A new model for assessment of myocardial function: I. Description and performance norms.

Use of a new isometric rabbit-heart model, a modification of Langer's original preparation, has permitted independent assessment of myocardial perfusability in addition to contractility and relaxation. In this model an isolated, paced, interventricular septum contracts against a tension transducer and is perfused from another awake rabbit. Heparinized, diluted arterial blood is warmed and pumped at 1 ml/g-min. Perfusion pressure is measured by transducer. Each preparation serves as its own control. This model was used in determining performance norms for 68 preparations. Contractility was measured by maximum active tension, maximum rate of increase of tension and time to peak tension; relaxation by resting tension, maximum rate of relaxation and relaxation time; and perfusability by mean perfusion pressure and mean conductance. The status of the parabiotic rabbit was closely monitored. These studies have shown that the model is relatively simple, clearly defined and adaptable to a variety of experimental protocols.