MYOGRAPHIC STUDY OF THE CAT'S HEART: EFFECT OF CHANGES IN VENOUS RETURN AND IN PERIPHERAL RESISTANCE ON VENTRICULAR CONTRACTION

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Abstract
In open chest anesthetized cats 3 methods of myographic analysis were studied. Two of these methods have been previously described, viz., Cushny''s Weighted Myograph and the imbedded artery segment. The 3d method (Dynamograph) permitted study of a constant area of heart muscle in spite of changes in heart diam. The theory was substantiated that the ventricle resembles physically an- elastic hollow sphere. It was found that though changes in initial tension alter the ability of the heart muscle to shorten directly, changes in initial length do not. In the latter instance the change in work performance is brought about merely by a change in the mechanical advantage. Thus as the fiber length increases, the ventricular diam. enlarges. Since it is a sphere, the area increases as the radius squared while the volume increases as the radius cubed divided by 3. Under these conditions the mechanical advantage of the ventricle is decreased but the volume output per unit of muscle shortening is increased. The fallacies and pit-falls of myographic recording are discussed.

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