Stereo High Speed PIV Measurements behind two different Artificial Heart Valves

The flow behind artificial prosthetic heart valves (PHV) is assessed in order to innovate designs for better qualitative and quantitative performance. One of the major problems is still blood damage, due to the interaction with the valve. It is of high clinical importance to optimize shear stresses loading, avoid cavitation and minimize the backflow. Moreover, various heart valve types have different efficiency, beside others, mostly given by the quality of the flow in all regions across the valve. The flow is highly unsteady and turbulent, therefore it is needed to obtain detailed, high resolution, flow field results in order to assess existing or create new PHVs to achieve better valve hemodynamics. Particle Image Velocimetry (PIV) is already a widely accepted experimental technique for visualization of the flow behind the PHVs in even two- dimensional vitro conditions. Extending this promising technique with the latest developed hardware we were able to achieve the 3 rd velocity component in high resolution time scale. Two high speed cameras in a stereo setup allow the measurement of all three velocity components as a function of time. For our study we fixed a PHV into a silicone mock aorta. This aorta was specially designed to mimic the human anatomy and elasticity. A modified, commercially available, Vivitro mock loop was used to simulate the human blood circulatory system. Stereo High Speed Particle Image Velocimetry (SHSPIV) was monitoring the flow 50 mm downstream the valve plane. A Nd:YLF high-repetition-rate double-cavity laser was combined with two high frame rate CMOS cameras getting a detailed acquisition of the time-dependent flow structure behind the valve. The aim was to compare a clinical bileaflet and a prototype of a monoleaflet tilting disc valve. The results confirm the existing of a complex three dimensional mixing flow. Typical three jet streams flow pattern for bileaflet valve is presen, while the flow behind the monoleaflet is more turbulent with one major and one minor jet stream. The measured velocity values of component in z axis are almost three times higher in the monoleaflet compared to the tested valve.