Computational Flow Dynamics Analysis Research Articles

Exploring the hemodynamic behavior of residual aneurysms after coiling and clipping: A computational flow dynamic analysis.

Residual intracranial aneurysms post-clipping or coiling pose a poorly established risk of rupture. Computational fluid dynamic (CFD) offers insights into hemodynamic changes following such interventions. This study aims to assess hemodynamic parameters in residual aneurysms pre- and post-treatment with surgical clips or coils using CFD. A retrospective analysis of consecutive patients between January 2015 and January 2024 was conducted. Digital subtraction angiography images were reconstructed using 3D modeling techniques, and hemodynamic parameters were analyzed with ANSYS® software. Six aneurysms were analyzed: Five unruptured and one ruptured. The aneurysms were located at the basilar apex (2), middle cerebral artery bifurcation (2), and origin of the posterior communicating artery (2). Post-treatment, there was a significant reduction in both aneurysm area (median reduction of 33.73%) and volume (median reduction of 25.3%). Five of the six cases demonstrated fewer low wall shear stress (WSS) areas, which could indicate a reduction in regions prone to thrombus formation and diminished risk of rupture. In the unruptured aneurysms, there was a median increase of 137.6% in average WSS. Notably, the only case with increased low WSS area also had the highest increase in average WSS. One basilar artery aneurysm showed increased WSS across all parameters, suggesting a higher rupture risk. The increase in average and high WSS area, along with a decrease in low WSS area, reflects a complex balance between factors of stability and rupture risk. However, a simultaneous increase in all WSS parameters may represent the highest rupture risk due to increased mechanical stress on the aneurysm wall, necessitating closer monitoring.

Computational Flow Dynamic Analysis in Left Atrial Appendage Thrombus Formation Risk: A Review

Atrial fibrillation (AF) is a common cardiac arrhythmia characterized by irregular and rapid electrical activity in the atria, leading to ineffective contraction and poor blood flow. More than 90% of the left atrial (LA) thrombi that cause thromboembolic events during atrial fibrillation (AF) develop in the left atrial appendage (LAA). AF modifies the hemodynamics of the left atrium, which can result in thrombosis of the LAA, systemic embolism, and stroke. The current options to reduce thromboembolic events are oral anticoagulation, surgical LAA exclusion, or percutaneous LAA occlusion. However, the mechanism underlying thrombus development in the LAA remains poorly understood. Computational fluid dynamics (CFD) analysis can be used to better understand the risk of thrombus formation and subsequent embolic events. CFD enables the simulation and visualization of blood flow patterns within the heart, including complex structures such as the LAA. Using CFD, researchers can analyze the hemodynamics of blood flow, identify areas of stagnation or turbulence, and predict the risk of thrombus formation. The correlation between blood flow dynamics, atrial fibrillation, and the risk of stroke has been highlighted by CFD studies investigating the underlying mechanism of thrombus formation in the LAA. This review study intends to provide a comprehensive overview of the factors involved in thrombus formation and their implications for clinical practice by synthesizing the insights acquired from these CFD studies.

Three-dimensional computational flow dynamics analysis of free-surface flow in a converging channel

Three-dimensional computational flow dynamics analysis of free-surface flow in a converging channel

A novel low shear horizontal bioreactor design for the production of animal cells: Effect of bioreactor dynamics on the 3D spheroid formation of HepG2

Studies were carried out on a novel bioreactor designed for the production of animal cells. The aim is, to provide 3D cell proliferation under the influence of low gravity together with gentle mixing and low shear stress. HepG2 cells were used in the experiments to show that this bioreactor can provide low shear forces and a micro-gravity effect considering the results from its Computational Flow Dynamics (CFD) analyses. This bioreactor design has a horizontally positioned cylindrical body and two U-shaped agitators placed opposite to each other. This opposing blade formation, has a reducing effect on each other's hydrodynamic forces and forms a region with low shear stress character in the center of the bioreactor. First of all, the hydrodynamic forces formed inside this bioreactor, which was designed on the basis of CFD simulations, were examined. Afterwards, this novel designed low shear horizontal bioreactor (LSB-R) was manufactured according to the CFD analysis, and simulations. Then, production trials were conducted to determine the success of LSB-R in spheroid production. Thus, by evaluating results obtained from the production trials in accordance with cell culture, it has been shown that LSB-R, which design and patenting phase has been completed, can provide low shear stress.

Abstract 13000: The Effect of Flow Dynamics on the Neotissue Formation of 3D Printed Tissue Engineered Vascular Graft

Introduction: Complex vascular reconstruction such as that of the right ventricle to pulmonary artery (RVPA) and the aortic arch remains challenging due to the various 3D geometry of each patient. Tissue-engineered vascular grafts (TEVG) possess not only excellent antithrombotic and anti-infective properties but also the ability to grow as the patient matures. 3D printed patient-specific TEVG can maintain optimal hemodynamics with the growth of the patient and may improve surgical outcomes. We applied our unique 3D printing technology to create patient-specific TEVG for RVPA and the aortic arch. Methods: We acquired MRI and 4-dimensional flow data for the native anatomy of pigs (n=8) to design a patient-specific TEVG of the pulmonary artery (n=5) and the aortic arch (n=3) 4 weeks prior to surgery. The optimal shape of the branched vascular graft (n=8) was designed using a computer-aided design informed by computational flow dynamics analysis. We manufactured and implanted the grafts into the RVPA or aortic arch in the porcine model. The grafts were explanted after surgery at 8 - 12 weeks for evaluation. Pre- and post-op implant flow dynamics data in MRI and histology were analyzed. Results: The local neointimal thickness of TEVG in histology and the corresponding area of wall shear stress in 4D MRI were measured. Low wall shear stress, an aspect of MRI flow analysis, demonstrated a significant correlation with decreased neointimal thickness through histology (R2=0.65, P=0.016), which suggested optimal shape and design is important for appropriate neotissue formation. Conclusions: Our 3D printed custom designed TEVG demonstrated optimal anatomical fit maintaining ideal flow dynamics can attenuate neointimal hyperplasia and appropriate neovessel formation.

Influence of nozzle clearance of VG turbocharger turbine on performance and internal flow

Abstract To realize a sustainable society, it is necessary to reduce exhaust gas from automobiles and improve fuel efficiency. Turbochargers are useful for the purpose and especially variable geometry (VG) turbochargers are often installed because their nozzle blade angle can be optimally changed according to the rotational speed of the engine. To change the angle, it is needed to provide the nozzle clearance on both hub and shroud sides. In this study, CFD (Computational Flow Dynamics) calculations of a turbocharger turbine were conducted. The rotational speed of the turbine was set to 10,000 rpm. The diameter of the wheel blade is 60 mm and the height of the nozzle blade was 9.71 mm. The following were mainly investigated: the effect of the nozzle clearance position or blade angle on turbine performance, and the effect of leakage vortex from nozzle clearance on the downstream flow in the wheel domain. First, the steady-state CFD analysis on the nozzle and wheel domain was conducted. Four models of nozzle clearance were used: No Clearance (NC), Hub Clearance (HC), Shroud Clearance (SC), and Hub and Shroud Clearance (HSC). And four nozzle blade angles were used. With the Shroud Clearance model, the torque efficiency was worst with every nozzle blade angle. It was also found that the leakage flow rate from the nozzle clearance affects the loss increase in the wheel domain. Second, the unsteady-state CFD analysis on the full domain (casing + nozzle + wheel +diffuser) was conducted to investigate the leakage flow from nozzle clearance. The turbulence model was DES (Detached Eddy Simulation). Hub Clearance model and Shroud clearance model were used. The leakage vortex generated from nozzle clearance was found to flow into the wheel domain. With each nozzle model, the rotating directions of those vortexes were opposite. By the rothalpy loss investigation with the Hub Clearance model, it was confirmed that the portions of wheel domain where two leakage vortexes flow into showed larger losses than other portions. Those portions were located diagonally in two places, and they rotated in the opposite direction to the wheel rotation. On the other hand, with the Shroud Clearance model, the portions where the rothalpy loss was large were not shown regularly.

Abstract P531: Cerebral Blood Flow Analysis Using Flow Wire Measurements and CFD Analysis

Introduction: Clinical reports show that cerebral blood flow conditions are indicative of cerebral vascular disease. While methods for characterizing cerebral vascular flow have been extensively reported in the past, comparative analyses between direct flow measurements (DM) and computational flow dynamic (CFD) analysis remain limited. We hypothesize that flow data can be reliably measured both directly and through CFD in normal vessels. Methods: A left heart replicator was used as a realistic cardiac pump which maintained systolic pressure at 120 mmHg and diastolic pressure at 80 mmHg. A stenotic model with 50% stenosis for the ICA was connected to the replicator. A ComboWire was used for DM and recorded flow pressure and velocity. CFD was used to study flow. Results: In areas at the proximal end of the stenosis, the pressure and flow velocity derived from DM and CFD were in good agreement. At the end of systole and diastole, DM pressure were 145.42 mmHg and 73.53 mmHg, respectively. CFD simulation for the same system obtained the pressure at the end of systole and diastole of 147.16 mmHg and 74.64 mmHg, respectively. The velocity data collected from DM was at 15.40 cm/s and 7.74 cm/s for systolic flow and mean flow velocity. CFD measured flow was 17.85 cm/s and 11.37 cm/s, respectively. In areas at the distal end of the stenosis, pressure data showed good agreement between DM and CFD analysis. The DM were 138 and 70.81 mmHg at the end of systole and diastole, respectively; CFD simulation yielded 145.95 and 74.51 mmHg, respectively. Variations in the velocity data were observed at this location (Fig, pink arrows). Conclusion: DM of pressure showed good agreement with CFD simulation in all areas of the vessel. DM of velocity using the flow wire were highly affected by location of the measurement. CFD analysis can provide more consistent flow data for flow information collection along the vasculature.

Rheological study of fluid flow model through computational flow dynamics analysis and its implications in mud hydraulics

Oil and Gas drilling is not a simple fundamental procedure, never the less it accounts many subsurface uncertainties to deal with. The primary objective of an efficient and optimized drilling program is to analyze the formation uncertainties and chose a systematic logical approach for pursue drilling operations to overcome any problem encountered. Wellbore stability is the most important and cardinal part of drilling i.e. 1. Maintaining wellbore stability limits the Non Productive Time (NPT) for a well and 2. Analyzing the GTO to select a logical and effective approach for drilling saves time and allows remedial measures to get prepared for instability if encountered. During the process of drilling, the stability of wellbore is achieved by minimizing the fractures across the wellbore, which will occur mainly due to imbalanced mechanical forces. If the stresses acting on the wellbore surfaces increases then there will be a chance of pipe stuck due to formation collapse, which makes the wellbore cleaning difficult. The present paper deals in accordance with developing an understanding of the problems associated with wellbore instabilities and focuses on designing of proper drilling fluids formulations to counter these problems. The major experiments conducted are for analysis of formulating mud, namely: a. KCL-Polymer mud system b. Salt saturated mud system. Designing of drilling fluid done for Water Based Mud Systems only using additives in different proportions to maximize control and ensure cost effectiveness of the mud. Apart from the above oil well cleaning has been approached by the Navier stoke’s equation, power model, continuity equation to develop a mathematical model to help us understand the lifting of the cuttings as a function of fluid viscosity, density, fluid velocity. This in turn helps us to generate the flow regimes near the wellbore around the tubing while transporting the cuttings. The phase of CFD analyses has initiated with the motto of understanding the flow models and verifying the graphs generated from the simulation on the conventional Software’s.

Abstract WMP36: Wall Shear Stress Disturbances May Be Key Requirements for Cerebral Aneurysm Growth: Computational Flow Dynamic Analysis of 15 Cases in NHO CFD ABO Study

Introduction: In 2013, we conducted a multi-institutional prospective observational study in order to identify hemodynamic environments involved in the rupture and growth of unruptured cerebral aneurysms by computational fluid dynamic (CFD) analysis (National Hospital Organization CFD ABO Study: UMIN000013584). There were 461 cases registered and observed for 3 years on the condition that 3DCTA and carotid echocardiography were performed every year. The observation period ended at the end of March this year. There were 32 cases that enlarged, and 209 cases that did not enlarge or rupture after 3 years of observation period. Here, 15 growing cases and 15 non-growing cases were hemodynamically evaluated. Methods: Pulsatile blood flow was simulated using ANSYS-CFX, based on the Navier-Stokes equations for incompressible fluid. Multivariate regression analysis was performed to find differences between growing and non-growing aneurysms in wall shear stress (WSS) magnitude-based metrics (WSS, WSSG, NWSS, NWSSG) and WSS disturbance-based metrics (OSI as a metric for unidirectional WSS disturbance, NtransWSS as a metric for multi-directional WSS disturbance)on the CFD modelling after adjustment for age, sex, hypertension, smoking history, and aneurysm size and location. Results and Conclusions: In the growing and non-growing aneurysms, the average age was 71.8 ± 12.6 and 66.3 ± 11.1 years, the maximum diameter 5.48 ± 2.64 and 5.47 ± 1.85 mm, female 10 and 6 cases, HT 10 and 10, smoking 6 and 11, respectively. Both OSI (p=0.0215) and NtransWSS (p=0.0428) were significantly higher in growing aneurysms compared to non-growing ones, whereas there were no significant differences in WSS magnitude-based metrics(figure). The data suggested that WSS disturbances may be closely associated with the growth of cerebral aneurysms.

In vivo implantation of 3-dimensional printed customized branched tissue engineered vascular graft in a porcine model

BackgroundThe customized vascular graft offers the potential to simplify the surgical procedure, optimize physiological function, and reduce morbidity and mortality. This experiment evaluated the feasibility of a flow dynamic–optimized branched tissue engineered vascular graft (TEVG) customized based on medical imaging and manufactured by 3-dimensional (3D) printing for a porcine model. MethodsWe acquired magnetic resonance angiography and 4-dimensional flow data for the native anatomy of the pigs (n = 2) to design a custom-made branched vascular graft of the pulmonary bifurcation. An optimal shape of the branched vascular graft was designed using a computer-aided design system informed by computational flow dynamics analysis. We manufactured and implanted the graft for pulmonary artery (PA) reconstruction in the porcine model. The graft was explanted at 4 weeks after implantation for further evaluation. ResultsThe custom-made branched PA graft had a wall shear stress and pressure drop (PD) from the main PA to the branch PA comparable to the native vessel. At the end point, magnetic resonance imaging revealed comparable left/right pulmonary blood flow balance. PD from main PA to branch between before and after the graft implantation was unchanged. Immunohistochemistry showed evidence of endothelization and smooth muscle layer formation without calcification of the graft. ConclusionsOur animal model demonstrates the feasibility of designing and implanting image-guided, 3D-printed, customized grafts. These grafts can be designed to optimize both anatomic fit and hemodynamic properties. This study demonstrates the tremendous potential structural and physiological advantages of customized TEVGs in cardiac surgery.

Haemodynamic stress-induced breaches of the arterial intima trigger inflammation and drive atherogenesis.

Inflammatory mediators, including blood cells and their products, contribute critically to atherogenesis, but the igniting triggers of inflammation remain elusive. Atherosclerosis develops at sites of flow perturbation, where the enhanced haemodynamic stress could initiate the atherogenic inflammatory process due to the occurrence of mechanic injury. We investigated the role of haemodynamic stress-induced breaches, allowing the entry of blood cells in the arterial intima, in triggering inflammation-driven atherogenesis. Human coronary samples isolated from explanted hearts, (n = 47) displayed signs of blood entry (detected by the presence of iron, ferritin, and glycophorin A) in the subintimal space (54%) as assessed by histology, immunofluorescence, high resolution episcopic microscopy, and scanning electron microscopy. Computational flow dynamic analysis showed that intimal haemorrhagic events occurred at sites of flow disturbance. Experimental carotid arteries from Apoe deficient mice showed discrete endothelial breaches and intimal haemorrhagic events specifically occurring at the site of flow perturbation, within 3 days after the exacerbation of the local haemodynamic stress. Endothelial tearing was associated with increased VCAM-1 expression and, within 7 days, substantial Ly6G+ leucocytes accumulated at the sites of erythrocyte-derived iron and lipids droplets accumulation, pathological intimal thickening and positive oil red O staining. The formation of fatty streaks at the sites of intimal breaches was prevented by the depletion of Ly6G+ leucocytes, suggesting that the local injury driven by haemodynamic stress-induced breaches triggers atherogenic inflammation. Haemodynamic-driven breaches of the arterial intima drive atherogenic inflammation by triggering the recruitment of leucocyte at sites of disturbed arterial flow.

Rheolytic effects of left main mid-shaft/distal stenting: a computational flow dynamic analysis.

Background The aim of this study was to evaluate the rheolytic effects of stenting a mid-shaft/distal left main coronary artery (LMCA) lesion with and without ostial coverage. Stenting of the LMCA has emerged as a valid alternative in place of traditional coronary bypass graft surgery. However, in case of mid-shaft/distal lesion, there is no consensus regarding the extension of the strut coverage up to the ostium or to stent only the culprit lesion. Methods We reconstructed a left main-left descending coronary artery (LM-LCA)-left circumflex (LCX) bifurcation after analysing 100 consecutive patients (mean age 71.4 ± 9.3, 49 males) with LM mid-shaft/distal disease. The mean diameter of proximal LM, left anterior descending (LAD) and LCX, evaluated with quantitative coronary angiography (QCA) was 4.62 ± 0.86 mm, 3.31 ± 0.92 mm, and 2.74 ± 0.93 mm, respectively. For the stent simulation, a third-generation, everolimus-eluting stent was virtually reconstructed. Results After virtual stenting, the net area averaged wall shear stress (WSS) of the model and the WSS at the LCA-LCX bifurcation resulted higher when the stent covered the culprit mid-shaft lesion only compared with the extension of the stent covering the ostium (3.68 versus 2.06 Pa, p = 0.01 and 3.97 versus 1.98 Pa, p < 0.001, respectively. Similarly, the static pressure and the Reynolds number were significantly higher after stent implantation covering up the ostium. At the ostium, the flow resulted more laminar when stenting only the mid-shaft lesion than including the ostium. Conclusions Although these findings cannot be translated directly into real practice our brief study suggests that stenting lesion 1:1 or extending the stent to cover the LM ostium impacts differently the rheolytic properties of LMCA bifurcation with potential insights for restenosis or thrombosis.

Computational Flow Dynamic Analysis of Right and Left Atria in Patent Foramen Ovale: Potential Links with Atrial Fibrillation.

An impairment of the left atrial function similar to that usually observed in atrial fibrillation (AF) has been observed also in patients with patent foramen ovale (PFO) and permanent right-to-left shunting (RLS). We reconstructed the geometrical model of right atrium (RA), PFO, left atrium (LA) and left atrial appendage (LAA) of 65 patients with mild (36 patients mean age 45.5±6.8 years, 24 females) or permanent (29 patients, mean age 45.1±5.3 years, 21 females) RLS using anatomical data obtained by transoesophageal echocardiography (TEE) and cardiac MRI, performed as a part of our institutional screening protocol for paradoxical embolism. Using computational fluid dynamic analysis (CFD) we assessed the vorticity magnitude in both the LA and LAA to analyse a possible rheological relationship between PFO and AF. The anatomical models, in terms of dimensions, were comparable among the patients with mild and permanent RLS. A higher vorticity magnitude was observed in the mild shunt both in the LA (101.12±21.3 vs 88.3±22.6, p=0.02) and LAA (62±14.4 vs 32.4±12.3, p<0.01) when compared to the permanent R-L shunting. The lower vorticity magnitude across the LA and LAA in patients with permanent RLS suggests a possible higher stagnation of the blood in these anatomical sites, similarly as previously observed in patients with AF.

Longer coronary anastomosis provides lower energy loss in coronary artery bypass grafting.

Distal anastomosis technique affects graft patency and long-term outcomes in coronary artery bypass grafting, however, there is no standard for the appropriate length of distal anastomosis. The purpose of this study is to evaluate whether longer distal anastomosis provides higher quality of distal anastomosis and better hemodynamic patterns. Off pump CABG training simulator, YOUCAN (EBM Corporation, Japan), was used for distal anastomosis model. Two lengths of distal anastomosis model (10 versus 4mm) were prepared by end-to-side anastomosis technique. After CT scan constructed three-dimensional inner shape of distal anastomosis, computational flow dynamics (CFD) was used to analyze hemodynamic patterns. The working flow was defined as Newtonian fluid with density of 1050kg/m3 and viscosity of 4mPas. The boundary condition was set to 100mmHg at inlet, 50ml/min at outlet, and 100% stenosis of proximal coronary artery. Three-dimensional CT imaging showed quality of distal anastomosis in 10mm model was more uniform without vessel wall inversion or kinking compared to 4mm model. Anastomotic flow area was significantly larger in 10mm model than that in 4mm model (28.67±4.91 versus 8.89±3.18mm2, p<0.0001). Anastomotic angle was significantly smaller in 10mm model compared to 4mm model (10.2±5.65° versus 20.6±3.31°, p<0.0001). CFD analysis demonstrated 10mm model had streamlined flow with smooth graft curvature, whereas 4mm model had abrupt blood flow direction changes with flow separation at the toe. 10mm model had significantly lower energy loss than 4mm model (34.78±6.90 versus 77.10±21.47μW, p<0.0001). Longer distal anastomosis provided higher quality of distal anastomosis, larger anastomotic flow area, smaller anastomotic angle, and smoother graft curvatures. These factors yielded lower energy loss at distal anastomosis.

Computational Flow Dynamics of the Severe M1 Stenosis Before and After Stenting

PurposeComputational flow dynamic (CFD) study has not been widely applied in intracranial artery stenosis due to requirement of high resolution in identifying the small intracranial artery. We described a process in CFD study applied to symptomatic severe intracranial (M1) stenosis before and after stenting.Materials and MethodsReconstructed 3D angiography in STL format was transferred to Magics (Materialise NV, Leuven, Belgium) for smoothing of vessel surface and trimming of branch vessels and to HyperMesh (Altair Engineering Inc., Auckland, New Zealand) for generating tetra volume mesh from triangular surface-meshed 3D angiogram. Computational analysis of blood flow in the blood vessels was performed using the commercial finite element software ADINA Ver 8.5 (ADINA R & D, Inc., Lebanon, MA). The distribution of wall shear stress (WSS), peak velocity and pressure in a patient was analyzed before and after intracranial stenting.ResultsComputer simulation of wall shear stress, flow velocity and wall pressure before and after stenting could be demonstrated three dimensionally by video mode according to flow vs. time dimension. Such flow model was well correlated with angiographic finding related to maximum degree of stenosis. Change of WSS, peak velocity and pressure at the severe stenosis was demonstrated before and after stenting. There was no WSS after stenting in case without residual stenosis.ConclusionOur study revealed that CFD analysis before and after intracranial stenting was feasible despite of limited vessel wall dimension and could reveal change of WSS as well as flow velocity and wall pressure.

A proposed parent vessel geometry—based categorization of saccular intracranial aneurysms: computational flow dynamics analysis of the risk factors for lesion rupture

The authors created a simple, broadly applicable classification of saccular intracranial aneurysms into three categories: sidewall (SW), sidewall with branching vessel (SWBV), and endwall (EW) according to the angiographically documented patterns of their parent arteries. Using computational flow dynamics analysis (CFDA) of simple models representing the three aneurysm categories, the authors analyzed geometry-related risk factors such as neck width, parent artery curvature, and angulation of the branching vessels. The authors performed CFDAs of 68 aneurysmal geometric formations documented on angiograms that had been obtained in patients with 45 ruptured and 23 unruptured lesions. In successfully studied CFDA cases, the wall shear stress, blood velocity, and pressure maps were examined and correlated with aneurysm rupture points. Statistical analysis of the cases involving aneurysm rupture revealed a statistically significant correlation between aneurysm depth and both neck size (p < 0.0001) and caliber of draining arteries (p < 0.0001). Wider-necked aneurysms or those with wider-caliber draining vessels were found to be high-flow lesions that tended to rupture at larger sizes. Smaller-necked aneurysms or those with smaller-caliber draining vessels were found to be low-flow lesions that tended to rupture at smaller sizes. The incidence of ruptured aneurysms with an aspect ratio (depth/neck) exceeding 1.6 was 100% in the SW and SWBV categories, whereas the incidence was only 28.75% for the EW aneurysms. The application of standardized categories enables the comparison of results for various aneurysms' geometric formations, thus assisting in their management. The proposed classification system may provide a promising means of understanding the natural history of saccular intracranial aneurysms.