How to quantify pump function of the heart. The value of variables derived from measurements on isolated muscle

Abstract

We show in this paper how pump function of the heart can be quantified. Subsequently, a number of quantities, determined in the intact heart but derived from the length-tension and force-velocity relationships found in isolated muscle are evaluated as descriptive of cardiac pump function. The interest in these quantities results from the relevant comparison between the function of heart and isolated muscle. Since so much basic information is available on the behavior of isolated muscle, this knowledge usually is taken as a basis for such a comparison. However we demonstrate for a number of variables derived in that way, that they cannot give a quantitative description of the heart as a pump. It seems to us that the efforts to understand cardiac pump function by applying muscle data and theory to the whole heart have entered a phase of diminishing returns. Another more fruitful possibility for bringing heart and muscle together seems to orient research in the opposite direction, i.e., to study isolated heart muscle as if it were part of the ventricular wall.