A novel design for the housing of bileaflet mechanical heart valves (St. Jude medical model) : a computational approach

The St. Jude Medical (SJM) bileaflet mechanical heart valve (MHV) was approved by the Food and Drug Administration in the late 70’s. The basic idea for the design of the valve is simply two semicircular flat plates pivoting on recessed hinges. The SJM valve provides improved hemodynamics compared to preceding MHV models. The overall performance of SJM valves, such as the symmetry of centralized blood flow, the complete opening of leaflets, and minimal pressure drop across the valve is satisfactory; however, non-physiological hemodynamics which may lead to red blood cell (RBC) lysis and thrombogenicity (often related to incomplete wash in the hinges area) still remains a major issue. In this thesis, a design improvement was proposed to the housing of the SJM valve. It is suggested that applying 10% ovality to the housing while its perimeter remains constant may improve the hemodynamics of the SJM valve significantly. In the first step, a quick computational platform was developed to assess the hemodynamic performance of the proposed design during the closing phase. Results indicated a clear hemodynamic improvement of the proposed design over the conventional design. In the next step, a novel computational platform was developed using computational fluid dynamics (CFD) method in order to evaluate the hemodynamic performance of the new design in details in the opening phase. Using this platform, the hemodynamic behavior of the proposed design was quantitatively compared to those of the conventional design. In particular, high shear stress zones, recirculation areas, velocity vectors in different sections and time phases, and the overall valve pressure drop for both conventional design and the proposed design were successfully investigated. Also, in order to evaluate the performance of MHVs at elevated heart rates (HRs), the proposed computational platform was successfully applied. Results indicated that hemodynamics was improved in the proposed design. This improvement is characterized by a lower pressure drop across the valve and lower shear stress zones in multiple locations compared to the conventional SJM valve. The proposed design shows promise and merits further development.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat