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

Davis, Kyle (2018-12)

Thesis (MEng)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Artificial heart valves used during valve replacement surgery currently suffer from fatigue (biological valves) or thrombosis (mechanical valves). This study focused on the experimental testing and simulation of a new polyurethane valve (PV tall) based on a previous polyurethane valve design. The new PV tall valve was experimentally evaluated against the original polyurethane design (PV short) and a commercially available tissue valve (tissue), as well as numerically simulated. All three valves were evaluated in a ViVitro Labs pulse duplicator to determine the pressure drop, effective orifice area and percentage regurgitation as required by FDA and ISO regulation. The PV tall valve had a noticeable decrease in the pressure drop and percentage regurgitation compared to the PV short valve, whereas the commercial tissue valve had the lowest values. The effective orifice area of the PV tall valve outperformed the 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 turbulent viscous shear stress (TVSS)was determined to predict the onset of hemolysis and platelet activation. The measured VSS was below the threshold for both platelet activation and hemolysis, however the TVSS predicted that platelet activation could potentially occur for all three valves. The RSSma j value predicted that both platelet activation and hemolysis would occur. The RSSma j and RSS values were found to be subject to manipulation through filtering of large velocity fluctuations, however the VSS and TVSS values did not vary significantly through filtering. A numerical simulation procedure was developed using only open-source software to perform fluid-structure interaction simulations of the newly designed PV tall heart valve. The simulations were performed using openFOAM and CalculiX, and were coupled together using preCICE. The speed and stability of strongly coupled implicit simulations were significantly improved with the use of fast Quasi-Newton coupling schemes compared to conventional Aitken under-relaxation. The simulationswere able to predict the VSS within the fluid domain, after which the wall shear stress (WSS) was obtained from the simulations. The WSS was orders of magnitude larger than the VSS, indicating that theWSS could be amuch larger cause of platelet activation and hemolysis. This study demonstrated the effective use of pulse duplication and particle image velocimetry to experimentally evaluate heart valve hemodynamics. The study also shows that mesh based fluid-structure interaction simulations are capable of providing an early design stage indication of heart valve hemodynamic performance, reducing manufacturing and experimental turn-around times and reducing cost.

AFRIKAANSE OPSOMMING: Kunsmatige hartkleppe wat gedurende klepvervangingchirurgie aangewend word, lei tans aan afmatting (biologies kleppe) of trombose (meganiese kleppe). Hierdie studie fokus op die eksperimentele toetsing en simulasie van ‘n poliuretaanklep (PK lang) wat op ‘n vorige ontwerp gebaseer is. Die nuwe PK langklep is eksperimenteel teen die oorspronklike poliuretaanontwerp (PK kort) en ‘n weefselklep wat kommersiëel beskikbaar is beoordeel. Die drie kleppe is almal volgens die regulasies soos deur die FDA en ISO vereis word in ‘n ViVitro Labs polsduplikator beoordeel om sodoende die drukval, effektiewe openingsarea en herhalingspersentasie te bepaal. Die PK langklep het ‘n merkbare verlaging in die drukval en herhalingspersentasie getoon in vergelyking met die PK kortklep, terwyl die kommersiële weefselklep die laagste waardes getoon het. Die effektiewe openingsarea van die PK langklep het die weefselklep tydens groter kardiale uitsette geklop. Partikelbeeldsnelheidsmetingtoetsing is tydens polsduplikasie op al drie kleppe uitgevoer. Die stroomsnelheidsvektorvelde wat opgelewer is, is ondersoek en die viskose skuif sterkte (VSS), Reynolds skuif sterkte (RSS), hoof Reynolds skuif sterkte (RSShoo f ), en die turbulente viskose skuif sterkte (TVSS) is bepaal om die aanvangs van hemolise en plaatjie-aktivering te voorspel. Die gemete VSS was onder die drempel vir beide plaatjieaktivering en hemolise, hoewel die TVSS voorspel het dat plaatjieaktivering potensiëel vir al drie kleppe kon plaasvind. Die RSShoo f -waarde het voorspel dat beide plaatjieaktivering en hemolise sou plaasvind. Daar is gevind dat beide die RSShoo f - en RSSwaardes aan manipulasie deur filtrering van hewigefluktuasie in snelheid onderhewig is, tog het die VSS- en TVSS-waardes nie beduidend deur filtrering gewissel nie. ‘n Numeriese simulasieprosedure, wat slegs van oopbron sagteware gebruik maak, is ontwikkel ten einde vloeistofstruktuur interaksiesimulasies van die nuut-ontwerpte PV langklep uit te voer. Die simulasies is uitgevoer deur gebruik te maak van openFOAM en CalculiX en is saamgekoppel deur preCICE daarvoor in te span. Die spoed en stabiliteit van sterk-gekoppelde implisiete simulasies is beduidend verbeter deur die gebruik van vinnige Kwasi-Newton koppelingskemas vergeleke met konvensionele Aitken onderontspanning. Die simulasies was daartoe in staat om die VSS binne die vloeistofomgewing te voorspel waarna die wand skuif sterkte (WSS) van die simulasies af verkry is. Die WSS was orde van grootte meer as die VSS, wat aangedui het dat die WSS ‘n baie groter oorsaak van plaatjieaktivering en hemolise kan wees. Hierdie studie demonstreer die effektiewe gebruik van polsduplikasie en partikelbeeldsnelheidsmeting om hartklephemodinamika eksperimenteel te evalueer. Die studie wys ook verder dat stofdigtheidsgebaseerde vloeistofstruktuurinteraksie simulasies daartoe in staat is om in ‘n vroeë ontwerpstadium ‘n aanduiding te gee van hemodinamiese hartklepprestasie, wat vervaardigings- en eksperimentele omdraaitye asook koste verminder.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105077
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