Myocardial Mechanics: Tension-Velocity-Length Relationships of Heart Muscle

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Abstract
An animal preparation was developed in which it was possible to vary the flow and pressure presented to the left ventricle independently while maintaining a constant pressure and flow to the rest of the animal. Instantaneous left ventricular ejection rate, ventricular pressure, and the separation of 2 points on the epicardial surface were continuously measured with suitable instruments. Using these measurements and making certain assumptions about the shape and sequence of contraction of the heart, it was possible to calculate instantaneous muscle tension, rate of muscle shortening, and length of an assumed circumferential ring of muscle in the mid portion of the ventricle. It was found that at any instantaneous muscle length there was a reciprocal relationship between muscle tension and the velocity of shortening, consistent with the "force-velocity" relationship of A. V. Hill. Regression lines describing the relationship between tension and rate of shortening at a given instantaneous muscle length were seen to become progressively elevated with increasing length.