The use of left ventricular end-ejection pressure and peak pressure in the estimation of the end-systolic pressure-volume relationship

The end-systolic pressure-volume relationship (ESPVR) as derived from left ventricular pressure-volume loops has gained increasing acceptance as an index of ventricular contractile function. In animal experiments the ESPVR has been defined as a line connecting the upper left corners of several differently loaded pressure-volume (P-V) loops with a slope parameter Ees and a volume axis intercept parameter V₀. In the clinical setting, several variants of the ESPVR have been determined with use of peak left ventricular pressure, end-ejection pressure, and end-ejection volume. The maximum P-V ratio has also frequently been measured. We attempted to determine which of these alternatives resulted in good approximations of the reference ESPVR in eight isolated canine ventricles that ejected into a simulated arterial impedance system with resistance, compliance, and characteristic impedance. We determined various versions of the ESPVR from the same set of beats quickly obtained with little change in inotropic background. To vary ventricular pressure wave forms, each of the arterial impedance parameters was independently controlled at 50%, 100%, and 200% of normal. Against each of the nine combinations of the impedance parameters four P-V loops were obtained under four preloads and from each of the sets of four P-V loops, the reference ESPVR, linear regression of the peak pressure on end-ejection volume (ESPVR(PP-EEV)), and linear regression of end-ejection pressure on end-ejection volume (ESPVR(EEPV)) were determined. In addition, the maximum P-V ratio (MPVR) was calculated for each P-V loop. At all combinations of afterload impedance parameters ESPVR(PP-EEV) was shifted to the left (slope 5.4 vs 5.2 mm Hg/ml, intercept 6.6 vs 7.4 ml) and ESPVR(EEPV) was shifted rightward (slope 5.0 mm Hg/ml, intercept 7.7 ml) from ESPVR(REF). These differences, however, were quantitatively very small. MPVR was much smaller than the slope of ESPVR(REF) (4.0 vs 5.2 mm Hg/ml) and was load dependent. We conclude that as long as the P-V measurements are made under a fixed afterload system and different preloads, ESPVR(PP-EEV) and ESPVR(EEPV), but not MPVR, can be used to approximate ESPVR(REF).