Evaluation of the heart pump function by afterload intracardiac pressure and blood flow measurements in cats.

In experiments carried out on cats and by using a mathematical model the authors studied afterload characteristics of the left ventricle of normal and hypertrophied heart. They found that afterload characteristics, expressed by a relationship between left ventricular systolic pressure and the aortic blood flow rate, have both in a normal as well as in a hypertrophied heart a nearly linear character, do not depend on the elastic properties of the aorta, and can be described by two parameters: the force parameter--i.e. maximum pressure at zero flow (Pm), and the rate parameter--i.e. the maximum flow value at zero pressure (Qm). Afterload characteristics change at inotropic influences: positive inotropic effects shift the characteristics upward and rightward, negative inotropic action shifts them downward and leftward. In moderate hypertrophy, Pm and Qm increase, with the increase in Qm being greater. The parameters of afterload characteristics can be used as pump function indexes characterizing the heart's ability to cope with the load in the outflow tract.