The effect of an increase in inotropic state and end-diastolic volume on the pumping ability of the feline left heart.

In isolated ejecting cat hearts, the pumping ability of the left heart was described quantitatively by the relationship between mean left ventricular pressure and mean left ventricular output. This relationship was determined by making the heart eject against a series of different loads on a beat-to-beat basis. Left ventricular mean pressure-mean output relationships of control and potentiated beats (at the same end-diastolic pressure) have a common intercept on the output axis but diverge toward the pressure axis. When the mean pressure values of the potentiated beats in a given experiment are multiplied by a single factor, superposition of the two relationships is obtained. A change in left ventricular end-diastolic pressure caused a more parallel shift of the left ventricular mean pressure-mean output relationship. Here, superposition could be obtained by using one multiplication factor for the mean pressure data and one for the mean output data of the relationship found after the change in end-diastolic pressure. We concluded that, using the left ventricular mean pressure-mean output relationship, changes in cardiac pumping ability caused by given changes in inotropic state and ventricular end-diastolic volume can be quantified by one or two multiplication factors, respectively.