Evaluation technique for bileaflet mechanical valves.

Several techniques were utilized to evaluate the performance of bileaflet mechanical heart valves and improve upon current valve designs. Particle image velocimetry (PIV), computational fluid dynamics (CFD) and video analysis were used to evaluate St. Jude Medical (SJM) and ATS valves in an abrupt enlargement outlet chamber. Video analysis and PIV provided information on the opening angle of the leaflets and 2D velocity fields. PAM-FLOW CFD software was used to predict flow through the valves with leaflets in the fully open position, which corresponds to steady flow conditions in the experimental study. The ATS valve was also modeled at its reported incomplete leaflet opening angle, and with an orifice modification. Additional CFD techniques were employed to find the natural opening angle of the ATS valve. In steady and pulsatile flow, the SJM leaflets opened completely. PIV showed three fairly uniform jets passing through the SJM valve. CFD analysis of the pressure distribution across the SJM valve showed a resultant moment in the open direction, indicating that the leaflets were held against the open stops at 85 degrees. In both steady and pulsatile flow, the leaflets in the ATS valve did not open to the designed opening angle. From video analysis, the ATS leaflet opening angle was estimated at 72-76 degrees. PIV showed that the incomplete opening angle of the ATS leaflets produced a large wake region behind the leaflets, and lateral jets that impinged on the side walls of the test chamber. CFD analysis showed a pressure distribution across the ATS valve which produced a moment causing the leaflets not to open to 85 degrees. The equilibrium position of the leaflet was approximately 75 degrees. The leaflets in the CFD model opened to the full 85 degrees when the orifice was increased by 2 mm on the outflow side. The combination of techniques used in this study provided a method that will be useful in evaluating new valve designs. It was learned that leaflet position, pivot location and orifice height influence pressure distribution across the leaflets, thereby affecting the opening angle.