Mechanical restitution and post extrasystolic potentiation of perfused rat heart: quantitative comparison of normal right and left ventricular responses.

Interval-force relationship of right and left ventricles of the isolated perfused rat heart was quantified by fitting polynomial, linear and mixed linear-exponential functions to the mechanical restitution (MRC) and post extrasystolic potentiation (PESPC) curves. Ventricular maximum developed pressure (Pmax) and its first derivative (dP/dtmax) were used as indices of contractility. MRCs and PESPCs could be separated into two distinct phases: phase A and phase B of MRCs; phase I and phase II of PESPCs. These phases for the right and left ventricle of the rat heart could be explained on the same model of cellular kinetics of the activator calcium, but showed distinct differences from other species. Right and left ventricle inotropic reserve (CRmax), as quantified from the centre of mass of the phase B of MRCs (from normalized Pmax), was (mean +/- SE): 132.4 +/- 2.05% and 132.1 +/- 1.7% at 1 Hz, which increased significantly (P less than 0.001) to 181.0 +/- 5.8% and 182.3 +/- 5.2% at 3.3 Hz, respectively. Linear regression of normalized right ventricle extrasystolic responses on the left ventricle responses gave a high correlation coefficient (typically r2 = 0.97). Time constants of the fitted mechanical restitution (TMRC) and post extrasystolic potentiation (TPESPC) curves were at 1 Hz, TMRC and TPESPC (from normalized dP/dtmax) were (mean +/- SE): 161.6 +/- 10.8 and 159.0 +/- 13.2 ms for right ventricle, and 196.1 +/- 14.5 and 188.3 +/- 10.7 ms for left ventricle, respectively. The results of this study indicate that interval-force relationship of the rat heart, as exemplified by CRmax and time constants of the fitted curves, could provide a useful index for quantifying and comparing right and left ventricular functions.