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

Aim To study using computer simulation the effect of irrigant flow rate on the flow pattern within a prepared root canal, during final irrigation with a syringe and needle.



Methodology  Geometrical characteristics of a side-vented endodontic needle and clinically realistic flow rate values were obtained from previous and preliminary studies. A Computational Fluid Dynamics (CFD) model was created using FLUENT 6.2 software. Calculations were carried out for five selected flow rates (0.02–0.79 mL sec−1) and velocity and turbulence quantities along the domain were evaluated.



Results  Irrigant replacement was limited to 1–1.5 mm apical to the needle tip for all flow rates tested. Low-Reynolds number turbulent flow was detected near the needle outlet. Irrigant flow rate affected significantly the flow pattern within the root canal.



Conclusions  Irrigation needles should be placed to within 1 mm from working length to ensure fluid exchange. Turbulent flow of irrigant leads to more efficient irrigant replacement. CFD represents a powerful tool for the study of irrigation.

http://www.endoexperience.com/documents/Boutsioukis-ComutationalFluidDynamics.pdf

Irrigant flow within a prepared root canal using various flow rates: a Computational Fluid Dynamics study

Hemolysis caused by flow-induced mechanical damage to red blood cells is still a problem in medical devices such as ventricular assist devices (VADs), artificial lungs, and mechanical heart valves. A number of different models have been proposed by different research groups for calculating the hemolysis, and of these, the power law-based models (HI(%)=Ct(α)τ(β)) have proved the most popular because of their ease of use and applicability to a wide range of devices. However, within this power law category of models there are a number of different implementations. The aim of this work was to evaluate different power law-based models by calculating hemolysis in a specifically designed shearing device and a clinical VAD, and comparing the estimated results with experimental measurements of the hemolysis in these two devices. Both the Eulerian scalar transport and all the Lagrangian models had fairly large percentage of errors compared with the experiments (minimum Eulerian 91% and minimum Lagrangian 57%) showing they could not accurately predict the magnitude of the hemolysis. However, the Eulerian approach had large correlation coefficients (>0.99) showing that this method can predict relative hemolysis, which would be useful in comparative analysis, for example, for ranking different devices or for design optimization studies.

Evaluation of Eulerian and Lagrangian models for hemolysis estimation.

Implantable left ventricular assist devices (LVADs) became the therapy of choice in treating end-stage heart failure. Although survival improved substantially and is similar in currently clinically implanted LVADs HeartMate II (HM II) and HeartWare HVAD, complications related to blood trauma are frequently observed. The aim of this study was to compare these two pumps regarding their potential blood trauma employing computational fluid dynamics. High-resolution structured grids were generated for the pumps. Newtonian flow was calculated, solving Reynolds-averaged Navier-Stokes equations with a sliding mesh approach and a k-ω shear stress transport turbulence model for the operating point of 4.5 L/min and 80 mm Hg. The pumps were compared in terms of volumes subjected to certain viscous shear stress thresholds, below which no trauma was assumed (von Willebrand factor cleavage: 9 Pa, platelet activation: 50 Pa, and hemolysis: 150 Pa), and associated residence times. Additionally, a hemolysis index was calculated based on a Eulerian transport approach. Twenty-two percent of larger volumes above 9 Pa were observed in the HVAD; above 50 Pa and 150 Pa the differences between the two pumps were marginal. Residence times were higher in the HVAD for all thresholds. The hemolysis index was almost equal for the HM II and HVAD. Besides the gap regions in both pumps, the inlet regions of the rotor and diffuser blades have a high hemolysis production in the HM II, whereas in the HVAD, the volute tongue is an additional site for hemolysis production. Thus, in this study, the comparison of the HM II and the HVAD using numerical methods indicated an overall similar tendency to blood trauma in both pumps. However, influences of turbulent shear stresses were not considered and effects of the pivot bearing in the HM II were not taken into account. Further in vitro investigations are required.

Numerical Analysis of Blood Damage Potential of the HeartMate II and HeartWare HVAD Rotary Blood Pumps.

Ventricular Assist Devices (VADs) provide long- and short-term support to chronically-ill heart disease patients; these devices are expected to match the remarkable functionality of the natural heart, which makes their design a very challenging task. Blood pumps, the principal component of the VADs, must operate over a wide range of flowrates and pressure heads, and minimize the damage to blood cells in the process. They should also be small to allow easy implantation in both children and adults. Mathematical methods and Computational Fluid Dynamics (CFD) have recently emerged as a powerful design tool in this context; a review of the recent advances in the field is presented here. This review focuses on the CFD-based design strategies applied to blood flow in blood pumps and other blood-handling devices. Both simulation methods for blood flow and blood damage models are reviewed. The literature is put into context with a discussion of the chronological development in the field. The review is illustrated with specific examples drawn from our group’s Galerkin/LeastSquares (GLS) finite element simulations of the basic Newtonian flow problem for the continuous-flow centrifugal GYRO blood pump. The GLS formulation is outlined, and modifications to include models that better represent blood rheology are shown. Hemocompatibility analysis of the pump is reviewed in the context of hemolysis estimations based on different blood damage models. Our strainbased blood damage model that accounts for the viscoleasticity associated with the red blood cells is reviewed in detail. The viability of trial-and-error based design improvement and complete simulation-based design optimization schemes are also discussed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0956792509007839

A review of computational fluid dynamics analysis of blood pumps

A major part of developing rotary blood pumps requires the optimization of hemolytic properties of the entire pump. Application of a suited computational fluid dynamics (CFD)-based hemolysis model allows approximation of blood damage in an early phase of the design process. Thus, a drastic reduction of time- and cost- intensive hemolysis experiments can be achieved. For the MicroDiagonal Pump (MDP), still under development at Helmholtz-Institute in Aachen, Germany, different pump configurations have been analyzed, both numerically and experimentally. The CFD model of the pump has been successfully validated based on the comparison of the pressure head curves (H-Q curves), as discussed in a prior publication. In the present study, the authors focus on the development of a semiempiric blood damage model using the CFD and in vitro hemolysis data. On the one hand, mean key characteristics (shear stress and exposure time) and other characteristics affecting blood damage have been calculated based on numerical data. On the other hand, in vitro hemolysis tests have been accomplished in order to determine the hemolytic curves of two different pump configurations (with the same impeller but different tip clearances). Finally, a new function based on a general power law has been defined by means of the mean key characteristics. The unknown constants of the function have been determined by multidimensional regression analysis using the hemolytic curves. For the final validation of this new blood damage model, the calculated and the in vitro obtained hemolysis indices at the specific VAD operating point have been compared for all pump configurations. The comparison showed an excellent agreement, both qualitatively and quantitatively.

A validated computational fluid dynamics model to estimate hemolysis in a rotary blood pump.

The DeltaStream blood pump has been developed for extracorporeal circulation with one focus on potential integration into simplified bypass systems (SBS). Its small size and an embedded electric motor are the basic pump properties. A variation of the impeller design has been performed to optimize hydraulic and hematologic characteristics. A simple impeller design was developed which allows flow and pressure generation for cardiopulmonary bypass applications. The option of a pulsatile flow mode for ventricular assist device applications also was demonstrated in vitro. Impeller washout holes were implemented to improve nonthrombogenicity. The pump was investigated for potential thermal hazards for blood caused by the integrated electric motor. It could be demonstrated that there is no thermal risk associated with this design. Durability tests were performed to assess the lifetime of the pump especially with regard to the incorporated polymeric seal. Seal lifetimes of up to 28 days were achieved using different blood substitutes. In animal tests using either the pump as a single device or in an SBS setup, biocompatibility, low hemolysis, and nonthrombogenicity were demonstrated. In summary, the DeltaStream pump shows great potential for different extracorporeal perfusion applications. Besides heart-lung machine and SBS applications, ventricular assist and extracorporeal membrane oxygenation up to several days also appear promising as potential applications.

Development of the MEDOS/HIA DeltaStream extracorporeal rotary blood pump.

A mixed-flow blood pump for long-term applications has been developed at the Helmholtz-Institute in Aachen, Germany. Central features of this implantable pump are a centrally integrated motor, a blood-immersed mechanical bearing, magnetic coupling of the impeller, and a shrouded impeller, which allows a relatively wide clearance. The aim of the study was a numerical analysis of hydraulic and hemolytic properties of different impeller design configurations. In vitro testing and numerical simulation techniques (computational fluid dynamics [CFD]) were applied to achieve a comprehensive overview. Pressure-flow charts were experimentally measured in a mock loop in order to validate the CFD data. In vitro hemolysis tests were performed at the main operating point of each impeller design. General flow patterns, pressure-flow charts, secondary flow rates, torque, and axial forces on the impeller were calculated by means of CFD. Furthermore, based on streak line techniques, shear stress (stress loading), exposure times, and volume percentage with critical stress loading have been determined. Comparison of CFD data with pressure head measurements showed excel-lent agreement. Also, impressive trend conformity was observed between in-vitro hemolysis results and numerical data. Comparison of design variations yielded clear trends and results. Design C revealed the best hydraulic and hemolytic properties and was chosen as the final design for the mixed-flow rotary blood pump.

Comparison of Hydraulic and Hemolytic Properties of Different Impeller Designs of an Implantable Rotary Blood Pump by Computational Fluid Dynamics

Today, rotary pumps are routinely used for extracorporeal circulation in different clinical settings and applications. A review of these applications and specific limitations in extracorporeal perf...

A new rotary blood pump for versatile extracorporeal circulation: the DeltaStream.

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Papers

A validated computational fluid dynamics model to estimate hemolysis in a rotary blood pump.

Development of the MEDOS/HIA DeltaStream extracorporeal rotary blood pump.

Comparison of Hydraulic and Hemolytic Properties of Different Impeller Designs of an Implantable Rotary Blood Pump by Computational Fluid Dynamics

A new rotary blood pump for versatile extracorporeal circulation: the DeltaStream.