Flow visualization through two types of aortic prosthetic heart valves using stereoscopic high-speed particle image velocimetry.

The number of candidates waiting for a heart valve replacement rises yearly. Even though there is a trend toward implantation of biological valves or reconstruction, the prosthetic heart valves (PHVs) are still commonly used for implantation or as a part of cardiac assist devices in many countries worldwide. However, the hemodynamic consequences of these valves are still not completely understood. Unfortunately, these devices currently do not perform sufficiently on a long-term basis and may lead to several complications, many of them are related to fluid mechanical aspects. A novel method, stereoscopic high-speed particle image velocimetry, was applied to quantify all three velocity components behind a PHV in detailed time domain. In this study, we compared clinically used bileaflet aortic prosthetic (ATS) valve and monoleaflet prototype of tilting disk PHV. The absolute velocities calculated out of two and three velocity components were compared to each other to estimate the overall difference in the desired region of interest. The most significant discrepancies between the two- and three-component absolute velocities were found at the regions of Valsalva sinuses and in a major jet stream of monoleaflet PHV.

Particle image velocimetry-validated, computational fluid dynamics-based design to reduce shear stress and residence time in central venous hemodialysis catheters.

As crucial factors in blood clot formation, shear stress distribution and low flow zones are assessed in different central venous catheter tip designs by using a combined numeric and experimental approach. Computational Fluid Dynamics was validated with Particle Image Velocimetry by comparing simulated and measured velocities and shear strains in three designs of the blood withdrawing arterial lumen: cylindrical and with tip (1) cut straight, (2) cut at an angle, or (3) cut straight with a sleeve entrance. After validation, four additional designs were studied: (4) with two side holes and tip cut straight or (5) at an angle, (6) concentric lumens, and (7) Ash Split-based. In these seven designs, shear stress (SS), blood residence time (RT), and Platelet Lysis Index, which combines the influence of shear stress magnitude and exposure time, were simulated. Concentric catheter was discarded due to highly elevated SS. Ash Split-based design had elevated RT values in the distal tip zone as major inflow occurs through the most proximal side holes, but this is compensated by low average SS. A straight-cut tip and possibly two side holes are preferred when aiming at minimal SS and RT. These data may lead to more patent catheters.