Investigating the impact of non‐Newtonian blood models within a heart pump

Abstract

A detailed computational fluid dynamics (CFD) study of transient, turbulent blood flow through a positive displacement left ventricular assist device is performed. Two common models for non-Newtonian blood flow are compared to the Newtonian model to investigate their impact on predicted levels of shear rate and wall shear stress. Given that both parameters are directly relevant to the evaluation of risk from thrombus and haemolysis, there is a need to assess the sensitivity to modelling non-Newtonian flow effects within a pulsatile turbulent flow, in order to identify levels of uncertainly in CFD. To capture the effects of turbulence, the elliptic blending Reynolds stress model is used in the present study, on account of superior performance of second moment closure schemes previously identified by the present authors. The CFD configuration includes two cyclically rotating valves and a moving pusher plate to periodically vary the chamber volume. An overset mesh algorithm is used for each instance of mesh motion, and a zero gap technique was employed to ensure full valve closure. The left ventricular assist device was operated at a pumping rate of 86 BPM (beats per minute) and a systolic duration of 40% of the pumping cycle, in line with existing experimental data to which comparisons are made. The sensitivity of the variable viscosity models is investigated in terms of mean flow field, levels of turbulence and global shear rate, and a non-dimensional index is used to directly evaluate the impact of non-Newtonian effects. The clinical relevance of the results is reported along with a discussion of modelling uncertainties, observing that the turbulent kinetic energy is generally predicted to be higher in non-Newtonian flow than that observed in Newtonian flow. Copyright © 2016 John Wiley & Sons, Ltd.

Experimental investigation of the effect of non-Newtonian behavior of blood flow in the Fontan circulation

“…In general, the non-Newtonian properties of blood are only apparent at shear rates less than 100 s -1 [3]. However, experimental and numerical models have shown that non-Newtonian behavior has a significant influence in the microvasculature [4] and in a variety of settings where low-shear flow is more prevalent such as in ventricular assist devices and aneuryms [5,6,28]. For example, a laser Doppler velocimetry analysis of flow in a pediatric ventricular assist device demonstrated that using a Newtonian fluid generally overestimated wall shear stress and therefore underestimated areas of low wall shear stress/thrombogenic potential compared to a non-Newtonian fluid [5].…”

“…For example, a laser Doppler velocimetry analysis of flow in a pediatric ventricular assist device demonstrated that using a Newtonian fluid generally overestimated wall shear stress and therefore underestimated areas of low wall shear stress/thrombogenic potential compared to a non-Newtonian fluid [5]. A more recent computational fluid dynamics simulation comparing a Newtonian model with two non-Newtonian models in a similar ventricular assist device showed increased turbulent kinetic energy and a larger area of flow recirculation in the non-Newtonian models [6]. Interestingly, in contrast to the Bachmann study the predicted wall shear stress was similar between the Newtonian and non-Newtonian models; this is potentially explained by the larger size of the device in the latter study.…”

Numerical simulation of centrifugal and hemodynamically levitated LVAD for performance improvement

“…The evolution of computational fluid dynamics (CFD) overcomes the mentioned complications and provides a cost‐effective approach to analyze these devices. Many researchers have utilized the CFD techniques to simulate the blood pump and they found the computational findings are in good agreement with their experimental results. This shows that CFD can be a reliable approach to analyze the blood pumps under different operating conditions with lesser complications, as faced in equivalent experiments.…”

Innovative Modeling Techniques and 3D Printing in Patients with Left Ventricular Assist Devices: A Bridge from Bench to Clinical Practice

“…Hemocompatibility has remained a big area of interest. One recent study looked at the degradation of von Willebrand factor (VWF) in continuous flow LVAD and determined that turbulence remained an important factor in VWF degradation regardless of exposure time with the device [22].…”