Numerical and experimental investigation of the hemodynamics of an artificial heart valve.

[摘要] ENGLISH ABSTRACT: Artificial heart valves used during valve replacement surgery currently suffer fromfatigue (biological valves) or thrombosis (mechanical valves). This study focused on theexperimental testing and simulation of a new polyurethane valve (PV tall) based on aprevious polyurethane valve design. The new PV tall valve was experimentally evaluatedagainst the original polyurethane design (PV short) and a commercially available tissuevalve (tissue), as well as numerically simulated.All three valves were evaluated in a ViVitro Labs pulse duplicator to determine thepressure drop, effective orifice area and percentage regurgitation as required by FDA andISO regulation. The PV tall valve had a noticeable decrease in the pressure drop and percentageregurgitation compared to the PV short valve, whereas the commercial tissuevalve had the lowest values. The effective orifice area of the PV tall valve outperformedthe tissue valve at larger cardiac outputs.Particle image velocimetry testingwas performed on all three valves during pulse duplication.The obtained velocity vector fields were examined and the viscous shear stress(VSS), Reynolds shear stress (RSS), major Reynolds shear stress (RSSma j ) and turbulentviscous shear stress (TVSS)was determined to predict the onset of hemolysis and plateletactivation. The measured VSS was below the threshold for both platelet activation andhemolysis, however the TVSS predicted that platelet activation could potentially occurfor all three valves. The RSSma j value predicted that both platelet activation and hemolysiswould occur. The RSSma j and RSS values were found to be subject to manipulationthrough filtering of large velocity fluctuations, however the VSS and TVSS values did notvary significantly through filtering.A numerical simulation procedure was developed using only open-source softwareto perform fluid-structure interaction simulations of the newly designed PV tall heart valve. The simulations were performed using openFOAM and CalculiX, and were coupledtogether using preCICE. The speed and stability of strongly coupled implicit simulationswere significantly improved with the use of fast Quasi-Newton coupling schemescompared to conventional Aitken under-relaxation. The simulationswere able to predictthe VSS within the fluid domain, after which the wall shear stress (WSS) was obtainedfrom the simulations. The WSS was orders of magnitude larger than the VSS, indicatingthat theWSS could be amuch larger cause of platelet activation and hemolysis.This study demonstrated the effective use of pulse duplication and particle image velocimetryto experimentally evaluate heart valve hemodynamics. The study also showsthat mesh based fluid-structure interaction simulations are capable of providing an earlydesign stage indication of heart valve hemodynamic performance, reducing manufacturingand experimental turn-around times and reducing cost.

[发布机构] Stellenbosch University