The relationship of various measures of end-systole to left ventricular maximum time-varying elastance in man

This investigation was designed to calculate left ventricular maximum time-varying elastance (E(max)), to define the relationship between E(max) and pressure-volume (P-V) relations at other, more easily defined measured of end-systole, and to determine whether these measures of left ventricular contractile function can be normalized in man. Accordingly, we studied 10 subjects with simultaneous high-fidelity micromanometer left ventricular and ascending aortic pressure recordings and biplane contrast cineangiograms at control conditions and during infusion of methoxamine and nitroprusside. E(max) was defined as the maximum slope of the linear relation of isochronal, instantaneous P-V data points obtained from each of the three loading conditions. Left ventricular end-systole was also defined for each loading condition as: the time of the maximum P-V ratio (maxPV), minimum ventricular volume (minPV), (-)dP/dt(min) [(-)dP/dtPV], and zero systolic flow approximated by the central aortic dicrotic notch (AodiPV). The mean heart rates and LV (+)dP/dt(max) were insignificantly altered during the three loading conditions. Isochronal E(max) ranged from 3.38 to 6.73 mm Hg/ml (mean 5.48 ± 1.23 [SD] mm Hg/ml) and the volume-axis intercepts at zero pressure ranged from -2 to 51 ml (mean 18 ± 16 ml). The isochronal slope calculations were reproducible (r = .97 to .99). The end-systolic P-V slope values for the maxPV, minPV, (-)dP/dtPV, and AodiPV relations correlated with isochronal E(max) (r = .90, .88, .69, and .74, respectively). The average slope values for these end-systolic P-V relations, however, underestimated the mean E(max) (p < .01 to p < .001). The mean extrapolated volume-axis intercepts for these end-systolic P-V relations also underestimated that for E(max). Finally, the isochronal E(max) and other end-systolic P-V relation slope values demonstrated inverse linear relationships with left ventricular mass (r = -.68 to -.91, p < .05 to p < .001). Only the E(max) volume-axis intercepts showed a linear relationship with left ventricular end-diastolic volume (r = .75). Thus we conclude that the time-varying elastic properties of the left ventricle can be calculated in man, that commonly used end-systolic P-V relations significantly underestimate isochronal E(max), and that normalization of isochronal E(max) and other end-systolic P-V relation slope values might be performed in man with left ventricular mass; no obvious relationship between volume-axis intercepts and measures of left ventricular or body size was apparent.