Dlastolic 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 δa=3.1%) or ventricular geometry (mean δa=27.1%) upon the slope, or a constant of this function was small in comparison to changes induced by rigor mortis (mean δa =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.