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EVALUATION OF FLOW DYNAMICS THROUGH AN ADJUSTABLE SYSTEMIC-PULMONARY ARTERY SHUNT

OF THESIS EVALUATION OF FLOW DYNAMICS THROUGH AN ADJUSTABLE SYSTEMIC-PULMONARY ARTERY SHUNT An adjustable systemic-pulmonary artery (SPA) shunt is being developed that consists of a polytetrafluoroethylene (PTFE) graft with a screw plunger mechanism. This device would allow full control of flow through SPA shunts used to augment pulmonary blood flow in neonates born with single ventricle physiology. The objective of this study is to evaluate the changes this mechanism has on flow fields for a 4 mm and 5 mm adjustable SPA shunt. Two in vitro models were examined; an idealized model with an axisymmetric constriction and a model developed from 3-D reconstruction of the actual shunt under asymmetric constriction. These models were used to measure the instantaneous velocity and vorticity fields using Particle Image Velocimetry (PIV) under both steady and pulsatile flow conditions. Recirculation regions and maximum values of velocity, vorticity, and shear stress are compared between the 4 mm and 5 mm models. The results indicate that for the idealized model of both shunts, separation regions are much smaller, persisting for approximately 0-1.75 diameters downstream of the constriction, while for the realistic models separation regions of 2.5 diameters downstream were observed. Additional models of a 4 mm and 5 mm shunt were tested under pulsatile conditions matching Re of 1061 and 849 and a Womersley number of 4.09 and 5.12, respectively, as seen in vivo. The maximum shear rates observed in both shunts are within an allowable range without inducing platelet aggregation or hemolysis. However, regions of reverse flow exist distal to the throat, leading to possible concerns of plaque formation. Further in vivo testing will be needed to address this concern. This work is part of an extensive effort in developing a completely implantable adjustable systemic-pulmonary artery shunt.