Analysis of left ventricular behaviour in diastole by means of finite element method

The human left ventricle in diastole can be modelled as a passive structure with incremental internal pressure change being considered as the load. Recent developments in engineering stress analysis provide techniques for predicting the behaviour of structures with complex geometry and material properties, as is the case with the left ventricle. That which is most appropriate is the finite element method which requires the use of a large digital computer. The ventricles of 2 patients have been studied during diastole, the geometries having been derived from cineangiographic data (biplane), and the pressure by means of catheter-tip manometers. Various descriptions of myocardial stress/strain relations have been assumed and applied to the left ventricular wall in order to obtain the best match between the calculated and observed deformation patterns. The manner in which the value and distribution of stiffness in the left ventricle influences the shape change can therefore be determined, and possible clinical implications deduced

Stability of the human spine in neutral postures

The present study aimed to identify some of the mechanisms affecting spinal compressive load-bearing capacity in neutral postures. Two spinal geometries were employed in the evaluation of the stabilizing mechanisms of the spine in standing neutral postures. Large-displacement finite-element models were used for parametric studies of the effect of load distribution, initial geometry, and pelvic rotation on the compression stability of the spine. The role of muscles in stabilization of the spine was also investigated using a unique muscle model based on kinematic conditions. The model with a realistic load configuration supported the largest compression load. The compressive load-bearing capacity of the passive thoracolumbar spine was found to be significantly enhanced by pelvic rotation and minimal muscular forces. Pelvic rotation and muscle forces were sensitive to the initial positioning of T1 and the spinal curvatures. To sustain the physiological gravity load, the lordotic angle increased as observed in standing postures. These predictions are in good agreement with in vitro and in vivo observations. The load-bearing potential of the ligamentous spine in compression is substantially increased by controlling its deformation modes through minimal exertion of selected muscles and rotation of the pelvis