Diastolic pressure-volume relationship in the canine left ventricle.

Analysis of the passive pressure-volume filling curve of the left ventricle demonstrates that heart size and ventricular geometry exert major effects on the pressure-volume curve in the absence of changes in intrinsic muscle stiffness. Because the pressure-volume relationship is curvilinear, both quantitative and qualitative comparison of pressure-volume curves from different hearts is difficult. In the fresh isolated canine left ventricle, the pressure-volume relation was found to be almost perfectly exponential throughout a range of filling pressures from 5 to 30 mm Hg. Therefore, a precise linear and quantitative expression of the pressure-volume relation (dP/dV = aP + b) was developed ( r = 0.995). The effect of isolated changes in either initial ventricular volume (mean Aa = 3.1?) or ventricular geometry (mean Aa = 27.1%) upon the slope, or a constant of this function was small in comparison to changes induced by rigor mortis (mean Aa = 45^). It was concluded that the a constant was primarily affected by changes in left ventricular wall stiffness. In this manner, comparison of the pressure-volume relationship from different hearts is possible, and the contribution of changes in wall stiffness may be quantified.