VENTRICULAR PERFORMANCE Inconsistency of the slope and the volume intercept of the end - systolic pressure - volume relationship as individual indexes of inotropic state in conscious dogs : presentation of an index combining both variables ALBERTO

We tested the ability of the slope (Emax) and the volume intercept (V0) ofthe end-systolic pressure-volume relationship (ESPVR) to indicate contractility changes in conscious dogs instrumented with sonomicrometers measuring left ventricular diameter in three orthogonal axes and a left ventricular pressure microtransducer. ESPVRs were generated by inferior vena caval occlusion under control conditions (C, and C2) and during enhanced (1+) and depressed (I-) inotropic states achieved by infusion of dobutamine and injection of propranolol, respectively. No significant difference between the first control (C,) and I + or between the second control (C2) and I were found for either Emax (C1, 5.31 + 1.68 mmHg/ml, mean + SD;I+, 5.37 + 1.44; C2, 5.20 1.62; I-, 4.18 + 1.32)orVO (C,, 10.3 ± 9.6 ml; 1+, 7.3 ± 9.1; C2, 9.9 ± 9.0; I-, 12.7 ± 12.5), despite significant changes in other indexes of contractility. Comparison of changes in Emax in individual animals in response to I+ and Irevealed that 63% were nonsignificant, 28% were significant and expected, and 9% were significant and paradoxical. Within defined volume limits and irrespective of individual changes in Emax and VO, in all animals I+ shifted the ESPVR above and to the left of C, and Ishifted the ESPVR below and to the right of C2. We thus integrated the changes in Emax and VO by measuring the area beneath each ESPVR between defined limits of end-systolic volume. The values for area were: C,, 612 150 mm Hgml; I+, 745 + 191 (p < .001); C2, 520 + 198; I-, 420 ± 139 (p < .001). We conclude that (1) neither Emax nor VO are individually reliable indexes of changed contractility, and (2) the area beneath the ESPVR between defined end-systolic volume limits is a consistent indicator of variations in inotropic state. Circulation 76, No. 5, 1115-1126, 1987. THE RELATIONSHIP between left ventricular pressure and volume at end-systole has been shown to be linear within the physiologic range. 1-10 Both in ViV. 5,7,12 vitro4 " andin vivo, the end-systolic pressure-volume relationship (ESPVR) is sensitive to changes in inotropic state and relatively insensitive to left ventricular loading conditions. This load independency represents the major advantage of the ESPVR over the traditional ejection phase and isovolumetric From the Research and Teaching Department of the Favaloro Foundation, Buenos Aires. Supported by grants from the Gregorio Pdrez Companc Company. Address for correspondence: Alberto J. Crottogini, M.D., Fundaci6n Favaloro, Depto. Investigaci6n y Docencia, Solis 453, 1078 Buenos Aires, Argentina. Received Dec. 2, 1986; revision accepted June 2, 1987. Presented in part at the 31 st Annual Meeting of the Argentine Society of Clinical Investigation, November 1986. Vol. 76, No. 5, November 1987 phase indexes of contractility, which are variably influenced by preload and afterload. 13 The variables defining the ESPVR are its slope (Emax) and its intercept (V.) on the volume axis. Controversy exists as to which of these two variables is the more reliable indicator of inotropic state. In isolated canine left ventricles, 3, 10 as well as in open-chest dogs, 14 changed inotropic state was shown to affect Emax with no significant alteration in V0. Similar results were reported by Sodums et al.7 and Lee et al.'5 in conscious dogs and by Mehmel et al.16 in humans. In conscious dogs, in which endsystolic diameter was used instead of volume, Mahler et al.5 found no significant changes in the Emax but did find significant displacements of the diameter intercept when varying inotropic state. Using the same approach, Sagawa et al. 17 observed that some conscious dogs of his series showed changed Emax, whereas others 1115 by gest on A ril 1, 2017 http://ciajournals.org/ D ow nladed from