Heart Valve Dynamics during the Complete

Cardiac Cycle

Dumont K1, Vierendeels J

2, Segers P

1, Verdonck PR

1

1Hydraulics Laboratory, Institute of Biomedical

Technology, UGent, Belgium 2Department 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.