The pumping ability of the left heart and the effect of coronary occlusion.

In an isolated preparation of cat heart we studied the pumping capacity of the left heart while left atrial filling pressure was kept constant. We used the source impedance concept to quantify the pumping capacity. In this source impedance concept the relation between left ventricular output and left ventricular pressure is given by the formula (see article) where Zs = source impedance, Plv = left ventricular pressure, Iao = flow in the ascending aorta, and omega = 2pif, f being frequency.. The pressure obtained at zero flow is called the hydromotive pressure (HMP). Only the mean values of pressure and flow were studied. We studied the behavior of 10 hearts in three different experimental situations and in the following sequence: (1) control conditions, (2) after ligating a part of the left coronary arterial system, and (3) after restoring left ventricular output to control level by raising left atrial filling pressure. It was found that source resistance was not significantly different in the three situations but that mean hydromotive pressure (HMP) was significantly lower after ligation of a part of the left coronary arterial system. It was concluded that the decrease in pumping capacity of the left heart after infarction can be compensated for almost completely by an increase in left atrial filling pressure. This compensating mechanism therefore seems to be very efficient.