Asymptotic slope of log pressure vs log volume as an approximate index of the diastolic elastic properties of the myocardium in man.

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Abstract
The goal of this study was to develop, on a rational basis, an index of the intrinsic diastolic elastic properties of the left ventricle. A relatively simple analytic model employing a thin-walled spherical geometry coupled with an approximate formulation of a two-dimensional constitutive relation, was used to examine the primary determinants of the pressure-volume relationship of the intact heart. The results permit comparison with other indices of compliance or wall stiffness. The slope of the dP/dV vs P curve was found to be sensitive to the non-linear elastic constant K, but is also sensitive to variations in cardiac muscle volume. VdP/dV was found to be sensitive to pressure. m = d(log P)/d(log V) = (V/P)(dP/dV) is proposed as an index sensitive to K and relatively insensitive to both pressure and initial cardiac geometry. The index is compared with published studies. Using the data of Fester and Samet, mean values of the asymptotic log-log P-V slope, m, evaluated at end-diastole for normal, idiopathic hypertrophy, mild, moderate and severe coronary artery disease were 3.95 +/- 0.60 (SEM), 5.05 +/- 1.60, 5.24 +/- 0.96, 8.35 +/- 2.06, and 15.13 +/- 3.0, respectively. At values of LVEDP less than 7 mm Hg the concept of simple distension is questioned. The advantages and limitations of this approximate index are discussed. This index seems to afford a practical measure of the elastic properties of the wall over a rather wide range of pressure, volume, wall mass and wall thickness.