Haemolytic comparison of two bearing designs for the NeoVAD using coupled 3D-0D computational fluid dynamics-lumped parameter modelling

Background: The NeoVAD is a paediatric LVAD aiming to provide safe, long-term, bridge-to-transplant therapy for infants 5-20 kg. The pump uses axial flow with the rotating impeller powered by a blood washed motor. While the current prototype contains a contact bearing, the impeller will be magnetically levitated in the final design. The aim of this study was to investigate the influence of bearing design on flow and haemolysis in the motor-stator gap.
Methods: Ansys CFX was used for solving the equations of fluid motion with computational fluid dynamics (CFD) and, for pulsatile flow, the 3D CFD model was coupled to a 0D lumped parameter model of the circulation implemented in Matlab Simulink. The flow path geometries with contact and mag-lev bearings were extracted from the CAD, and the NeoVAD was situated in an ellipsoid representative of a paediatric ventricle. The main impeller-diffuser was simulated as a momentum source. Flow rate, shear stress and single pass haemolysis index were calculated for the motor-stator gap and the contribution to the overall NeoVAD haemolysis was estimated.
Results: The bearing design determined the direction of the motor-gap flow: the contact bearing created forward flow while the mag-lev bearing created reverse flow. At 2 l/min motor-gap flows were 3 and 26 ml/min with contact and mag-lev bearings respectively; single pass haemolysis indices for the gap were 0.035 and 0.007 %; and contributions to total NeoVAD HI were estimated as 5.3e-5 and 9.1e-5 %. Pulsatile simulations showed Taylor vortices persisted throughout the cardiac cycle in both bearings.
Conclusions: Although the increased flow rate through the motor-stator gap results in a lower single pass HI for the mag-lev bearing, more of the blood is exposed to this damaging region resulting in very similar contributions to the total haemolysis. Future work will investigate whether the increased flow rate reduces thrombosis risk.