Optimal matching between canine left ventricle and afterload.

A parabolic relationship exists between ventricular external work and arterial load at given preload and contractility. Previous data indicate that the working point falls close to the parabola optimum. By combining the left ventricular (LV) end-systolic pressure-volume relationship (ESPVR) and an equation describing external stroke work, optimum values of stroke volume (SV), the slope (Emax) of the ESPVR, and arterial resistance (Rp) corresponding with the optimum (i.e., mSV, mEmax, mRp) were obtained. Experiments in anesthetized dogs were performed to test whether mSV, mEmax, and mRp also correspond to observed SV, Emax, and Rp at three different levels of volume load (right atrial pressure, RAP) before and after acute depression of LV contractility. Comparisons of observed and optimal values of SV, Emax, and Rp were made before and after LV depression. Before embolization, the ratios were SV/mSV 1.10-1.20 (RAP 5-15 mmHg); Emax/mEmax 1.21-1.41; and Rp/mRp 0.84-0.69. After LV depression, SV/mSV was 0.80-0.83, Emax/mEmax was 0.78-0.71, and Rp/mRp was 1.56-1.46. The ratios were all significantly changed (P less than 0.01) by the induced LV depression. The present analysis may offer a new tool to detect nonoptimal relations between cardiac and arterial functions.