Finding Optimal Hemo-Compatible Operating Conditions for Ventricular Assistance Device
Authors: Marcel Louis , Specklin Mathieu , Kouidri Smaine 
Published: September 2023

Abstract
Statistics show that since the beginning of the 2000s, a concerning number of patients are diagnosed with Heart Failure (HF) and this number increases steadily. It would not be such an issue if the number of potential heart donors followed the same trend. However, it is not the case resulting in an issue on the number of lives which can be saved. Sometimes, saving some time can be a life savior for these patients on the active waiting list for transplant. It is in this context that the use of Mechanical Circulatory Support (MCS) has proven its efficiency and still has a lot to offer on a longer-term use, to replace one day heart transplant. Today’s MCSs are mostly centrifugal pumps, and the scientific knowledge of their internal flow has been widened using Computational Fluid Dynamics (CFD). Numerical simulations are a way to predict a pump’s internal flow topology, gather information inaccessible by the means of experiment such as local information of the flow and understand its behavior without having to test it experimentally. Before manufacturing an entire device, it appears useful to estimate a certain number of variables related to the flow specificity such as the forces exerted on the structure or on fluid particles. In the specific case of MCS, the number of red blood cells destroyed, depending on the flow topology is estimated by introducing a new variable, the Hemolysis Index (HI). Hemolysis is a natural phenomenon during which red-blood cells degrade themselves and are destroyed after a certain amount of time. The use of rotodynamic devices may accentuate hemolysis, up to a point where the body is unable to produce enough red-blood cells. As a result, these cells won’t be able to provide oxygen to the organs, including to the heart, an already failing organ. The blood being a well-known shear-thinning fluid composed of living cells whose features are essential to the patient’s survival, CFD calculations are crucial before animal testing in order to prevent an accident.
In this study, numerical assessments of hemodynamic parameters of a complex centrifugal Ventricular Assistance Device (VAD) were performed using the Eulerian method. These acquisitions allowed to determine the behavior of these variable under different rotational speed or flow rate, hence leading us to a potential optimal operating point to prevent hemolysis issues. The variations of Hemolysis with rotational speed are predictable, however its variation with flowrate is more complex. Results of this study suggests that the evolution of this variable with flowrate depends on the geometry of the device and that very different results may be observed from a device to another. The global architecture of the device defines specific evolution according to flowrate of mean residential time of fluid particles in the pump or averaged shear stress. The ability of the device to generate more shear stress with an increased flow rate will define the existence of an optimal hemo-compatible operating condition.