Study On Heart Valve Mechanics Performance Based On Finite Element Analysis

Heart provides a steady blood flow to the whole body system by employing heart valves to maintain the unidirectional blood flow.Heart valves withstand about million times of opening and closing cycles in an adult lifetime,and undergo large deformation with complex stress and strain conditions during each cycle,resulting in calcification,tearing and other lesions.In order to improve the performance of artificial heart valves in the body,in vitro simulation tests are crucially important.Pulsatile flow tests that can effectively mimic the blood circulation environment,have been widely used to evaluate the hemodynamic property of artificial heart vales.In this thesis,a novel method combining the Pulsatile flow test and finite element analysis(FEA)was developed,which was further used to evaluate the relationships for the structure,mechanical property and hemodynamic performance of bioprosthetic heat valves.The pulse wave propagation characteristics in the blood were analyzed,including the stress-strain relationships under large deformation shown by MATLAB.The hemodynamic properties of artificial heart valves were tested by a pulsatile duplicator,including the cardiac output,mean aortic pressure and ventricular drive curve.FEA was employed to further analyze the stress distribution on heart valves at the microscopic level during the opening and closing cycles.Modal analysis was carried out to study the vibration features of the heart valves,whereas dynamic responses to mechanical loads at different frequencies were evaluated using the harmonic response analysis.The movement of heart valve leaflets with large deformation was analyzed using structure dynamic simulation,and the arbitrary Lagrange-Euler method was adapted to establish the fluid-structure coupling model between heart valves and blood,in order to evaluate heart valve movement under the blood circulation and provide the optimal parameters for artificial heart valve design.The FEA results showed that the stress along the central of the valve surface was the largest,and stress distribution exhibited axially symmetry characteristic.Performance of a bioprosthetic heart valve was evaluated using the pulsating flow test in vitro according to the ISO 5840 standard,and optimal valve performance was achieved using ventricular drive curves approximate to physiological conditions.The leakage percentage was found to increase with the increase of the mean pressure of aortic valves,while the effective opening area decreased by decreasing the cardiac output.FEA results revealed stress concentration in the belly and the commisure edge of the leaflets during the systole period,which underwent severe bending deformation.Stress concentration along the edges of the leaflet commissure and the leaf suture was found during the diastolic period,consistent with the theoretical calculation In addition,the valvular open areas and fluid velocities at different time points based on FEA results were close to those from experimental tests,indicating the reliability of the FEA method.