A model-based system for assessing ventricular chamber pressure-volume-dimension relationship: regional and global...

A system has been developed for measuring and relating in a non-beating isolated canine left ventricle dynamic changes in chamber pressure, volume, diameter, regional segment length, and wall thickness. The measurement system consists of a pulsatile blood pump whose stroke-volume and frequency can be adjusted selectively. The external pump system is used as a primary means for controlling instantaneous intraventricular volume. The relationship between left ventricular volume change, intraventricular pressure, minor axis diameter, and regional dimensions were studied as a function of pump rate. In addition to the basic constitutive properties, this system provided the means for measuring and comparing regional and global pressure-strain relationship including the effect of strain rate and its relationship to viscoelastic myocardial muscle model. The dynamic relationship between global dimensions and regional dimensions, circumferential segment length, and wall thickness were also investigated. The instantaneous relationship between intraventricular pressure resulting from periodic oscillations of chamber volume, including minor equator diameter, wall thickness, and regional segment dimensions were plotted and fitted to an exponential pressure-strain model, assuming a quasi-static large deformation. The observed difference between global and regional pressure-dimension strain stiffness coefficients can be attributed in part to basic constitutive and geometric considerations and not necessarily to the complex anisotropic or heterogeneous nature of cardiac muscle properties. This methodology provides indices which appropriately characterize the regional and global left ventricular chamber deformation and stiffness.