Modeling hemodynamics in an unoccluded and partially occluded inferior vena cava under rest and exercise conditions

Optimizing inferior vena cava filter design: A computational fluid dynamics study on strut configuration for enhanced hemodynamic performance and thrombosis reduction

Background and objective

Inferior vena cava filters have been shown to be effective in preventing deep vein thrombosis and its secondary complication, pulmonary embolism, thereby reducing the high mortality rate. Although inferior vena cava filters have evolved, specific complications like inferior vena cava thrombosis-induced deep vein thrombosis worsening and recurrent pulmonary embolism continue to pose challenges. This study analyzes the effects of geometric parameter variations of inferior vena cava filters, which have a significant impact on the thrombus formation inside the filter, the capture, dissolution, and hemodynamic flow of thrombus, as well as the shear stress on the filter and vascular wall.

Methods

This study used computational fluid dynamic simulations with the carreau model to investigate the impact of varying inferior vena cava filter design parameters (number of struts, strut arm length, and tilt angle) on hemodynamics.

Results

Recirculation and stagnation areas due to flow velocity and pressure, along with wall shear stress values, were identified as key factors. It is important to find a balance between wall shear stress high enough to aid thrombolysis and low enough to prevent platelet activation. The results of this paper show that the risk of platelet activation and thrombus filtration may be lowest when the wall shear stress of the filter ranges from 0 to 4 [Pa], minimizing stress concentration within the filter.

Conclusion

16 arm struts with a length of 20 mm and a tilt angle of 0° provide the best balance between thrombus capture and minimization of hemodynamic disturbance. This configuration minimizes the size of the stagnation and recirculation zones while maintaining sufficient wall shear stress for thrombus dissolution.

Influence of Exercise on Inferior Vena Cava Wall Interaction with Inferior Vena Cava Filters: Results of a Pilot In Vivo Porcine Study

Purpose The aim of this study was to assess the effect of mild exercise on inferior vena cava (IVC) filter interaction with imaging and pathological features with the neighboring vessel wall utilizing a porcine model.

Methods After Institutional Animal Care and Use Committee (IACUC) approval, retrievable Option Elite IVC filters were implanted in six Yorkshire pigs utilizing the right common femoral vein approach under general anesthesia. Group A (n = 4) pigs remained sedentary for 4 weeks. Group B (n = 2) pigs were exercised using a harness and treadmill for 10 minutes/day for 4 days/week. At approximately 4 weeks, IVC venograms were performed and the pigs were sacrificed. After laparotomy, the IVC was ligated above and below the filter, excised and fixed in formalin. Gross and histological examination of the IVC was performed. Gross images of each sample were captured before removal of the filters. One longitudinal, one tangential, and five transverse representative sections were processed for paraffin sectioning and hematoxylin and eosin slides were prepared. A pathologist examined all tissues to assess differences between normal vein, group A and group B pigs. The pathologist provided an overall assessment and representative images.

Results All IVC filter implantations were technically successful without adverse effects. There was no incidence of caval thrombosis, filter strut fracture, or filter migration in either group. On gross pathological examination, IVC of the pigs in group B demonstrated more perivascular and mural fibrosis than those pigs in group A. Histopathological findings correlated with gross findings.

Conclusions In this pilot study, there were no incidence of IVC filter strut fracture, penetration or IVC occlusion in sedentary or exercised pigs. However, there tended to be more perivascular and mural fibrosis on pathological examination of inferior vena cavas from exercised pigs. Further larger scale studies may employ the porcine model to further understand the role exercise may play on IVC filter and caval wall interaction.

Computational evaluation of inferior vena cava filters through computational fluid dynamics methods

Numerical simulation is growing in its importance toward the design, testing and evaluation of medical devices. Computational fluid dynamics and finite element analysis allow improved calculation of stress, heat transfer, and flow to better understand the medical device environment. Current research focuses not only on improving medical devices, but also on improving the computational tools themselves. As methods and computer technology allow for faster simulation times, iterations and trials can be performed faster to collect more data. Given the adverse events associated with long-term inferior vena cava (IVC) filter placement, IVC filter design and device evaluation are of paramount importance. This work reviews computational methods used to develop, test, and improve IVC filters to ultimately serve the needs of the patient.

In Vitro Clot Trapping Efficiency of the FDA Generic Inferior Vena Cava Filter in an Anatomical Model: An Experimental Fluid-Structure Interaction Benchmark

PURPOSE

Robust experimental data for performing validation of fluid-structure interaction (FSI) simulations of the transport of deformable solid bodies in internal flow are currently lacking. This in vitro experimental study characterizes the clot trapping efficiency of a new generic conical-type inferior vena cava (IVC) filter in a rigid anatomical model of the IVC with carefully characterized test conditions, fluid rheological properties, and clot mechanical properties.

METHODS

Various sizes of spherical and cylindrical clots made of synthetic materials (nylon and polyacrylamide gel) and bovine blood are serially injected into the anatomical IVC model under worst-case exercise flow conditions. Clot trapping efficiencies and their uncertainties are then quantified for each combination of clot shape, size, and material.

RESULTS

Experiments reveal the clot trapping efficiency increases with increasing clot diameter and length, with trapping efficiencies ranging from as low as approximately 42% for small 3.2 mm diameter spherical clots up to 100% for larger clot sizes. Because of the asymmetry of the anatomical IVC model, the data also reveal the iliac vein of clot origin influences the clot trapping efficiency, with the trapping efficiency for clots injected into the left iliac vein up to a factor of 7.5 times greater than that for clots injected into the right iliac (trapping efficiencies of approximately 10% versus 75%, respectively).

CONCLUSION

Overall, this data set provides a benchmark for validating simulations predicting IVC filter clot trapping efficiency and, more generally, low-Reynolds number FSI modeling.

Hemodynamic Analysis of VenaTech Convertible Vena Cava Filter Using Computational Fluid Dynamics

The VenaTech convertible filter (VTCF) has been widely used as an inferior vena cava (IVC) filter to prevent fatal pulmonary embolism in patients. However, its hemodynamics that greatly affect the filter efficacy and IVC patency are still unclear. This paper uses computational fluid dynamics with the Carreau model to simulate the non-Newtonian blood flows around the VTCF respectively deployed in the normal, reverse and three converted states in an IVC model. The results show that the prothrombotic stagnation zones are observed downstream from the normal, reverse and small open VTCFs, with the streamwise length is nearly eight times the IVC diameter. The no-slip boundary conditions of the thin-wire VTCF arms lead to the “viscous block” effect. The viscous block accelerates the blood flow by 5–15% inside the IVC and enhances the filter wall shear stress up to nearly 20 times that of the IVC only, which contributes to clot capture and thrombus lysis. The relative flow resistance is defined to evaluate the filter-induced resistance on the IVC blood flow that can be regarded as an index of IVC patency with the filter deployment. The flow resistance of the normal VTCF deployment increases dramatically by more than 60% compared with that of the IVC only and is a little higher (6%) than that of the reverse case. As the VTCF converts to a fully open configuration, the flow resistance gradually decreases to that of no filter. This work shows that even very thin VTCF arms can result in the viscous block effect and may cause significant hemodynamic impacts on clot capture, potential thrombosis and flow impedance inside the IVC. The present study also shows that CFD is a valuable and feasible in silico tool for analyzing the IVC filter hemodynamics to complement in vivo clinical and in vitro experimental studies.

Computational modeling of drug transport and mixing in the chemofilter device: enhancing the removal of chemotherapeutics from circulation

Intra-arterial chemotherapy (IAC) is the preferred treatment for non-resectable hepatocellular carcinoma. A large fraction of IAC drugs, e.g., Doxorubicin, pass into systemic circulation, causing cardiac toxicity and reducing effectiveness of the procedure. These excessive drugs can be captured by the Chemofilter-a 3D-printable, catheter-based device deployed in a vein downstream of the liver during IAC. In this study, alternative configurations of the Chemofilter device were compared by evaluating their hemodynamic and filtration performance through multiphysics computational fluid dynamics simulations. Two designs were evaluated, a honeycomb-like structure of parallel hexagonal channels (honeycomb Chemofilter) and a cubic lattice of struts (strutted Chemofilter). The computationally optimized Chemofilter design contains three honeycomb stages, each perforated and twisted, which improved Doxorubicin adsorption by 44.6% compared to a straight channel design. The multiphysics simulations predicted an overall 66.8% decrease in concentration with a 2.9 mm-Hg pressure drop across the optimized device compared to a 50% concentration decrease observed during in-vivo experiments conducted with the strutted Chemofilter. The Doxorubicin transport simulations demonstrated the effectiveness of the Chemofilter in removing excessive drugs from circulation while minimizing pressure drop and eliminating flow stagnation regions prone to thrombosis. These results demonstrate the value of the multiphysics modeling approach in device optimization and experimental burden reduction.

Hemodynamic effects of blood clots trapped by an inferior vena cava filter

The alteration of blood flow around an OPTEASE inferior vena cava filter with one or two blood clots attached was investigated by means of computational fluid dynamics. We used a patient-specific vein wall geometry, and we generated different clot models with shapes adapted to the filter and vein wall geometries. A total of eight geometries, with one or two clots and a total clot volume of 0.5 or 1 cm³ , were considered. A non-Newtonian model for blood viscosity was adopted and the possible development of turbulence was accounted for by means of a three-equation model. Two blood flow rates were considered for each case, representative for rest and exercise conditions. In exercise conditions, flow unsteadiness and even turbulence was detected in some cases. Pressure and wall shear stress (WSS) distributions were modified in all cases. Clots attached to the filter downstream basket considerably increased averaged WSS values by up to almost 50%. In all the cases a flow recirculation region appeared downstream of the clot. The degree of flow stagnation in these regions, an indicator of propensity to thrombogenesis, was estimated in terms of mean residence times and mean blood viscosity. High levels of flow stagnation were detected in rest conditions in the wake of those clots that were placed upstream from the filter. Our results suggest that one downstream placed big clot, showing a higher tendency to induce flow instabilities and turbulence, might be more harmful than two small clots placed in tandem.

Steady Flow in a Patient-Averaged Inferior Vena Cava-Part I: Particle Image Velocimetry Measurements at Rest and Exercise Conditions

PURPOSE

Although many previous computational fluid dynamics (CFD) studies have investigated the hemodynamics in the inferior vena cava (IVC), few studies have compared computational predictions to experimental data, and only qualitative comparisons have been made. Herein, we provide particle image velocimetry (PIV) measurements of flow in a patient-averaged IVC geometry under idealized conditions typical of those used in the preclinical evaluation of IVC filters.

METHODS

Measurements are acquired under rest and exercise flow rate conditions in an optically transparent model fabricated using 3D printing. To ensure that boundary conditions are well-defined and to make follow-on CFD validation studies more convenient, fully-developed flow is provided at the inlets (i.e., the iliac veins) by extending them with straight rigid tubing longer than the estimated entrance lengths. Velocity measurements are then obtained at the downstream end of the tubing to confirm Poiseuille inflow boundary conditions.

RESULTS

Measurements in the infrarenal IVC reveal that flow profiles are blunter in the sagittal plane (minor axis) than in the coronal plane (major axis). Peak in-plane velocity magnitudes are 4.9 cm/s and 27 cm/s under the rest and exercise conditions, respectively. Flow profiles are less parabolic and exhibit more inflection points at the higher flow rate. Bimodal velocity peaks are also observed in the sagittal plane at the elevated flow condition.

CONCLUSIONS

The IVC geometry, boundary conditions, and infrarenal velocity measurements are provided for download on a free and publicly accessible repository at https://doi.org/10.6084/m9.figshare.7198703 . These data will facilitate future CFD validation studies of idealized, in vitro IVC hemodynamics and of similar laminar flows in vascular geometries.

A two-scale approach for CFD modeling of endovascular Chemofilter device

Two-scale CFD modeling is used to design and optimize a novel endovascular filtration device for removing toxins from flowing blood. The Chemofilter is temporarily deployed in the venous side of a tumor during the intra-arterial chemotherapy in order to filter excessive chemotherapy drugs such as Doxorubicin from the blood stream. The device chemically binds selective drugs to its surface thus filtering them from blood, after they have had the effect on the tumor and before they reach the heart and other organs. The Chemofilter consists of a porous membrane made of microscale architected materials and is installed on a structure similar to an embolic protection device. Simulations resolving the microscale structure of the device were carried out to determine the permeability of the microcell membrane. The resulting permeability coefficients were then used for macroscale simulations of the flow through the device modeled as a porous material. The microscale simulations indicate that greater number of microcell layers and smaller microcell size result in increased pressure drop across the membrane, while providing larger surface area for drug binding. In the macroscale simulations, the study of idealized prototypes show that the pressure drop can be reduced by increasing the membrane's tip angle and by decreasing the number of membrane's sectors. Such design, however, can conversely affect the overall drug binding. By decreasing the concentration of toxins in the cardiovascular system, the drug dosage can be increased while side effects are reduced, thus improving the effectiveness of treatment.

A comparative CFD study of four inferior vena cava filters

Computational fluid dynamics was used to simulate the flow of blood within an inferior vena cava (IVC) geometry model that was reconstructed from computed tomography images obtained from a real patient. The main novelty of the present work is that we simulated the implantation of 4 different filter models in this realistic IVC geometry. We considered different blood flow rates in the range between V_in =20 and V_in =80 cm³ /s, and all simulations were performed with both the Newtonian and a non-Newtonian model for the blood viscosity. We compared the hemodynamics performance of the different filter models, and we paid a special attention to the total drag force, F_d , exerted by the blood flow on the filter surface. This force is the sum of 2 contributions: the viscous skin friction force, which was found to be roughly proportional to the filter surface area, and the pressure force, which depended on the particular filter geometry design. The F_d force is relevant because it must be balanced by the total force exerted by the filter hooks/struts on the IVC wall at the attachment locations. For the highest V_in value investigated, the variation in F_d among filters was from 116 to 308 dyne. We also showed how the present results can be extrapolated to obtain good estimates of the drag forces if the blood viscosity levels change, ie, if the patient with a filter implanted is treated with anticoagulant therapy.

Influence of a Commercial Antithrombotic Filter on the Caval Blood Flow During Neutra and Valsalva Maneuver

Anticoagulants are the treatment of choice for pulmonary embolism. When these fail or are contraindicated, vena cava filters are effective devices for preventing clots from the legs from migrating to the lung. Many uncertainties exist when a filter is inserted, especially during physiological activity such as normal breathing and the Valsalva maneuver. These activities are often connected with filter migration and vena cava damage due to the various related vein geometrical configurations. In this work, we analyzed the response of the vena cava during normal breathing and Valsalva maneuver, for a healthy vena cava and after insertion of a commercial Günther-Tulip® filter. Validated computational fluid dynamics (CFD) and patient specific data are used for analyzing blood flow inside the vena cava during these maneuvers. While during normal breathing, the vena cava flow can be considered almost stationary with a very low pressure gradient, during Valsalva the extravascular pressure compresses the vena cava resulting in a drastic reduction of the vein section, a global flow decrease through the cava but increasing the velocity magnitude. This change in the section is altered by the presence of the filter which forces the section of the vena cava before the renal veins to keep open. The effect of the presence of the filter is investigated during these maneuvers showing changes in wall shear stress and velocity patterns.

Computational imaging analysis of glycated fibrin gels reveals aggregated and anisotropic structures

In this article, a computational imaging analysis method is presented for the evaluation of aggregation and anisotropy in both native (unglycated) and glycated fibrin matrix structures. The imaging analysis was used to test the hypothesis that glycated fibrin structures are more aggregated and anisotropic than unglycated (native) fibrin structures. Glycation of fibrinogen, and subsequently fibrin, occurs under normal physiological conditions; however, excess glycation due to disease states such as diabetes can disrupt the fibrin matrix and cause an abnormal structure and function. Studies that elucidate morphological changes in glucose incubated fibrin matrices are necessary to better understand thrombosis, which occurs due to hypercoagulable conditions. In this study, imaging algorithms were designed for the determination of aggregation of fibrin fibers within a matrix as well as preferential orientation (anisotropy) due to glycation. The results showed that glycated fibrin structures displayed an overall higher degree of aggregation and anisotropy as compared to unglycated fibrin structures. However, for glycated fibrin matrices that were polymerized utilizing extended incubation periods representative of physiological plasma glucose conditions, the results showed that fibrin aggregation and anisotropy decreased when compared to unglycated matrices. The algorithms showed that incorporation of the crosslinking agent FXIII into the fibrin matrix was shown to decrease both aggregation and anisotropy. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2191-2198, 2017.

A Computational Method for Predicting Inferior Vena Cava Filter Performance on a Patient-Specific Basis

A computational methodology for simulating virtual inferior vena cava (IVC) filter placement and IVC hemodynamics was developed and demonstrated in two patient-specific IVC geometries: a left-sided IVC and an IVC with a retroaortic left renal vein. An inverse analysis was performed to obtain the approximate in vivo stress state for each patient vein using nonlinear finite element analysis (FEA). Contact modeling was then used to simulate IVC filter placement. Contact area, contact normal force, and maximum vein displacements were higher in the retroaortic IVC than in the left-sided IVC (144 mm2, 0.47 N, and 1.49 mm versus 68 mm2, 0.22 N, and 1.01 mm, respectively). Hemodynamics were simulated using computational fluid dynamics (CFD), with four cases for each patient-specific vein: (1) IVC only, (2) IVC with a placed filter, (3) IVC with a placed filter and model embolus, all at resting flow conditions, and (4) IVC with a placed filter and model embolus at exercise flow conditions. Significant hemodynamic differences were observed between the two patient IVCs, with the development of a right-sided jet, larger flow recirculation regions, and lower maximum flow velocities in the left-sided IVC. These results support further investigation of IVC filter placement and hemodynamics on a patient-specific basis.