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The NeoVAD is a proposed paediatric axial-flow Left Ventricular Assist Device (LVAD), small enough to be implanted in infants. The design of the impeller and diffuser blades is important for hydrodynamic performance and haemocompatibility of the pump. This study aimed to optimise the blades for pump efficiency using Computational Fluid Dynamics (CFD), machine learning and global optimisation. Meshing of each design typically included 6 million hexahedral elements and a Shear Stress Transport turbulence model was used to close the Reynolds Averaged Navier–Stokes equations. CFD models of 32 base geometries, operating at 8 flow rates between 0.5 and 4 L/min, were created to match experimental studies. These were validated by comparison of the pressure-flow and efficiency-flow curves with those experimentally measured for all base prototype pumps. A surrogate model was required to allow the optimisation routine to conduct an efficient search; a multi-linear regression, Gaussian Process Regression and a Bayesian Regularised Artificial Neural Network predicted the optimisation objective at design points not explicitly simulated. A Genetic Algorithm was used to search for an optimal design. The optimised design offered a 5.51% increase in efficiency at design point (a 20.9% performance increase) as compared to the best performing pump from the 32 base designs. An optimisation method for the blade design of LVADs has been shown to work for a single objective function and future work will consider multi-objective optimisation. [ABSTRACT FROM AUTHOR]

For those suffering from end-stage biventricular heart failure, and where a heart transplantation is not a viable option, a Total Artificial Heart (TAH) can be used as a bridge to transplant device. The Realheart TAH is a four-chamber artificial heart that uses a positive-displacement pumping technique mimicking the native heart to produce pulsatile flow governed by a pair of bileaflet mechanical heart valves. The aim of this work was to create a method for simulating haemodynamics in positive-displacement blood pumps, using computational fluid dynamics with fluid–structure interaction to eliminate the need for pre-existing in vitro valve motion data, and then use it to investigate the performance of the Realheart TAH across a range of operating conditions. The device was simulated in Ansys Fluent for five cycles at pumping rates of 60, 80, 100 and 120 bpm and at stroke lengths of 19, 21, 23 and 25 mm. The moving components of the device were discretised using an overset meshing approach, a novel blended weak–strong coupling algorithm was used between fluid and structural solvers, and a custom variable time stepping scheme was used to maximise computational efficiency and accuracy. A two-element Windkessel model approximated a physiological pressure response at the outlet. The transient outflow volume flow rate and pressure results were compared against in vitro experiments using a hybrid cardiovascular simulator and showed good agreement, with maximum root mean square errors of 15% and 5% for the flow rates and pressures respectively. Ventricular washout was simulated and showed an increase as cardiac output increased, with a maximum value of 89% after four cycles at 120 bpm 25 mm. Shear stress distribution over time was also measured, showing that no more than 4.5 × 10 - 4 % of the total volume exceeded 150 Pa at a cardiac output of 7 L/min. This study showed this model to be both accurate and robust across a wide range of operating points, and will enable fast and effective future studies to be undertaken on current and future generations of the Realheart TAH. [ABSTRACT FROM AUTHOR]

Background: Patients with end‐stage, biventricular heart failure, and for whom heart transplantation is not an option, may be given a Total Artificial Heart (TAH). The Realheart® is a novel TAH which pumps blood by mimicking the native heart with translation of an atrioventricular plane. The aim of this work was to create a strategy for using Computational Fluid Dynamics (CFD) to simulate haemodynamics in the Realheart®, including motion of the atrioventricular plane and valves. Methods: The accuracies of four different computational methods for simulating fluid‐structure interaction of the prosthetic valves were assessed by comparison of chamber pressures and flow rates with experimental measurements. The four strategies were: prescribed motion of valves opening and closing at the atrioventricular plane extrema; simulation of fluid‐structure interaction of both valves; prescribed motion of the mitral valve with simulation of fluid‐structure interaction of the aortic valve; motion of both valves prescribed from video analysis of experiments. Results: The most accurate strategy (error in ventricular pressure of 6%, error in flow rate of 5%) used video‐prescribed motion. With the Realheart operating at 80 bpm, the power consumption was 1.03 W, maximum shear stress was 15 Pa, and washout of the ventricle chamber after 4 cycles was 87%. Conclusions: This study, the first CFD analysis of this novel TAH, demonstrates that good agreement between computational and experimental data can be achieved. This method will therefore enable future optimisation of the geometry and motion of the Realheart®. [ABSTRACT FROM AUTHOR]

With the recent advances in computer technology, computational fluid dynamics ( CFDs) has become an important tool to design and improve blood-contacting artificial organs, and to study the device-induced blood damage. Commercial CFD software packages are readily available, and multiple CFD models are provided by CFD software developers. However, the best approach of using CFD effectively to characterize fluid flow and to predict blood damage in these medical devices remains debatable. This study aimed to compare these CFD models and provide useful information on the accuracy of each model in modeling blood flow in circulatory assist devices. The laminar and five turbulence models (Spalart-Allmaras, k-ε (k-epsilon), k-ω (k-omega), SST [Menter's Shear Stress Transport], and Reynolds Stress) were implemented to predict blood flow in a clinically used circulatory assist device, the Centri Mag centrifugal blood pump. In parallel, a transparent replica of the Centri Mag pump was constructed and selected views of the flow fields were measured with digital particle image velocimetry ( DPIV). CFD results were compared with the DPIV experimental results. Compared with the experiment, all the selected CFD models predicted the flow pattern fairly well except the area of the outlet. However, quantitatively, the laminar model results were the most deviated from the experimental data. On the other hand, k-ε renormalization group theory models and Reynolds Stress model are the most accurate. In conclusion, for the circulatory assist devices, turbulence models provide more accurate results than the laminar model. Among the selected turbulence models, k-ε and Reynolds Stress Method models are recommended. [ABSTRACT FROM AUTHOR]

Mechanical ventilation and extracorporeal membrane oxygenation are the only immediate options available for patients with respiratory failure. However, these options present significant shortcomings. To address this unmet need for respiratory support, innovative respiratory assist devices are being developed. In this study, we present the computational model-based design, and analysis of functional characteristics and hemocompatibility performance, of an innovative wearable artificial pump-lung (APL) for ambulatory respiratory support. Computer-aided design and computational fluid dynamics (CFD)-based modeling were utilized to generate the geometrical model and to acquire the fluid flow field, gas transfer, and blood damage potential. With the knowledge of flow field, gas transfer, and blood damage potential through the whole device, design parameters were adjusted to achieve the desired specifications based on the concept of virtual prototyping using the computational modeling in conjunction with consideration of the constraints on fabrication processes and materials. Based on the results of the CFD design and analysis, the physical model of the wearable APL was fabricated. Computationally predicted hydrodynamic pumping function, gas transfer, and blood damage potential were compared with experimental data from in vitro evaluation of the wearable APL. The hydrodynamic performance, oxygen transfer, and blood damage potential predicted with computational modeling, along with the in vitro experimental data, indicated that this APL meets the design specifications for respiratory support with excellent biocompatibility at the targeted operating condition. [ABSTRACT FROM AUTHOR]

Abstract: Progress in the field of prosthetic cardiovascular devices has significantly contributed to the rapid advancements in cardiac therapy during the last four decades. The concept of mechanical circulatory assistance was established with the first successful clinical use of heart–lung machines for cardiopulmonary bypass. Since then a variety of devices have been developed to replace or assist diseased components of the cardiovascular system. Ventricular assist devices (VADs) are basically mechanical pumps designed to augment or replace the function of one or more chambers of the failing heart. Computational Fluid Dynamics (CFD) is an attractive tool in the development process of VADs, allowing numerous different designs to be characterized for their functional performance virtually, for a wide range of operating conditions, without the physical device being fabricated. However, VADs operate in a flow regime which is traditionally difficult to simulate; the transitional region at the boundary of laminar and turbulent flow. Hence different methods have been used and the best approach is debatable. In addition to these fundamental fluid dynamic issues, blood consists of biological cells. Device-induced biological complications are a serious consequence of VAD use. The complications include blood damage (haemolysis, blood cell activation), thrombosis and emboli. Patients are required to take anticoagulation medication constantly which may cause bleeding. Despite many efforts blood damage models have still not been implemented satisfactorily into numerical analysis of VADs, which severely undermines the full potential of CFD. This paper reviews the current state of the art CFD for analysis of blood pumps, including a practical critical review of the studies to date, which should help device designers choose the most appropriate methods; a summary of blood damage models and the difficulties in implementing them into CFD; and current gaps in knowledge and areas for future work. [Copyright &y& Elsevier]

The Levitronix UltraMag blood pump is a next generation, magnetically suspended centrifugal pump and is designed to provide circulatory support for pediatric and adult patients. The aim of this study is to investigate the hemodynamic and hemolytic characteristics of this pump using the computational fluid dynamics (CFD) approach. The computational domain for CFD analysis was constructed from the three-dimensional geometry (3D) of the UltraMag blood pump and meshed into 3D tetrahedral/hybrid elements. The governing equations of fluid flow were computationally solved to obtain a blood flow through the blood pump. Further, hemolytic blood damage was calculated by solving a scalar transport equation where the scalar variable and the source term were obtained utilizing an empirical power-law correlation between the fluid dynamic variables and hemolysis. To obtain mesh independent flow solution, a comparative examination of vector fields, hydrodynamic performance, and hemolysis predictions were carried out. Different sizes of tetrahedral and tetrahedral/hexahedral mixed hybrid models were considered. The mesh independent solutions were obtained by a hybrid model. Laminar and SST κ-ω turbulence flow models were used for different operating conditions. In order to pinpoint the most significant hemolytic region, the flow field analysis was coupled to the hemolysis predictions. In summary, computational characterization of the device was satisfactorily carried out within the targeted operating conditions of the device, and it was observed that the UltraMag blood pump can be safely operated for its intended use to create a circulatory support for both pediatric and adult-sized patients. [ABSTRACT FROM AUTHOR]

The goal of this study is to develop a computational fluid dynamics (CFD) modeling approach to better estimate the blood flow dynamics in the bundles of the hollow fiber membrane based medical devices (i.e., blood oxygenators, artificial lungs, and hemodialyzers). Three representative types of arrays, square, diagonal, and random with the porosity value of 0.55, were studied. In addition, a 3D array with the same porosity was studied. The flow fields between the individual fibers in these arrays at selected Reynolds numbers (Re) were simulated with CFD modeling. Hemolysis is not significant in the fiber bundles but the platelet activation may be essential. For each type of array, the average wall shear stress is linearly proportional to the Re. For the same Re but different arrays, the average wall shear stress also exhibits a linear dependency on the pressure difference across arrays, while Darcy's law prescribes a power-law relationship, therefore, underestimating the shear stress level. For the same Re, the average wall shear stress of the diagonal array is approximately 3.1, 1.8, and 2.0 times larger than that of the square, random, and 3D arrays, respectively. A coefficient C is suggested to correlate the CFD predicted data with the analytical solution, and C is 1.16, 1.51, and 2.05.fOr the square, random, and diagonal arrays in this paper', respectively. It is worth noting that C is strongly dependent on the array geometrical properties, whereas it is weakly dependent on the flow field. Additionally, the 3D fiber bundle simulation results show that the three-dimensional effect is not negligible. Specifically, velocity and shear stress distribution can vary significantly along the fiber axial direction. [ABSTRACT FROM AUTHOR]