Flow Wall Shear Stress Research Articles

A mathematical model that describes the relation of low-density lipoprotein and oxygen concentrations in a stenosed artery

The cellular activities of the endothelium layer between lumen and intima are significantly linked to the origin of the disease atherosclerosis. Three stages of atherosclerosis were investigated in this study (40%-mild, 50%-modest, and 60%-acute) concerning the coronary arterial segment. The essence of the hemodynamic factors like flow velocity, pressure, and wall shear stress has been investigated, as well as the interrelationships between them. At all degrees of stenosis, the biophysical relationship between convection-diffusion of low-density lipoproteins (LDL) and convection-diffusion of oxygen in the bloodstream is investigated. The Finite Element Methods (FEM) are used to solve the modeled partial differential equation systems. The method adopted is numerical in nature providing accurate graphical solutions to the framed systems. The physical effects of the deposition of LDL on the arterial wall, like a decrease in the diameter of the lumen, and toughening of the walls, are analyzed through the evaluation of the physical parameters. The study revealed that the deposition of LDL molecules in the post stenotic region leads to the depletion of oxygen in the region leading to the rapid dysfunctioning of the endothelial layer of the lumen-intima boundary.

Integrating particle tracking with computational fluid dynamics to assess haemodynamic perturbation by coronary artery stents.

AimsCoronary artery stents have profound effects on arterial function by altering fluid flow mass transport and wall shear stress. We developed a new integrated methodology to analyse the effects of stents on mass transport and shear stress to inform the design of haemodynamically-favourable stents.Methods and resultsStents were deployed in model vessels followed by tracking of fluorescent particles under flow. Parallel analyses involved high-resolution micro-computed tomography scanning followed by computational fluid dynamics simulations to assess wall shear stress distribution. Several stent designs were analysed to assess whether the workflow was robust for diverse strut geometries. Stents had striking effects on fluid flow streamlines, flow separation or funnelling, and the accumulation of particles at areas of complex geometry that were tightly coupled to stent shape. CFD analysis revealed that stents had a major influence on wall shear stress magnitude, direction and distribution and this was highly sensitive to geometry.ConclusionsIntegration of particle tracking with CFD allows assessment of fluid flow and shear stress in stented arteries in unprecedented detail. Deleterious flow perturbations, such as accumulation of particles at struts and non-physiological shear stress, were highly sensitive to individual stent geometry. Novel designs for stents should be tested for mass transport and shear stress which are important effectors of vascular health and repair.

Role of patient-specific blood properties in computational fluid dynamics simulation of flow diverter deployed cerebral aneurysms.

BACKGROUND: Hemodynamics and their clinical outcome of cerebral aneurysms treated with flow diverter (FD) stents have thus far been investigated using computational fluid dynamics (CFD) simulations. Although human blood is characterized as a non-Newtonian patientspecific fluid, non-patient-specific blood properties (PSBP) were applied in most extant studies.OBJECTIVE: To investigate the hemodynamic effects caused by PSBPs in aneurysms treated with FD stents.METHODS: We measured blood properties (density and viscosity) for 12 patients who underwent FD stent deployment. We conducted CFD simulations with the measured PSBPs and non-PSBPs quoted from previous studies. The average blood flow velocity and wall shear stress within the aneurysms were calculated and two simulation patterns were compared.RESULTS: The velocity and wall shear stress changed by 2.93% and 3.16% on average, respectively, without an FD stent deployed. Conversely, with the FD stents deployed, the change rates increased to 11.1% and 9.06% on average, respectively.CONCLUSIONS: The change in hemodynamic parameters if PSBPs are considered, may not be negligible when conducting CFD simulations of FD stent deployed aneurysms To obtain an adequate hemodynamic environment for cerebral aneurysms with FD stents deployed, it is recommended to use PSBPs for CFD simulations.

Hemodynamic Comparison of Treatment Strategies for Intracranial Vertebral Artery Fusiform Aneurysms.

ObjectiveThis study comparatively analyzed the hemodynamic changes resulting from various simulated stent-assisted embolization treatments to explore an optimal treatment strategy for intracranial vertebral artery fusiform aneurysms. An actual vertebral fusiform aneurysm case treated by large coil post-stenting (PLCS) was used as a control.Materials and MethodsA single case of an intracranial vertebral artery fusiform aneurysm underwent a preoperative and eight postoperative finite element treatment simulations: PLCS [single and dual Low-profile Visualized Intraluminal Support (LVIS)], Jailing technique (single and dual LVIS both simulated twice, Pipeline Embolization Device (PED) with or without large coils (LCs). Qualitative and quantitative assessments were performed to analyze the most common hemodynamic risk factors for recurrence.ResultsJailing technique and PED-only had a high residual flow volume (RFV) and wall shear stress (WSS) on the large curvature of the blood flow impingement region. Quantitative analysis determined that PLSC and PED had a lower RFV compared to preoperative than did the jailing technique [PED+LC 2.46% < PLCS 1.2 (dual LVIS) 4.75% < PLCS 1.1 (single LVIS) 6.34% < PED 6.58% < Jailing 2.2 12.45% < Jailing 1.2 12.71% < Jailing 1.1 14.28% < Jailing 2.1 16.44%]. The sac-averaged flow velocity treated by PLCS, PED and PED+LC compared to preoperatively was significantly lower than the jailing technique [PED+LC = PLCS 1.2 (dual LVIS) 17.5% < PLCS 1.1 (single LVIS) = PED 27.5% < Jailing 1.2 = Jailing 2.2 32.5% < Jailing 1.1 37.5% < Jailing 2.1 40%]. The sac-averaged WSS for the PLCS 1.2 (dual LVIS) model was lower than the PED+LC, while the high WSS area of the Jailing 1 model was larger than for Jailing 2 [PLCS 1.2 38.94% (dual LVIS) < PED+LC 41% < PLCS 1.1 43.36% (single LVIS) < PED 45.23% < Jailing 2.1 47.49% < Jailing 2.2 47.79% < Jailing 1.1 48.97% < Jailing 1.2 49.85%].ConclusionsFor fusiform aneurysms, post large coil stenting can provide a uniform coil configuration potentially reducing the hemodynamic risk factors of recurrence. Flow diverters also may reduce the recurrence risk, with long-term follow-up required, especially to monitor branch blood flow to prevent postoperative ischemia.

Inflow Angle Impacts Morphology, Hemodynamics, and Inflammation of Side-wall Intracranial Aneurysms.

Aneurysm inflow angle has been shown to be associated with hemodynamic changes by computational fluid dynamics. However, these studies were based on single aneurysm model and were limited to side-wall aneurysms. To investigate the association between inflow angle and morphology, hemodynamic, and inflammation of intracranial side-wall and bifurcation aneurysms. Prospective. A total of 62 patients (aged 58.34 ± 12.39, 44 female) with 59 unruptured side-wall aneurysms and 17 unruptured bifurcation aneurysms were included. A 3.0 T; 3D fast field echo sequence (TOF-MRA); free-breathing, 3D radio-frequency-spoiled, multi-shot turbo field echo sequence (4D-flow MRI); 3D black-blood T1-weighted volumetric turbo spin echo acquisition sequence (T1 -VISTA) ASSESSMENT: Two neuroradiologists assessed the inflow angle and size for intracranial aneurysms in 3D space with TOF-MRA images. The average and maximum inflow velocity (Vavg-IA , Vmax-IA ), blood flow (Flowavg-IA , Flowmax-IA ), and average wall shear stress (WSSavg-IA ) for aneurysms were assessed from 4D-flow MRI in regions of interest drawn by two neuroradiologists. The aneurysmal wall enhancement (AWE) grades between precontrast and postcontrast T1 -VISTA images were evaluated by three neuroradiologists. Kruskal-Wallis H test, χ2 test, Pearson's correlation coefficient, scatter plots and regression lines, multivariate logistic regression analysis (partial correlation r) were performed. A P < 0.05 was considered statistically significant. The WSSavg-IA (0.52 ± 0.34 vs. 0.27 ± 0.22) and AWE grades (1.38 ± 1.04 vs. 2.02 ± 0.68) between the two inflow angle subgroups of side-wall aneurysms were significantly different. The aneurysm size (rs =0.31), WSSavg-IA (rs =-0.45), and AWE grades (rs =0.45) were significantly correlated with inflow angle in side-wall aneurysms. While in bifurcation aneurysms, there were no significant associations between inflow angle and size (P=0.901), Vavg-IA (P=0.699), Vmax-IA (P=0.482), Flowavg-IA (P=0.550), Flowmax-IA (P=0.689), WSSavg-IA (P=0.573), and AWE grades (P=0.872). A larger aneurysm size, a lower WSS and a higher AWE grade were correlated with a larger inflow angle in side-wall aneurysms. 3 TECHNICAL EFFICACY: Stage 2.

Can vessel sea chest design improve fouling control coating performance?

Sea chests are arguably the most problematic vessel niche areas with respect to managing and preventing marine biofouling. This is partly due to the design and location of these structures, as well as the difficulty in managing them with conventional antifouling technologies. Antifouling coatings are typically designed for use on flat exposed hull surfaces that experience predictable flow conditions, and often perform poorly under variable flow conditions found in sea chest environments. This study examined whether custom-designed inserts retrofitted to experimental sea chests to alter their internal geometry and flow characteristics could improve antifouling coating performance. For in-laboratory sea chests coated with self-polishing copolymer (SPC) antifouling coatings, retrofitted inserts improved the polishing rate and erosion consistency of the coating; likely due to enhanced laminar flow and greater uniform wall shear stress over the surface of the sea chest, and the elimination of circulation zones and/or pockets of static water. For in-field sea chests coated with fouling-release coatings, inserts had little direct impact on biofouling accumulation compared to unmodified sea chests, with similar levels of fouling recorded per cm2 of sea chest surface. Inserts did however reduce the overall biomass of biofouling accumulated, through a reduction in available settlement area.

Characteristic effect of wall elasticity on flow instability and wall shear stress of a full-scale, patient-specific aneurysm model in the middle cerebral artery: An experimental approach

The mechanisms underlying the growth and rupture of aneurysms are poorly understood. Although the wall shear stress (WSS) in elastic aneurysm models is examined using fluid-structure interaction (FSI) simulations, it has not been sufficiently validated using experimental modalities, such as particle image velocimetry (PIV) or phase contrast magnetic resonance imaging (PC-MRI). In this study, we investigated pulsatile flow in an elastic, image-based, patient-specific cerebral aneurysm model using PIV. The phantom model was carefully fabricated using a specialized technique by silicone elastomer. We explored the hemodynamics of the WSS and the kinetic energy cascade (KEC) in the elastic model compared with a rigid model, at the apex of the bifurcation of the middle cerebral artery (MCA) in vitro. The effects of elasticity on the WSS, WSS gradient (WSSG), and tensile strength of the aneurysm wall were also investigated, in addition to the effect of wall elasticity on the KEC compared to a rigid wall. Although the WSSG around the stagnation point had a large positive value, there was no difference between the two models. In particular, wall elasticity suppressed the WSS magnitude around the stagnation point and attenuated the KEC (i.e., the flow fluctuation). Future studies examining KEC frequency and WSS characteristics in a phantom model should consider assessing elasticity.

Bistability of Dielectrically Anisotropic Nematic Crystals and the Adaptation of Endothelial Collectives to Stress Fields.

Endothelial monolayers physiologically adapt to flow and flow‐induced wall shear stress, attaining ordered configurations in which elongation, orientation, and polarization are coherently organized over many cells. Here, with the flow direction unchanged, a peculiar bi‐stable (along the flow direction or perpendicular to it) cell alignment is observed, emerging as a function of the flow intensity alone, while cell polarization is purely instructed by flow directionality. Driven by the experimental findings, the parallelism between endothelia is delineated under a flow field and the transition of dual‐frequency nematic liquid crystals under an external oscillatory electric field. The resulting physical model reproduces the two stable configurations and the energy landscape of the corresponding system transitions. In addition, it reveals the existence of a disordered, metastable state emerging upon system perturbation. This intermediate state, experimentally demonstrated in endothelial monolayers, is shown to expose the cellular system to a weakening of cell‐to‐cell junctions to the detriment of the monolayer integrity. The flow‐adaptation of monolayers composed of healthy and senescent endothelia is successfully predicted by the model with adjustable nematic parameters. These results may help to understand the maladaptive response of in vivo endothelial tissues to disturbed hemodynamics and the progressive functional decay of senescent endothelia.

Thermal effects of two immiscible fluids through a permeable stenosed artery having nanofluid in the core region

AbstractA theoretical investigation of two‐layered fluid flow in a stenosed tube having permeable walls is studied. The fluid (blood with nanoparticles) within the core region behaves as a non‐Newtonian fluid (nanofluid) and the fluid within the peripheral layer behaves as a Newtonian fluid. Flow equations are linearized considering mild stenoses. The closed form mathematical expressions for flow resistance and wall shear stress are computed. The problem is solved using HPM (homotopy perturbation method). The numerical calculations of flow parameters (like flow resistance, wall shear stress) are performed and are discussed graphically. A novel result is found that with increased permeability and viscosity, the resistance of the fluid flow and shear at the wall is found to decrease. Moreover, the velocity profiles are increasing in the radial direction with the enhancement of viscosity of the fluid in the peripheral layer but decrease with permeability. Streamlines are drawn to examine the flow pattern.

Hemodynamic and Structural Comparison of Human Fetal Heart Development Between Normally Growing and Hypoplastic Left Heart Syndrome-Diagnosed Hearts.

Congenital heart defects (CHDs) affect a wide range of societies with an incidence rate of 1.0–1.2%. These defects initiate at the early developmental stage and result in critical health disorders. Although genetic factors play a role in the formation of CHDs, the occurrence of cases in families with no history of CHDs suggests that mechanobiological forces may also play a role in the initiation and progression of CHDs. Hypoplastic left heart syndrome (HLHS) is a critical CHD, which is responsible for 25–40% of all prenatal cardiac deaths. The comparison of healthy and HLHS hearts helps in understanding the main hemodynamic differences related to HLHS. Echocardiography is the most common imaging modality utilized for fetal cardiac assessment. In this study, we utilized echocardiographic images to compare healthy and HLHS human fetal hearts for determining the differences in terms of heart chamber dimensions, valvular flow rates, and hemodynamics. The cross-sectional areas of chamber dimensions are determined from 2D b-mode ultrasound images. Valvular flow rates are measured via Doppler echocardiography, and hemodynamic quantifications are performed with the use of computational fluid dynamics (CFD) simulations. The obtained results indicate that cross-sectional areas of the left and right sides of the heart are similar for healthy fetuses during gestational development. The left side of HLHS heart is underdeveloped, and as a result, the hemodynamic parameters such as flow velocity, pressure, and wall shear stress (WSS) are significantly altered compared to those of healthy hearts.

Vascular Injury in the Zebrafish Tail Modulates Blood Flow and Peak Wall Shear Stress to Restore Embryonic Circular Network.

Mechano-responsive signaling pathways enable blood vessels within a connected network to structurally adapt to partition of blood flow between organ systems. Wall shear stress (WSS) modulates endothelial cell proliferation and arteriovenous specification. Here, we study vascular regeneration in a zebrafish model by using tail amputation to disrupt the embryonic circulatory loop (ECL) at 3 days post fertilization (dpf). We observed a local increase in blood flow and peak WSS in the Segmental Artery (SeA) immediately adjacent to the amputation site. By manipulating blood flow and WSS via changes in blood viscosity and myocardial contractility, we show that the angiogenic Notch-ephrinb2 cascade is hemodynamically activated in the SeA to guide arteriogenesis and network reconnection. Taken together, ECL amputation induces changes in microvascular topology to partition blood flow and increase WSS-mediated Notch-ephrinb2 pathway, promoting new vascular arterial loop formation and restoring microcirculation.

Contrast Agent-Free Assessment of Blood Flow and Wall Shear Stress in the Rabbit Aorta using Ultrasound Image Velocimetry.

Blood flow velocity and wall shear stress (WSS) influence and are influenced by vascular disease. Their measurement is consequently useful in the laboratory and clinic. Contrast-enhanced ultrasound image velocimetry (UIV) can estimate them accurately but the need to inject contrast agents limits utility. Singular value decomposition and high-frame-rate imaging may render contrast agents dispensable. Here we determined whether contrast agent-free UIV can measure flow and WSS. In simulation, accurate measurements were achieved with a signal-to-noise ratio of 13.5 dB or higher. Signal intensity in the rabbit aorta increased monotonically with mechanical index; it was lowest during stagnant flow and uneven across the vessel. In vivo measurements with contrast-free and contrast-enhanced UIV differed by 4.4% and 1.9% for velocity magnitude and angle and by 9.47% for WSS. Bland–Altman analysis of waveforms revealed good agreement between contrast-free and contrast-enhanced UIV. In five rabbits, the root-mean-square errors were as low as 0.022 m/s (0.81%) and 0.11 Pa (1.7%). This study indicates that with an optimised protocol, UIV can assess flow and WSS without contrast agents. Unlike contrast-enhanced UIV, contrast-free UIV could be routinely employed.

Abstract TMP6: Computational Hemodynamic Analysis Of Intra-Aneurysmal Effects Due To Flow Diverter Stent Deployment Conformation

Introduction: Inflow blockage of aneurysms treated with flow diverter stents is dependent on the deployed braid angle (ϕ)—the angle between the yarns which comprise the stent braids and the longitudinal axis of the braid. We utilized computational fluid dynamic (CFD) analysis to examine the effects of braid angle on intra-aneurysmal hemodynamic parameters associated with long-term treatment success. Methods: Two flow diverter stents measuring 3.5 mm in diameter, each containing 88 strands with ϕ = 10° and ϕ = 35° were constructed and deployed into a patient model of an internal carotid artery saccular aneurysm containing pulsatile blood flow. Intra-aneurysmal flow velocity, pulsatility index (PI), turbulence, vorticity, and wall shear stress (WSS) parameters were obtained and compared for the two braid angles. Results: Reducing ϕ from 35° to 10° resulted in -2.59%, -1.92%, and -1.41% changes in systolic bulk velocity, and -1.79%, +0.57%, and -1.65% changes in PI at the aneurysm neck, body, and dome respectively. Vorticity changes were insignificant. High turbulence extending through the aneurysm neck peaked approximately 0.04 s later in systole, and was located closer to the parent vessel outlet when ϕ = 10°. Elevated intra-aneurysmal WSS was concentrated at the neck and body on the side of the parent vessel outlet for both ϕ = 10° and ϕ = 35°. Regions of WSS in excess of 10 Pa stretched higher into the aneurysm body when ϕ = 35°. Conclusion: Stenting at a lower ϕ resulted in higher blockage of flow and better reduction of WSS for initiating and facilitating long term intra-aneurysmal thrombosis. CFD analysis incorporating precise reconstruction of the stent deployment conformation into patient models can provide detailed visualization of flow parameters for assessing potential treatment efficacy throughout the diagnostic and treatment phases of patient care.

Retrograde flow in aortic isthmus in normal and fetal heart disease by principal component analysis and computational fluid dynamics.

Reverse flow Retrograde flow (RF) of blood in the aortic isthmus can be observed in different types of fetal heart disease (FHD), including abnormalities in heart structure and function. This study sought to investigate the relationship between RF and blood flow parameters, and develop a computational fluid dynamics (CFD) model to understand the mechanisms underlying this observation. A total of 281 fetuses (gestational age [GA] 26.6±.3weeks) with FHD and 2803 normal fetuses (GA: 26.1±.1weeks) by fetal echocardiography collected from May 2016 to December 2018. Principal component analysis (PCA) was performed to find the relationship and the CFD model reconstructed from 3D/4D spatio-temporal image correlation (STIC) images to simulate hemodynamics. There was a significant difference in the percentages of RF between the study (80/201 (39%)) and control (29/2803 (1%)) groups (p<0.05). The RF occur when the aorta flow rate (left heart) is reduced to 60% by CFD stimulation. Pearson correlation analysis showed significant correlations between flow rate and wall shear stress(WSS) (r=.883, p=0.047) variables at the AI. Volumetric flow rate of AO or left heart was the main component of the cause of RF. The hemodynamics of the cardiovascular system have highly complex behavior hinge on the turbulent nature of circulating blood flow.

A comparative study on computational fluid dynamic, fluid-structure interaction and static structural analyses of cerebral aneurysm

ABSTRACT Computational Fluid Dynamics (CFD) and Fluid-Structure Interaction (FSI) are increasingly used to predict the hemodynamic and structural behaviors of cerebral aneurysms (CAs) whilst a less-pursued method is the static structural analysis (SSA) using the finite element method. In this paper, hemodynamic parameters including the flow velocity and wall shear stress predicted by CFD and FSI are compared whilst structural parameters including the wall displacement and wall stress predicted by SSA and FSI are compared for four patient-specific CA models under different systolic/diastolic pressures. The predicted distribution patterns of the same parameters for the same CA model under different pressures are similar. However, the percentage differences of the maximum hemodynamic parameters increase with increasing pressure. Conversely, the percentage differences of the maximum structural parameters decrease from a few to less than 1.5% when the systolic/diastolic pressure changes from 120/80 to 180/110 mmHg. The ratio of the computation times for CFD, SSA and FSI is typically 75:1:165. If the maximum wall stress under either ongoing or temporary hypertension is the most critical factor for immediate rupture and, thus, clinical treatment of CAs, SSA can provide a low cost and efficient predictions close to those of FSI for assessing the rupture risk.

Study of Effect of Boundary Conditions on Patient-Specific Aortic Hemodynamics

Cardiovascular computational fluid dynamics (CFD) based on patient-specific modeling is increasingly used to predict changes in hemodynamic parameters before or after surgery/interventional treatment for aortic dissection (AD). This study investigated the effects of flow boundary conditions (BCs) on patient-specific aortic hemodynamics. We compared the changes in hemodynamic parameters in a type A dissection model and normal aortic model under different BCs: inflow from the auxiliary and truncated structures at aortic valve, pressure control and Windkessel model outflow conditions, and steady and unsteady inflow conditions. The auxiliary entrance remarkably enhanced the physiological authenticity of numerical simulations of flow in the ascending aortic cavity. Thus, the auxiliary entrance can well reproduce the injection flow from the aortic valve. In addition, simulations of the aortic model reconstructed with an auxiliary inflow structure and pressure control and the Windkessel model outflow conditions exhibited highly similar flow patterns and wall shear stress distribution in the ascending aorta under steady and unsteady inflow conditions. Therefore, the inflow structure at the valve plays a crucial role in the hemodynamics of the aorta. Under limited time and calculation cost, the steady-state study with an auxiliary inflow valve can reasonably reflect the blood flow state in the ascending aorta and aortic arch. With reasonable BC settings, cardiovascular CFD based on patient-specific AD models can aid physicians in noninvasive and rapid diagnosis.

Influence of the femoral artery-graft junction patient-specific geometry on blood flow structure and wall shear stress

The paper presents a comparative numerical study of pulsatory blood flow in five patient-specific models of femoral-popliteal artery anastomosis. Three-dimensional geometric models of a proximal junction of the common femoral artery/graft were constructed on the bases of CT angiography. The influence of junction geometry on the blood flow and wall shear stress is analyzed. The ratio of the measured CFA and graft diameters and the junction angle are considered as the major geometrical parameters. Numerically calculated velocity fields are analyzed, and stagnant zones in the anastomoses flow are identified. Time-averaged distributions of wall shear stress and oscillatory shear index obtained for five patient-specific model are compared.

An LES study of secondary motion and wall shear stresses in a pipe bend

Large-eddy simulations (LES) of a single-phase, turbulent flow in a 90° pipe bend are performed at three Reynolds numbers (5300, 27 000, and 45 000) to investigate the correlation between secondary flow motion and wall shear stresses, which is suspected to be a potential mechanism responsible for material erosion. The isothermal flows are validated against available experimental and numerical data first. The snapshot proper orthogonal decomposition (POD) is applied for the medium and high Reynolds number flows to identify the secondary flow motions and the oscillation of the Dean vortices that are found to cause swirl-switching. Distinguished frequencies of the POD time coefficients at Strouhal numbers of 0.25 and 0.28 are identified for Reynolds numbers at 27 000 and 45 000, respectively. Moreover, shear stress on the pipe wall and the associated power spectral density are obtained and shown to have the same oscillating frequency as the swirl-switching.

Computational Assessment of Hemodynamics Vortices Within the Cerebral Vasculature Using Informational Entropy.

Propper assessment of hemodynamic swirling flow patterns, vortices, may help understand the influence of disturbed flow on arterial wall pathophysiology and remodeling. Studies have shown that vortices trigger pathologic cellular changes within the vasculature such as increased inflammation and cellular apoptosis, leading to weakening of the vessel wall indicative of aneurysm development and rupture. Yet many studies qualitatively assess the presence of vortices within the vasculature or assess only their centermost region (critical point analysis) which overlooks the broader characteristics of flow, leading to a narrow view of vortices. This chapter provides a protocol for utilizing commercially available computational fluid dynamic software (ANSYS-FLUENT) to simulate realistic hemodynamic flow patterns, fluid velocity, and wall shear stress in the complex geometry of the cerebral vasculature, as well as an innovative method for assessing flow vortices. This innovative analytic methodology can identify areas of flow vortices and quantify how the broader bulk-flow (opposed to critical point) characteristics change in space and time over the cardiac cycle. Analysis of such flow structures can be used to identify specific characteristics such as vortex stability and the portion of an aneurysmal sac that is dominated by swirling flow, which may be indicative of vascular pathologies.

A 1D–3D Hybrid Model of Patient-Specific Coronary Hemodynamics

Coronary flow is affected by evolving events such as atherosclerotic plaque formation, rupture, and thrombosis, resulting in myocardial ischemia and infarction. Highly resolved 3D hemodynamic data at the stenosis is essential to model shear-sensitive thrombotic events in coronary artery disease. We developed a hybrid 1D-3D simulation framework to compute patient-specific coronary hemodynamics efficiently. A 1D model of the coronary flow is coupled to an image-based 3D model of the region of interest. This framework affords the advantages of reduced-order modeling, decreasing the global computational cost, without sacrificing the accuracy of the quantities of interest. We validated our 1D-3D model against full 3D coronary simulations in healthy and diseased conditions. Our results showed good agreement between the 3D and the 1D-3D models while reducing the computational cost by 40-fold compared to the 3D simulation. The 1D-3D model predicted left/right coronary flow distribution within 3% and provided an accurate estimation of fractional flow reserve and wall shear stress distribution at the stenosis comparable to the 3D simulation. Savings in computational cost may be significant in situations with changing geometry, such as growing thrombosis. Also, this approach would allow quantifying the time-dependent effect of thrombotic growth and occlusion on the global coronary circulation.