Finite element analysis of the human left ventricle in diastole and systole
Previously, at Brunel University, two computer programs had been developed to facilitate the analysis of the diastolic material properties of the human left ventricle. These two computer programs consisted of; a finite element program, "XL1", which ran upon a Cray-1S/1000 and a post-processor and pre-processor, "HEART", which ran upon the Multics computer system. The computer program "HEART" produced the finite element model, which was then solved by "XL 1", and it also allowed for plotting the results in graphical form, The patient data was supplied by the Royal Brompton Hospital in the form of digitised cine-angiographic X-ray data plus pressure readings. The first stage was to transfer the two separate computer programs "HEART" and "XL 1" to the Sun Workstation system. The two programs were then combined to form a single package which can be used for the automated analysis of the patient data. An investigation into the effect that the elastic modulus ratio has upon the deformation of the left ventricle during diastole was performed. It was found that the effect is quite small and that using this parameter to match overall shape deformation would be extremely sensitive to the accuracy of the initial data. The main part of this work was the implementation of active cardiac contraction, by means of a thermal stress analogy, into the finite element program. This allows the systolic part of the cardiac cycle to be analysed. The analysis of the factors that affect cardiac contraction, including the material properties and boundary conditions was performed. This model was also used to investigate the effect that conditions such as ischaemia and the formation of scar tissue have upon the systolic left ventricle. The use of the thermal stressing analogy for cardiac contraction was demonstrated to mirror global and local deformation when applied to a realistic ventricular geometry.