Design and Transient Computational Fluid Dynamics Study of a Continuous Axial Flow Ventricular Assist Device

Abstract

A ventricular assist device (VAD), which is a miniaturized axial flow pump from the point of view of mechanism, has been designed and studied in this report. It consists of an inducer, an impeller, and a diffuser. The main design objective of this VAD is to produce an axial pump with a streamlined, idealized, and nonobstructing blood flow path. The magnetic bearings are adapted so that the impeller is completely magnetically levitated. The VAD operates under transient conditions because of the spinning movement of the impeller and the pulsatile inlet flow rate. The design method, procedure, and iterations are presented. The VAD's performance under transient conditions is investigated by means of computational fluid dynamics (CFD). Two reference frames, rotational and stationary, are implemented in the CFD simulations. The inlet and outlet surfaces of the impeller, which are connected to the inducer and diffuser respectively, are allowed to rotate and slide during the calculation to simulate the realistic spinning motion of the impeller. The flow head curves are determined, and the variation of pressure distribution during a cardiac cycle (including systole and diastole) is given. The axial oscillation of impeller is also estimated for the magnetic bearing design. The transient CFD simulation, which requires more computer resources and calculation efforts than the steady simulation, provides a range rather than only a point for the VAD's performance. Because of pulsatile flow phenomena and virtual spinning movement of the impeller, the transient simulation, which is realistically correlated with the in vivo implant scenarios of a VAD, is essential to ensure an effective and reliable VAD design.

Haemolysis in patients with ventricular assist devices: major differences between systems☆

“…In comparison, the Thoratec BVAD consists of two pneumatic pump systems with mechanical valves. Analysis of blood flow and shear stress obtained by computer simulations [24] and magnetic resonance (MR) analysis [25] could contribute to design less aggressive biventricular support systems.…”

The use of computational fluid dynamics in the development of ventricular assist devices

“…The implementations of these CFD packages are either based on the finite volume23 method or finite element method. Fluent 36, 37, 38, 39, 40, 41 and CFX 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 11, 57, 58, 59, both available from ANSYS, Inc. (Canonsburg, PA) and STAR-CD from CD-Adapco 60, 61 (Melville, New York) are the CFD software packages used most often for analysis and modelling of blood flow in VADs. In addition, AcuSolve from ACUSIM Software 62 (Mountain View, CA) and Adina from Adina R&D (Watertown, MA) are also used.…”

“…Pumps which have been modelled using the slide mesh approach include Nanyang Technological University’s pump 41 and the Virginia LEV-VAD 50. Song et al 50 performed both steady and transient simulations on the Virginia LEV-VAD and showed that the pressure rise throughout the cardiac cycle varied from 80 to 180 mmHg.…”

“…However, this is not the case. The inertia of the blood results in hysteresis and therefore a closed loop in H-Q space 162, 50, 47. Some groups have looked at the effects of flow pulsatility 47, but since the calculations are far more computationally expensive, these studies are in the minority.…”

Shear-induced platelet receptor shedding by non-physiological high shear stress with short exposure time: Glycoprotein Ibα and glycoprotein VI

“…It has been reported that patients with CF-VADs experienced higher rate of bleeding than those with pulsatile-flow devices although anticoagulation was not different among these two groups of patients. We believe that the increased bleeding risk in patients supported with CF-VADs is associated with the unique high shear stress environment in contemporarily available CF-VADs which has been reported in the literature when compared to pulsatile VADs [10] [13–20]. …”