PROBLEMS WITH USE OF THE END-SYSTOLIC PRESSURE-VOLUME SLOPE AS AN INDICATOR OF LEFT-VENTRICULAR CONTRACTILITY - AN ALTERNATE METHOD

The use of end-systolic elastance as a parameter of left ventricular c ontractility is based on a theory put forward by Sagawa (1) and is lim ited by an assumed linearity of the model for a time varying complianc e. A major problem is the contractility-dependent curvilinearity of th e end-systolic pressure-volume relationship (ESPVR), which may result in intercept volumes that are below a passive unstretched volume. Base d on the experimental data of Burkhoff et al. (2), we demonstrate the reasons for the lack of correlation of the slope (k) of the end-systol ic: pressure (P-es)-volume (V-es) relationship with ventricular contra ctility. A parabolic relation, P-es = a . V-es(2) + b . V-es + c, was used for approximation of the ESPVRs, as proposed by Burkhoff et al., and the slope (k = 2 . a . V-es + b), together with the volume axis in tercepts (V-0), calculated for the tangents for all P-es/V-es points o f the ESPVRs. The results demonstrate the volume range dependence of t he slope and V-0 of linear regression lines. However, intercepts of th e ESPVRs tangents with a midrange constant pressure line (e.g., 80 mmH g or 100 mmHg) justify the use of the shift of the end-systolic pressu re-volume relationship as a parameter of left ventricular contractilit y. This method appears to be valid over a much wider range of end-syst olic volumes than is the use of the slope alone.