Exemplary cases: Total Artificial Heart
For blood pumps with long term indication, blood stagnation can result in excessive thromboembolic risks for the patient. Therefore, a numerical washout model was developed which makes it possible to quantitatively compare different configurations and designs of blood-carrying implants regarding the potential for blood stagnation where experimental measurements are limited.
To evaluate the washout efficiency of a pulsatile Total Artificial Heart (TAH), a Fluid-Structure Interaction (FSI) simulation of the artificial heart pumping process was combined with the blood washout model. The interactions of the pusher plate, the membrane and the blood flow in the pump chamber were considered by performing partitioned block-Gauss–Seidel implicit coupling. In order to achieve numerical stability, a combined resistance and pressure outlet boundary condition as well as the interface artificial compressibility method was applied. Due to the large deformation of the fluid domain, a variable mesh stiffness depending on certain mesh properties was specified for the fluid elements. To make the simulation feasible for engineering design optimization the valve motion could not be considered. Instead, a switching opened/closed boundary condition was applied. To verify the validly of this assumption, the resulting flow field was compared against Particle Image Velocity (PIV) measurements.
By using the approach, four different orientations (0°, 45°, 90° and 135°) of the mitral Mechanical Heart Valve were investigated with respect to blood stagnation (Figure). Nearly complete washout could be achieved after three pump cycles. Remains of old blood in relation to the chamber volume was below 0.6% for all configurations and were mainly detected in the peripheral area opposite the inlet and outlet port at the edge of the membrane and housing connection. A 0° orientation showed minor benefits, however, only little variation of the washout and the flow dynamics could be observed.
This work was funded by the Eurpean Union (EU), the German Federal State of North Rhine-Westphalia and the Erich and Hanna Klessmann Foundation.
Sonntag SJ, Kaufmann TAS, Buesen MR, Laumen M, Linde T, Schmitz-Rode T, Steinseifer U. Simulation of a pulsatile total artificial heart: Development of a partitioned Fluid Structure Interaction model; J. Fluid. Struct. 2013; 38:187-204, DOI: 10.1016/j.jfluidstructs.2012.11.011
Sonntag SJ, Kaufmann TAS, Buesen MR, Laumen M, Gräf F, Linde T, Steinseifer U. Numerical washout study of a pulsatile Total Artificial Heart; Int. J. Artif. Organs 2014; DOI: 10.5301/ijao.5000306