An Accelerated Thrombosis Model for Computational Fluid Dynamics Simulations in Rotary Blood Pumps

Purpose Thrombosis ranks among the major complications in blood-carrying medical devices and a better understanding to influence the design related contribution to thrombosis is desirable. Over the past years many computational models of thrombosis have been developed. However, numerically cheap models able to predict localized thrombus risk in complex geometries are still lacking. The aim of the study was to develop and test a computationally efficient model for thrombus risk prediction in rotary blood pumps. Methods We used a two-stage approach to calculate thrombus risk. The first stage involves the computation of velocity and pressure fields by computational fluid dynamic simulations. At the second stage, platelet activation by mechanical and chemical stimuli was determined through species transport with an Eulerian approach. The model was compared with existing clinical data on thrombus deposition within the HeartMate II. Furthermore, an operating point and model parameter sensitivity analysis was performed. Results Our model shows good correlation (R2 > 0.93) with clinical data and identifies the bearing and outlet stator region of the HeartMate II as the location most prone to thrombus formation. The calculation of thrombus risk requires an additional 10–20 core hours of computation time. Conclusion The concentration of activated platelets can be used as a surrogate and computationally low-cost marker to determine potential risk regions of thrombus deposition in a blood pump. Relative comparisons of thrombus risk are possible even considering the intrinsic uncertainty in model parameters and operating conditions.

Evaluation of the efficiency of a new pulsatile flow‑generating circulatory-assist system in rotary blood pumps. Research on a mathematical model

Objective: to study the effect of a pulsatile flow-generation (PFG) device on the basic hemodynamic parameters of the circulatory system using a mathematical model.Results. Modelling and simulation showed that the use of PFG significantly (76%) increases aortic pulse pressure. The proposed mathematical model adequately describes the dynamics of the circulatory system and metabolism (oxygen debt) on physical activity in normal conditions and heart failure, and the use of non-pulsatile and pulsatile circulatory-assist systems. The mathematical model also shows that the use of PFG device blocks the development of rarefaction in the left ventricular cavity associated with a mismatch of blood inflow and outflow in diastolic phase when there is need to increase systemic blood flow by increasing the rotary pump speed.

DESIGN AND DEVELOPMENT OF MINIATURE SLOTTED IMPELLER FOR SAI SPANDAN TOTAL ARTIFICIAL HEART FOR DESTINATION THERAPY

In recent years, the use of rotary blood pumps (RBPs) as continuous ow VADs has surged ahead, and virtually eliminated the use of pulsatile-ow or volume-displacement pumps for implantable, chronic mechanical circulatory support (MCS). Circuit Design modications like that in Saispandan has imparted pulsatility into RBP.Impeller designs are a signicant factor when designing centrifugal pumps as mechanical circulatory assist devices as smaller diameter impellers with higher rotational speeds to achieve target outputs would cause more blood component trauma compared to larger diameter impellers.Hydraulic performance and hemolysis tests in the same pump housing with different prototypes is needed. Ventricular assist parameters for efcient circulatory support would include an output of 5 L/min against 100 mmHg at speeds of 2500-3500 rpm. Vein height does not contribute signicantly to evaluation metric in most studies.

Flow profile generation for a left ventricular assist device using iterative learning control

Nowadays, rotary blood pumps for the treatment of end-stage heart failure patients are usually fixed-speed controlled. Therefore, without sufficient heart activity, patients may reveal reduced blood flow pulsatility. However, there is evidence that pulsatile flow reduces adverse events. Furthermore, optimized pump flow profiles could be used to achieve certain control objectives. Therefore, a pump flow model is identified and subsequently used to design a control system with an iterative learning controller to generate desired pump flow patterns. Either a flow sensor is required for direct measurement or the flow can be estimated from pressure sensor readings using the proposed pump flow model. For comparison, a PID controller with disturbance feedforward control is also designed. Furthermore, the robustness against respiratory sinus arrhythmia is analyzed.

Large eddy simulation as a fast and accurate engineering approach for the simulation of rotary blood pumps

An accurate representation of the flow field in blood pumps is important for the design and optimization of blood pumps. The primary turbulence modeling methods applied to blood pumps have been the Reynolds-averaged Navier–Stokes (RANS) or URANS (unsteady RANS) method. Large eddy simulation (LES) method has been introduced to simulate blood pumps. Nonetheless, LES has not been widely used to assist in the design and optimization of blood pumps to date due to its formidable computational cost. The purpose of this study is to explore the potential of the LES technique as a fast and accurate engineering approach for the simulation of rotary blood pumps. The performance of “Light LES” (using the same time and spatial resolutions as the URANS) and LES in two rotary blood pumps was evaluated by comparing the results with the URANS and extensive experimental results. This study showed that the results of both “Light LES” and LES are superior to URANS, in terms of both performance curves and key flow features. URANS could not predict the flow separation and recirculation in diffusers for both pumps. In contrast, LES is superior to URANS in capturing these flows, performing well for both design and off-design conditions. The differences between the “Light LES” and LES results were relatively small. This study shows that with less computational cost than URANS, “Light LES” can be considered as a cost-effective engineering approach to assist in the design and optimization of rotary blood pumps.

An accelerated thrombosis model for computational fluid dynamics simulations in rotary blood pumps

PurposeThrombosis is one of the major complications in blood-carrying medical devices and a better understanding to influence design of such devices is desirable. Over the past years many computational models of thrombosis have been developed. However, open questions remain about the applicability and implementation within a pump development process. The aim of the study was to develop and test a computationally efficient model for thrombus risk prediction in rotary blood pumps.MethodsWe used a two-stage approach to calculate thrombus risk. At the first stage, the velocity and pressure fields were computed by computational fluid dynamic (CFD) simulations. At the second stage, platelet activation by mechanical and chemical stimuli was determined through species transport with an Eulerian approach. The model was implemented in ANSYS CFX and compared with existing clinical data on thrombus deposition within the HeartMate II.ResultsOur model shows good correlation (R2>0.94) with clinical data and identifies the bearing and outlet stator region of the HeartMate II as the location most prone to thrombus formation. The calculation of platelet activation requires an additional 10-20 core hours of computation time.DiscussionThe concentration of activated platelets can be used as a surrogate marker to determine risk regions of thrombus deposition in a blood pump. Model expansion, e.g. by including more chemical species can easily be performed. We make our model openly available by implementing it for the FDA benchmark blood pump.DeclarationsFundingThis research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Open access funding enabled and organized by Projekt DEAL.Conflict of interestAll of the authors have nothing to disclose.Availability of data and materialThe raw data can be retrieved by request from the authors.Code availabilityThe implementation of the thrombus model in the FDA benchmark blood pump geometry is available on https://doi.org/10.5281/zenodo.5116063.Authors’ contributionsAll authors contributed to the study conception and design. CB developed the numerical model, performed the simulations, gathered, analysed and discussed the results. SGH, MN and US were involved in the analysis and discussion of the results. MN supervised the project. MN and CB wrote the manuscript based on the input of all co-authors. All co-authors read and approved the final version of the manuscript.

The Effect of Blood Viscosity on Shear-Induced Hemolysis using a Magnetically Levitated Shearing Device

Introduction: Blood contacting medical devices, including rotary blood pumps, can cause shear-induced blood damage that may lead to adverse effects in patients. Due in part to an inadequate understanding of how cell-scale fluid mechanics impact red blood cell membrane deformation and damage, there is currently not a uniformly accepted engineering model for predicting blood damage caused by complex flow fields within ventricular assist devices (VADs). Methods: We empirically investigated hemolysis in an axial Couette flow device typical of a rotary VAD to expand our current understanding of shear-induced blood damage in two ways. First, we used a magnetically levitated device to accurately control the shear rate and exposure time experienced by blood and to minimize the effects of other uncharacterized stresses. Second, we explored the effects of both hematocrit and plasma viscosity on shear-induced hemolysis to characterize blood damage based on the viscosity-independent shear rate, rather than on shear stress. Results: Over a shear rate range of 20,000-80,000 1/s, the Index of Hemolysis was found to be largely independent of hematocrit, bulk viscosity, or the suspension media viscosity. Conclusion: It is recommended that future investigations of shear-induced blood damage report findings with respect to the viscosity-neutral term of shear rate, in addition to the bulk whole blood viscosity measured at an appropriate shear rate relevant to the flow conditions of the device.