both factors may be concerned but seems inclined to believe that changes in initial length play their important rôle when ventricular filling is relatively small.
While the fact can not be denied that the bulk of evidence apparently points to the conclusion that initial length fundamentally determines the magnitude of contraction in skeletal muscles, it is not so clear how such changes can promptly adjust the work of the heart to sudden changes in venous inflow or arterial resistance—except, in so far as these length changes are primarily due to changes in initial tension. This thought is suggested by the following premises: The diastolic volumes of the ventricles can be increased beyond their normal capacity either (a) by an increased initial pressure overcoming the inherent tendency of the ventricles to resist stretching, or (b) by a reduction of this inherent power of the ventricle to resist stretching, i.e., by a reduction of tonus. 1
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