Evaluation of the Impeller Shroud Performance of an Axial Flow Ventricular Assist Device Using Computational Fluid Dynamics

Abstract

Generally, there are two types of impeller design used in the axial flow blood pumps. For the first type, which can be found in most of the axial flow blood pumps, the magnet is embedded inside the impeller hub or blades. For the second type, the magnet is embedded inside the cylindrical impeller shroud, and this design has not only increased the rotating stability of the impeller but has also avoided the flow interaction between the impeller blade tip and the pump casing. Although the axial flow blood pumps with either impeller design have been studied individually, the comparisons between these two designs have not been conducted in the literature. Therefore, in this study, two axial flow blood pumps with and without impeller shrouds were numerically simulated with computational fluid dynamics and compared with each other in terms of hydraulic and hematologic performances. For the ease of comparison, these two models have the same inner components, which include a three-blade straightener, a two-blade impeller, and a three-blade diffuser. The simulation results showed that the model with impeller shroud had a lower static pressure head with a lower hydraulic efficiency than its counterpart. It was also found that the blood had a high possibility to deposit on the impeller shroud inner surface, which greatly enhanced the possibility of thrombus formation. The blood damage indices in both models were around 1%, which was much lower than the 13.1% of the axial flow blood pump of Yano et al. with the corresponding experimental hemolysis of 0.033 g/100 L.

Numerical Analysis of Blood Damage Potential of the HeartMate II and HeartWare HVAD Rotary Blood Pumps

“…One method to provide insight in hemocompatibility is computational fluid dynamics (CFD). CFD has been widely used in the development process of rotary blood pumps: to describe hydrodynamic performance, to optimize pump design as well as to assess potential blood trauma . In that context, Fraser et al.…”

“…One method to provide insight in hemocompatibility is computational fluid dynamics (CFD). CFD has been widely used in the development process of rotary blood pumps: to describe hydrodynamic performance, to optimize pump design as well as to assess potential blood trauma (9)(10)(11). In that context, Fraser et al presented a detailed comparison of numerical blood damage parameters in three implantable axial pumps and two extracorporeal centrifugal pumps (12).…”

Energetics of blood flow in Fontan circulation under VAD support

“…This turbulence model operates as the k ‐ ω model in zones spaced from the walls and as the k ‐ ε model in the near‐wall layers. Due to this fact, the k ‐ ω SST model describes the flow behavior in different pump zones more precisely …”

“…Due to this fact, the k-ω SST model describes the flow behavior in different pump zones more precisely. 26 (1) The average cardiac output for children in the age group up to 5 years is about 2.2 L/min. 27 The average blood flow rate through IVC and SVC is about 63% and 37% of the cardiac output.…”

Flow Visualization in the Outflow Cannula of an Axial Blood Pump

“…Generally, hemolysis is caused by high shear stress and a thrombus is formed in turbulent flow. In an axial blood pump, the most important region is in the pump casing where the flow is extremely complex [8][9][10][11]. However, the outflow cannula area is also highly relevant to thrombus formation because blood coming from the pump casing usually forms stagnant, whirlpool, or spiral flow which may cause a thrombus [12,13].…”