Heart Valve Dynamics during the Complete Cardiac Cycle Dumont K 1 , Vierendeels J 2 , Segers P 1 , Verdonck PR 1 1 Hydraulics Laboratory, Institute of Biomedical Technology, UGent, Belgium 2 Department of Flow, Heat and Combustion Mechanics, Fluid Mechanics Laboratory, UGent, Belgium Introduction In vitro studies on the Advancing The Standard (ATS) valve (ATS Medical, Minneapolis, MN) have shown that the valve opens to the maximum opening angle when it is placed in a straight conduit, but that the valve leaflets open to a less than maximum opening angle when the valve is placed in a diverging conduit, such as when it is placed in mitral position [1]. Methods We have studied valve leaflet behaviour using a new computational fluid-structure interaction (FSI) model [2,3] making use of Fluent software, extended with dedicated user-defined function to account for the FSI. A three dimensional (3D) model of the ATS valve was studied in 2 geometries, simulating the valve in a straight conduit and a conduit with a sudden expansion downstream of the valve. The velocity profile, used as inflow boundary condition, has a peak velocity of 1 m/s, a period of 2 seconds, with forward flow during 1 second. A. 'straight' geometry B. 'expanding' geometry Figure 1: Studied Geometries of the ATS valve. Figure 2: Boundary Condition : Velocity Inlet. Results In the straight conduit, the ATS valve opens to the maximum opening angle in 0.147 s and remains in that position for 0.702 s. The peak pressure gradient over the valve is 3.5 mmHg. In the expanding conduit, the valve opens to the maximum opening angle but remains in this position only for 0.092 seconds, after which it moves toward a more closed position. The average opening angle is 69.7 degrees. Peak pressure gradient over the valve is 2.8 mmHg. Figure 3: Pathlines at t=0.6s in both geometries, coloured with respect to pressure gradients. Figure 4: Leaflet Excursions and Pressure Gradients in both geometries. Discussion and Conclusion Our numerical study confirms that valve hemodynamics and leaflet excursion depend on the geometrical constraint of the valve: the presence of a diverging flow results in less than maximum opening of the valve leaflets [1] and reduces the peak pressure gradient. The inlet boundary condition was based on a validation study [3]. Although the model has shown its ability of modelling the dynamic behaviour of mechanical heart valves, future work using physiological boundary conditions could lead to more interesting insights. This new FSI model will be a major research tool to unravel the hemodynamics associated with thrombolytic and hemolytic events of existing and new mechanical heart valves. References [1] Feng Z., Umezu M., Fujimoto T., Tsukahara T., Nurishi M. and Kawaguchi D. In vitro hydrodynamic characteristics among three bileaflet valves in the mitral position. Artificial Organs Volume 24 Number 5, 346–354, 2000. [2] Vierendeels, J., Dumont, K. and Verdonck, P. Stabilization of a fluid-structure coupling procedure for rigid body motion. 33rd AIAA Fluid Dynamics Conference and Exhibit AIAA– 2003–3720, 23–26 june 2003, Orlando, US, 2003. [3] Dumont K., Stijnen J., Vierendeels J., van de Vosse F. and Verdonck P. Validation of a fluid-structure interaction model of a heart valve using the dynamic mesh method in fluent. accepted for publication in Computer Methods in Biomechanics and Biomedical Engineering 2004.