Oscillatory Shear Index Values Research Articles

Associations between carotid plaque shape, biomechanical parameters, and ischemic stroke in mild carotid stenosis with a single plaque.

This cross-sectional cohort-comparison observational study investigated the value of high-frame-rate vector flow (V Flow) imaging for evaluating differences in carotid plaque shape and biomechanical parameters in patients with mild stenosis according to a recent history of ipsilateral ischemic stroke. The present study included 352 patients from February 2023 to October 2023, who were categorized as symptomatic or asymptomatic based on a history of recent ischemic stroke and ipsilateral ischemic lesions detected on head computed tomography or magnetic resonance imaging. A Mindray Resona R9 system was used for B-mode ultrasonography and V Flow imaging. The upstream and downstream surfaces of the plaques were examined at the carotid bifurcation for wall shear stress (WSS), oscillatory shear index (OSI), and turbulence index, which performed peri-plaque biomechanical condition. Multivariable logistic regression models were used to determine associations between plaque shape, V Flow parameters, and ischemic stroke. Symptomatic patients exhibited higher WSS values for the upstream and downstream surfaces of carotid plaque, as well as higher OSI and turbulence index values for the downstream surface. Type Ⅲ plaques and higher WSS and OSI values for the downstream surface of the plaque were significantly associated with ischemic stroke. Type Ⅲ plaques were more prevalent in symptomatic patients and demonstrated much higher WSS and OSI values for the downstream plaque surface in both groups. High-frame-rate V Flow imaging could assess peri-plaque biomechanical forces and may provide effective imaging biomarkers for early prediction of ischemic stroke in patients with mild stenosis.

A hemodynamic study of blood flow models on various stent graft configurations during aorto-iliac reconstruction.

To compare the hemodynamic performance of three (Bottom Up non-ballet, Top-Down non-ballet, Top Down ballet) idealized stent graft configurations used during endovascular repair of abdominal aortic aneurysms, under the influence of various rheological models. Ten rheological models are assumed and a commercial finite volume solver is employed for the simulation of blood flow under realistic boundary conditions. An appropriate mesh convergence study is performed and five hemodynamic variables are computed: the time average wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), endothelial cell activation potential and displacement force (DF) for all three configurations. The choice of blood flow model may affect results, but does not constitute a significant determinant on the overall performance of the assumed stent grafts. On the contrary, stent graft geometry has a major effect. Specifically, the Bottom Up non-ballet type is characterized by the least favorable performance presenting the lowest TAWSS and the highest OSI, RRT and ECAP values. On the other hand, the Top Down ballet type presents hemodynamic advantages yielding the highest TAWSS and lowest OSI, RRT and ECAP average values. Furthermore, the ballet type is characterized by the lowest DF, although differences observed are small and their clinical relevance uncertain. The effect of the assumed rheological model on the overall performance of the grafts is not significant. It is thus relatively safe to claim that it is the type of stent graft that determines its overall performance rather than the adopted blood flow model.

Influence of parent vessel feature on the risk of internal carotid artery aneurysm rupture via computational method

In this study, the role of sac section area and parent vessel diameter on the hemodynamic feature of the blood flow in selected internal carotid artery (ICA) aneurysms is comprehensively investigated. The changes of wall shear stress, pressure, and oscillatory shear index (OSI) of blood stream on the vessel for various aneurysms with coiling treatment. To attain hemodynamic factors, computational technique is used for the modeling of non-Newtonian transient blood flow inside the three different ICA aneurysms. Three different saccular models with various Parent vessel mean Diameter is investigated in this study. The achieved outcomes show that increasing the diameter of the parent vessel directly decreases the OSI value on the sac surface. In addition, the mean wall shear stress decreases with the increase of the parent vessel diameter.

Assessing the impact of aneurysm morphology on the risk of internal carotid artery aneurysm rupture: A statistical and computational analysis of endovascular coiling

Computational modeling and investigation have become increasingly useful in assessing the hemodynamic and structural factors that contribute to aneurysm rupture, particularly when conventional clinical tools are inadequate. To this end, we conduct a study of a realistic internal carotid artery (ICA) under various working conditions using computational fluid dynamics. We analyze nine specific real ICA geometries in terms of coiling porosity and blood hematocrit, using a response surface model to evaluate 25 runs across selected geometrical parameters and treatment factors. The computational domain is created using computed tomography data from an actual patient, and we apply proposed boundary conditions to solve three-dimensional transient Navier–Stokes equations. By analyzing these cases, we try to understand how the sac section area, mean radius of the parent vessel, hematocrit, and coiling porosity interact and affect the risk of ICA rupture. We conduct an extensive study of the effects of sac section area and mean radius of the parent vessel on blood hemodynamics, examining several factors and comparing them at the peak systolic time instant, including wall shear stress (WSS), oscillatory shear index (OSI), pressure distributions, and velocity. Our results show that a 12% increase in the mean radius of the parent vessel reduced the maximum OSI value by approximately 50%, while a 120% increase in the sac section area decreases WSS on the aneurysm wall by up to 300%. These findings demonstrate the potential of computational modeling to provide valuable insight into the complex factors that influence aneurysm rupture, especially in cases where traditional clinical tools may be insufficient.

Numerical analysis of hemodynamic parameters in stenosed arteries under pulsatile flow conditions

This research studies the changes in flow patterns and hemodynamic parameters of diverse shapes and sizes of stenosis. Six different shapes and sizes of stenosis are constructed to investigate the variations in hemodynamics as the morphology changes. Changes in shape (trapezoidal and bell-shaped) and sizes of stenosis change the stresses on the walls and their flow patterns. TAWSS and OSI results specify that trapezoidal stenosis exerts greater stress than bell-shaped stenosis. Also, as the length of the trapezoidal stenosis increases, the TAWSS increases, whereas the trend is the opposite for bell-shaped stenosis. Later, this paper also studies different degrees of stenosis extracted from real images. Changes in velocity flow patterns, wall shear stress (WSS), Time-averaged wall shear stress (TAWSS) and Oscillatory shear index (OSI) have been studied for these images. Results illustrate that the peak velocity rises drastically as the stenosis percentage increases. Negative velocity is seen close to the artery's walls, indicating flow separation. This flow separation region is seen throughout the cycle except in the accelerating flow region. An increase in stenosis also increases WSS and TAWSS drastically. Negative WSS is seen downstream of stenosis, indicating flow recirculation. Such negative WSS in the blood vessels also promotes endothelial dysfunction. OSI values greater than 0.2 are seen near the stenosis region, indicating atherosclerosis growth. Regions of high OSI and low TAWSS are also identified, indicating probable regions of plaque development.

Near-wall hemodynamic parameters quantification in in vitro intracranial aneurysms with 7 T PC-MRI

ObjectiveWall shear stress (WSS) and its derived spatiotemporal parameters have proven to play a major role on intracranial aneurysms (IAs) growth and rupture. This study aims to demonstrate how ultra-high field (UHF) 7 T phase contrast magnetic resonance imaging (PC-MRI) coupled with advanced image acceleration techniques allows a highly resolved visualization of near-wall hemodynamic parameters patterns in in vitro IAs, paving the way for more robust risk assessment of their growth and rupture.Materials and methodsWe performed pulsatile flow measurements inside three in vitro models of patient-specific IAs using 7 T PC-MRI. To this end, we built an MRI-compatible test bench, which faithfully reproduced a typical physiological intracranial flow rate in the models.ResultsThe ultra-high field 7 T images revealed WSS patterns with high spatiotemporal resolution. Interestingly, the high oscillatory shear index values were found in the core of low WSS vortical structures and in flow stream intersecting regions. In contrast, maxima of WSS occurred around the impinging jet sites.ConclusionsWe showed that the elevated signal-to-noise ratio arising from 7 T PC-MRI enabled to resolve high and low WSS patterns with a high degree of detail.

Effect of Sac Asymmetry, Neck and Iliac Angle on the Hemodynamic Behavior of Idealized Abdominal Aortic Aneurysm Geometries

Abdominal Aortic Aneurysms (AAAs) are currently treated based on the universal maximum diameter criterion, but other geometric variables may play a role in the risk of rupture. The hemodynamic environment inside the AAA sac has been shown to interact with several biologic processes which can affect prognosis. AAA geometric configuration has a significant impact in the hemodynamic conditions that develop, which has only been recently realized, with implications for rupture risk estimations. We aim to perform a parametric study to evaluate the effect of aortic neck angulation, angle between the iliac arteries and sac asymmetry on the hemodynamic variables of AAAs. This study uses idealized AAA models and it is parametrized in terms of three quantities: the neck angle, φ(o), iliac angle, θ(o), and sac asymmetry, SA(%), each of which accepts three different values, specifically φ=(0o,30o,60o),θ=(40o,60o,80o), and SA=(S,SS,OS) where the sac asymmetry can either be on the same side with respect to neck (SS) or on the opposite side (OS). Time Average Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), Relative Residence Time (RRT) and the velocity profile are calculated for different geometric configurations while the percentage of the total surface area under thrombogenic conditions, using thresholds previously reported in the literature, is also recorded. In case of an angulated neck and a higher angle between iliac arteries, favorable hemodynamic conditions are predicted with higher TAWSS and lower OSI and RRT values. The area under thrombogenic conditions reduces by 16%-46% as the neck angle increases from 0o to 60o, depending on the hemodynamic variable under consideration. The effect of iliac angulation is present but less pronounced with 2.5%-7.5% change between the lower and the higher angle. The effect of sac asymmetry seems to be significant for OSI with a non-symmetrical configuration being hemodynamically favorable, which in the presence of an angulated neck is more pronounced for the OS outline. Favorable hemodynamic conditions develop inside the sac of idealized AAAs with increasing neck and iliac angles. Regarding the sac asymmetry parameter, asymmetrical configurations most often appear advantageous. Concerning the velocity profile the triplet (φ,θ,SA) may affect outcomes under certain conditions and thus should be taken into account when parametrizing the geometric characteristics of AAAs.

Computational assessment of venous anastomosis angles and graft configurations in arteriovenous graft

Arterio-venous grafts are a viable option for hemodialysis as long-term vascular access. The leading cause of Arterio-venous Grafts (AVG) failure is the development of intimal hyperplasia (IH), primarily found in vessel areas with unfavorable hemodynamic conditions. Computational Fluid Dynamics (CFD) is utilized in this study to assess the effect of some geometrical designs at venous anastomosis on these conditions.At first, models with various anastomosis angles are designed. Results represent that the maximum Wall Shear Stress (WSS) in the model with the anastomosis angle of 15° has decreased from 34.07 Pa to 17.48 Pa (48.69%) compared to the conventional model. Moreover, vortices and regions with high WSS at vein anastomosis reduce remarkably.In the second part, to lessen the unfavorable hemodynamic conditions inspired by the rotational blood flow in the aorta, the graft is designed with several cross-sectional ridges to induce a swirl flow. Three essential hemodynamic parameters, including Oscillatory Shear Index (OSI), Time Averaged Wall Shear Stress (TAWSS), and Relative Residence Time (RRT) in pulsating blood flow models, are extracted, and the outcomes are compared to conventional AVG.Finally, according to the results of the previous sections, an optimized model is proposed. Comparing this model with the conventional one illustrates more than 90% decrement in regions related to high OSI values and a 22.84% reduction in RRT values as the main hemodynamic parameters to assess the areas with a high risk of IH development.

Effects of blood hematocrit on performance of endovascular coiling for treatment of middle cerebral artery (MCA) aneurysms: Computational study

Aneurysms with saccular cervical aneurysms are often treated with coiling embolism to prevent rupture and hemorrhage. This study attempted to examine the effects of coiling embolism on blood hemodynamics and bleeding from Middle cerebral artery (MCA) aneurysms. The pulsatile blood stream inside the heart is modeled using computational fluid dynamics by solving Reynolds Average Navier-stocks (RANS) equations. In this study, pressure, oscillatory shear index (OSI), and wall shear stress (WSS) on the sac wall are compared to reveal the high-risk zone at different times during the blood cycle. We also examine the role of coiling porosity in three different conditions of peak systolic blood hematocrit. The WSS value reaches its maximum near the neck of the sac, while the OSI value reaches its maximum near the dome of the aneurysm. Coiling also reduces OSI while having a limited impact on WSS near the neck, according to our results.

Distribution and regional variation of wall shear stress in the curved middle cerebral artery using four-dimensional flow magnetic resonance imaging.

To investigate the distribution and regional variation of wall shear stress (WSS) in the curved middle cerebral artery (MCA) in healthy individuals using four-dimensional (4D) flow magnetic resonance imaging (MRI). A total of 44 healthy participants (18 males; mean ages: 27.16±5.69 years) were included in this cross-sectional study. The WSS parameters of mean, minimum, and maximum values, the coefficient of variation of time-averaged WSS (TAWSSCV), and the maximum values of the oscillatory shear index (OSI) were calculated and compared in the curved proximal (M1) segments. Three cross-sectional planes were selected: the location perpendicular to the beginning of the long axis of the curved M1 segment of the MCA (proximal section), the most curved M1 location (curved M1 section), and the location before the insular (M2) segment bifurcation (distal section). The WSS and OSI parameters of the proximal, curved, and distal sections of the curved M1 segment were compared, including the inner and outer curvatures of the curved M1 section. Of the curved M1 segments, the curved M1 section had significantly lower minimum TAWSS values than the proximal (P=0.031) and distal sections (P=0.002), and the curved M1 section had significantly higher maximum OSI values than the distal section (P=0.001). The TAWSSCV values at the curved M1 section were significantly higher than the proximal (P=0.001) and distal sections (P<0.001). At the curved M1 section, the inner curvature showed a significantly lower minimum TAWSS (P=0.013) and higher maximum OSI values (P=0.002) than the outer curvature. There are distribution variation of WSS and OSI parameters at the curved M1 section of the curved MCA, and the inner curvature of the curved M1 section has the lowest WSS and highest OSI distribution. The local hemodynamic features of the curved MCA may be related to the predilection for atherosclerotic plaque development.

Euler-Lagrange numerical simulation of improved magnetic drug delivery in a three-dimensional CT-based carotid artery bifurcation

Background and objectiveMagnetic drug targeting (MDT) is a promising method to improve the therapy efficiency for cardiovascular diseases (CVDs) and cancers. In MDT, therapeutic agents are bonded to superparamagnetic iron oxide nanoparticle (SPION) cores and then are guided toward the damaged tissue through a magnetic field. Fundamentally, it's vital to steer the SPIONs to the desired location to increase the capture efficiency at the target lesion. Hence, the present study aims to enhance the drug delivery to the desired branch in a carotid bifurcation. Besides, it is tried to decrement the particles' entry to the unwanted outlet by using four different magnet configurations (with a maximum magnetic flux density of 0.4 T) implanted adjacent to the artery wall. Also, the effect of particles’ diameter –ranging from 200 nm to 2 µm– on the drug delivery performance is studied in the four cases. MethodsThe Eulerian-Lagrangian approach with one-way coupling is employed for numerical simulation of the problem using the finite element method (FEM). The dominant forces acting on particles are drag and magnetophoretic. A computed tomography (CT) model of the carotid bifurcation is adopted to have a 3D realistic geometry. The blood flow is considered to be laminar, incompressible, pulsatile, and non-Newtonian. Boundary conditions are applied using the three-element Windkessel equation. ResultsResults are presented in terms of velocity, pressure, magnetic field flux density, wall shear stress, and streamlines. Also, the number of particles in each direction is presented for the four studied cases. The results show that using proper magnets configurations makes it possible to guide more particles to the desired branch (up to 4%) while preventing particles from entering the unwanted branch (up to 13%). By defining connectivity between oscillatory shear index (OSI) value and magnetic drug delivery efficacy, it becomes clear that places with lower OSI values are more proper to place the magnets than areas with higher OSI values. ConclusionsIt was observed that increasing the diameter of particles does not necessarily result in a higher drug delivery efficiency. The configuration of the magnets and the size of particles are the main affecting parameters that should be chosen precisely to meet the most efficient drug delivery performance.Magnetic drug targeting (MDT) is a promising method to improve the therapy efficiency for cardiovascular diseases (CVDs) and cancers. Fundamentally, it's vital to steer the superparamagnetic iron oxide nanoparticles (SPIONs) to the target lesion location to increase the capture efficiency. Hence, the present study aims to enhance the drug delivery to the desired branch in a 3D carotid bifurcation. Besides, it is tried to decrement the particles' entry to the unwanted outlet by using four different magnet configurations implanted adjacent to the artery wall.The Eulerian-Lagrangian approach with one-way coupling is employed for numerical simulation of the problem using the finite element method (FEM). The dominant forces acting on particles are drag and magnetophoretic. The blood flow is laminar, incompressible, pulsatile, and non-Newtonian.The results show that it is possible to guide more particles to the desired branch (up to 4%) while preventing particles from entering the unwanted branch (up to 13%). By defining connectivity between oscillatory shear index (OSI) value and magnetic drug delivery efficacy, it becomes clear that places with lower OSI values are more proper to place the magnets than areas with higher OSI values.

The Correlation Between Wall Shear Stress and Plaque Composition in Advanced Human Carotid Atherosclerosis.

The role of wall shear stress (WSS) in atherosclerotic plaque development is evident, but the relation between WSS and plaque composition in advanced atherosclerosis, potentially resulting in plaque destabilization, is a topic of discussion. Using our previously developed image registration pipeline, we investigated the relation between two WSS metrics, time-averaged WSS (TAWSS) and the oscillatory shear index (OSI), and the local histologically determined plaque composition in a set of advanced human carotid plaques. Our dataset of 11 carotid endarterectomy samples yielded 87 histological cross-sections, which yielded 511 radial bins for analysis. Both TAWSS and OSI values were subdivided into patient-specific low, mid, and high tertiles. This cross-sectional study shows that necrotic core (NC) size and macrophage area are significantly larger in areas exposed to high TAWSS or low OSI. Local TAWSS and OSI tertile values were generally inversely related, as described in the literature, but other combinations were also found. Investigating the relation between plaque vulnerability features and different combinations of TAWSS and OSI tertile values revealed a significantly larger cap thickness in areas exposed to both low TAWSS and low OSI. In conclusion, our study confirmed previous findings, correlating high TAWSS to larger macrophage areas and necrotic core sizes. In addition, our study demonstrated new relations, correlating low OSI to larger macrophage areas, and a combination of low TAWSS and low OSI to larger cap thickness.

Analysis of the Optimum Tapering Angle in Microanastomosis Using Computational Fluid Dynamics.

In free flap transfer, size discrepancy between the vascular pedicle and recipient vessel can create a problem for microsurgeons and sometimes induces postoperative thrombus formation. When there is a major difference between the diameters of the vascular pedicle and the recipient vessel, the larger vessel is often tapered to perform the anastomosis properly. However, the decision on the tapering angle used depends mostly on the operator's experience. In this study, computational fluid dynamics (CFD) was used to investigate the optimum tapering angle. Using ANSYS ICEM 16.0 (ANSYS Japan, Tokyo, Japan), simulated vessels of diameters 1.5 mm and 3.0 mm were designed and then used to produce four anastomosis models with the 3.0-mm vessel tapered at angles of 15º, 30º, 60º, and 90º (no tapering). Venous perfusion with a mean value of 13.0 mL/min was simulated, and this was passed through the four anastomosis models in both the forward direction (F), from the smaller to the larger vessel, and the retrograde direction (R), from the larger to the smaller vessel. The velocity, wall shear stress (WSS), and oscillatory shear index (OSI) were measured in these eight patterns and then analyzed using OpenFOAM version 5. The decrease in velocity was limiting. The WSS was greater in the R direction than the F direction at every tapering angle. The OSI also tended to be almost the same in the F direction, and lower at smaller tapering angles in the R direction. And, it was greater in the F direction than in the R direction at every tapering angle. The OSI values for 15º and 30º were almost identical in the R direction. The risk of thrombus formation is thought to be lower when tapering is used for anastomosis if the direction of flow is from the larger to the smaller vessel, rather than vice versa. These results also suggest that the optimum tapering angle is approximately 30º in both directions.

Predicting the onset of consequent stenotic regions in carotid arteries using computational fluid dynamics

Carotid arteries are the major blood vessels that carry oxygenated blood to the brain and face. Carotid artery disease is characterized by the narrowing of the carotid arteries due to plaque buildup at the arterial walls, leading to major consequences such as brain stroke and death. Hemodynamics such as wall shear stress (WSS) and velocity distribution can be employed to investigate the severity and location of stenosis in the carotid arteries. Furthermore, the potential of stenosis in other regions along the carotid arteries is affected by local variations in hemodynamics. To investigate other potential high-risk regions, a comprehensive blood flow model was utilized through a reconstructed three-dimensional patient-specific geometry with realistic boundary conditions. The developed model was numerically simulated and validated. The results indicated that hemodynamics can be successfully used to investigate the degree of stenosis severity and location. Two different locations along the carotid artery were examined. At location 1 (near the artery bifurcation) of the common carotid artery, the WSS increased from 11 Pa in the case of 42% stenosis to 27 Pa in the case of 61% stenosis and 263 Pa for 84% stenosis. Such values significantly decreased at location 2 (far from the artery bifurcation) because of the increasing distance from the artery bifurcation. In addition, the maximum value of the oscillatory shear index (OSI) downstream of the stenosis throat reached 0.5, and the outlet mass flow rate changed significantly with varying stenosis location. Carotid artery stenosis affects the artery bifurcation, which appears to be at high risk because of thrombus and arterial wall rupture, which are clearly indicated by the WSS and OSI values in this region. The current findings support the efficient use of a computational fluid dynamics approach for the diagnosis and prediction of carotid artery stenosis.

Wall shear stress gradient is independently associated with middle cerebral artery aneurysm development: a case-control CFD patient-specific study based on 77 patients

BackgroundPreviously published computational fluid dynamics (CFD) studies regarding intracranial aneurysm (IA) formation present conflicting results. Our study analysed the involvement of the combination of high wall shear stress (WSS) and a positive WSS gradient (WSSG) in IA formation.MethodsWe designed a case-control study with a selection of 38 patients with an unruptured middle cerebral artery (MCA) aneurysm and 39 non-aneurysmal controls to determine the involvement of WSS, oscillatory shear index (OSI), the WSSG and its absolute value (absWSSG) in aneurysm formation based on patient-specific CFD simulations using velocity profiles obtained from transcranial colour-coded sonography.ResultsAmong the analysed parameters, only the WSSG had significantly higher values compared to the controls (11.05 vs − 14.76 [Pa/mm], P = 0.020). The WSS, absWSSG and OSI values were not significantly different between the analysed groups. Logistic regression analysis identified WSS and WSSG as significant co-predictors for MCA aneurysm formation, but only the WSSG turned out to be a significant independent prognosticator (OR: 1.009; 95% CI: 1.001–1.017; P = 0.025). Significantly more patients (23/38) in the case group had haemodynamic regions of high WSS combined with a positive WSSG near the bifurcation apex, while in the control group, high WSS was usually accompanied by a negative WSSG (14/39). From the analysis of the ROC curve for WSSG, the area under the curve (AUC) was 0.654, with the optimal cut-off value −0.37 Pa/mm. The largest AUC was recognised for combined WSS and WSSG (AUC = 0.671). Our data confirmed that aneurysms tend to form near the bifurcation apices in regions of high WSS values accompanied by positive WSSG.ConclusionsThe development of IAs is determined by an independent effect of haemodynamic factors. High WSS impacts MCA aneurysm formation, while a positive WSSG mainly promotes this process.

Effects of the Haemodynamic Stimulus on the Location of Carotid Plaques Based on a Patient-Specific Mechanobiological Plaque Atheroma Formation Model.

In this work, we propose a mechanobiological atheroma growth model modulated by a new haemodynamic stimulus. To test this model, we analyse the development of atheroma plaques in patient-specific bifurcations of carotid arteries for a total time of 30 years. In particular, eight geometries (left or right carotid arteries) were segmented from clinical images and compared with the solutions obtained computationally to validate the model. The influence of some haemodynamical stimuli on the location and size of plaques is also studied. Plaques predicted by the mechanobiological models using the time average wall shear stress (TAWSS), the oscillatory shear index (OSI) and a new index proposed in this work are compared. The new index predicts the shape index of the endothelial cells as a combination of TAWSS and OSI values and was fitted using data from the literature. The mechanobiological model represents an evolution of the one previously proposed by the authors. This model uses Navier-Stokes equations to simulate blood flow along the lumen in the transient mode. It also employs Darcy's law and Kedem-Katchalsky equations for plasma and substance flow across the endothelium using the three-pore model. The mass balances of all the substances that have been considered in the model are implemented by convection-diffusion-reaction equations, and finally the growth of the plaques has been computed. The results show that by using the new mechanical stimulus proposed in this study, prediction of plaques is, in most cases, better than only using TAWSS or OSI with a minimal and maximal errors on stenosis ratio of 2.77 and 32.89 %, respectively. However, there are a few geometries in which haemodynamics cannot predict the location of plaques, and other biological or genetic factors would be more relevant than haemodynamics. In particular, the model predicts correctly eleven of the fourteen plaques presented in all the geometries considered. Additionally, a healthy geometry has been computed to check that plaque is not developed with the model in this case.

Influence of aneurysmal aortic root geometry on mechanical stress to the aortic valve leaflet.

While mechanical stress caused by blood flow, e.g. wall shear stress (WSS), and related parameters, e.g. oscillatory shear index (OSI), are increasingly being recognized as key moderators of various cardiovascular diseases, studies on valves have been limited because of a lack of appropriate imaging modalities. We investigated the influence of aortic root geometry on WSS and OSI on the aortic valve (AV) leaflet. We applied our novel approach of intraoperative epi-aortic echocardiogram to measure the haemodynamic parameters of WSS and OSI on the AV leaflet. Thirty-six patients were included, which included those who underwent valve-sparing aortic root replacement (VSARR) with no significant aortic regurgitation (n = 17) and coronary artery bypass graft (CABG) with normal AV (n = 19). At baseline, those who underwent VSARR had a higher systolic WSS (0.52 ± 0.12 vs. 0.32 ± 0.08 Pa, respectively, P < 0.001) and a higher OSI (0.37 ± 0.06 vs. 0.29 ± 0.04, respectively, P < 0.001) on the aortic side of the AV leaflet than those who underwent CABG. Multivariate regression analysis revealed that the size of the sinus of Valsalva had a significant association with WSS and OSI. Following VSARR, WSS and OSI values decreased significantly compared with the baseline values (WSS: 0.29 ± 0.12 Pa, P < 0.001; OSI: 0.26 ± 0.09, P < 0.001), and became comparable to the values in those who underwent CABG (WSS, P = 0.42; OSI, P = 0.15). Mechanical stress on the AV gets altered in correlation with the size of the aortic root. An aneurysmal aortic root may expose the leaflet to abnormal fluid dynamics. The VSARR procedure appeared to reduce these abnormalities.

Retrograde branched extension limb assembling stent of pararenal abdominal aortic aneurysm: A longitudinal hemodynamic analysis for stent graft migration.

Pararenal abdominal aortic aneurysms (PRAAAs) are a life-threatening disease, and hemodynamic analysis may provide greater insight into the effectiveness and long-term outcomes of endovascular aneurysm repair (EVAR). However, the lack of patient-specific boundary conditions on the periphery compromises the accuracy. Windkessel (WK) boundary conditions coupled to hemodynamic follow-up models of a PRAAA patient, aims to provide insights into the link between hemodynamics and poor prognosis. One PRAAA patient underwent EVAR and reintervention after one branch of stent-graft (SG) had migrated. Totally five computational follow-up models were studied. Patient-specific flow data acquired via ultrasound were used to define the boundary conditions in the ascending aorta and the following three branches. Coupled zero-dimensional WK models representing the distal vasculature were used to define the outlet boundary conditions under the abdomen. Flow divisions of the main SG branches were 40.7% and 24.7%, respectively. Time-averaged wall shear stress and oscillatory shear index (OSI) increased at the junction connected the SG branch and the stent leading to the right common iliac artery (RCIA) where the stent migrated. The OSI and relative residence time (RRT) value in superior mesenteric artery increased notably after the migration, the RRT continuously increased following the reintervention. Unbalanced flow, resulting in locally high-speed flow, high WSS and OSI might significantly affect stent stability. Results suggest that diameters and interconnection design of stents in complex cases should take the flow division into consideration and computational simulations might be considered as a tool for intervention protocol design.

Evaluation of the Influence of Wall Shear Stress Features from Newly Fashioned Arteriovenous Fistulae on Endothelial Cell Phenotypes In Vitro

Objective: Patency rates for autogenous arteriovenous fistulae (AVFs) range between 60% and 80% at two years. The wall shear stress (WSS) is the frictional force per unit area exerted at the interface of the flowing blood and the endothelium and is a potent stimulus capable of evoking differential phenotypes in endothelial cells (ECs). The aim of this study was to investigate the influence of WSS on EC phenotypes. Methods: The intraluminal pressures and waveforms from the arterial and venous limbs of 14 newly fashioned human AVFs (four radiocephalic, 10 brachiocephalic) were measured using a microcatheter transducer and pull through technique. Human umbilical vein endothelial cells (HUVECs) were exposed for 24 hours to 10 idealised physiological waveforms (using calculations from in vivo experiments) with WSS peak magnitude 0.5 – 2.5 Pa, temporal wall shear stress gradient (t-WSSG) from 2 to 20 Pa/s, and from 0 to 0.5 of the oscillatory shear index value. Differential protein and gene expression was evaluated using reverse transcription polymerase chain reaction, western blot, and immunofluorescence staining. Results: In vitro results indicate that WSS waveforms with a peak magnitude of 1.5 or 2.5 Pa can induce a protective phenotype in ECs in culture (Krüppel-like factor-2 (KLF-2), KLF-4, Interleukin-8 (IL-8), and vascular cell adhesion molecule -1 (VCAM-1) expression). By presenting a reverse phase or decreasing time averaged WSS of the waveforms with a peak of 1.5 or 2.5 Pa, the flow induced protective effect is maintained. A WSS peak of 1.5 Pa is shown to be sufficient to induce protective pathways. Pro-inflammatory gene analysis showed no differences in the expression of two subunits of nuclear factor kappa B. Conclusion: The differential effects of WSS profiles can induce protective or pro-inflammatory EC profiles. These results suggest that geometrical variations may influence AVF patency rates and outcomes.

Fluid structure interaction study of stenosed carotid artery considering the effects of blood pressure

Atherosclerosis is the most common cardiovascular disease (CVD) causing increased morbidity. Although atherosclerosis is a general disease involving several factors, it preferentially affects the wall of the vessel bifurcations. The use of advanced Computational Fluid Dynamics (CFD) techniques has the potential to shed more light in the further understanding of the causes of the disease and perhaps in its early diagnosis. In this work, a three-dimensional (3D) Fluid Structure Interaction (FSI) study was carried out for a patient specific carotid artery. By considering physiological conditions, first the normal and then with hypertension disease, haemodynamic parameters were evaluated to better understand the genesis and progression of atherosclerotic plaques in the carotid artery bifurcation. Two-way FSI was performed by applying a fully implicit second-order backward Euler differencing scheme using commercial software ANSYS and ANSYS CFX (version 19.0). Arbitrary Lagrangian–Eulerian (ALE) formulation was employed to calculate the arterial response by using the temporal blood response. Due to arterial bifurcation, obvious velocity reduction and backflow formation were observed which decreased shear stress and made it oscillatory at the starting point of the internal carotid artery near the carotid sinus, which resulted in low shear stress. Oscillatory Shear Index (OSI) signifies oscillatory behaviour of artery wall shear stress. By using anatomically realistic 3D geometry and representative physiological conditions, the results obtained for shear stress are more acceptable. Comparison of the results of this study with those in the published literature shows that the regions with low wall shear stress and with OSI value greater than 0.3 pose potential risk to the development of plaques. It was observed that haemodynamics of the carotid artery was very much affected by the geometry and flow conditions. Furthermore, regions of relatively low wall shear stress were observed post stenosis, which is a known cause of plaque development and progression.