Evaluation Of Wall Shear Stress Research Articles

Understanding haemolysis in polysulfone and glass fibre membranes for blood separation

This preliminary study aims to understand the mechanism of haemolysis in the process of blood separation in porous membranes in a confined scope. Two typical membranes (polysulfone and glass fibre membranes) were chosen as the representatives for the two different (vertical and lateral) blood separation directions. The wall shear stress (WSS) applied on the RBCs and the effects of the morphology of the pores in the membranes on the integrity of RBCs, were investigated to find the main reason for inducing the release of intracellular components into the plasma occurring as haemolysis. With the evaluation of WSS in the two membranes, it has been found that the impact of WSS is insufficient as a single factor causing haemolysis. Based on the morphology of the internal structures of the two porous membranes characterised by SEM imaging combined with the quantitative analysis on the number of sharp ends in the membranes, it has been shown that haemolysis is mainly caused by the puncture on the RBCs because of the sharp ends of the fibrous structure in the membranes. The membranes having more sharp ends show a higher level of haemolysis. The haemolysis during blood separation has been characterised using UV–vis spectrophotometry.

Experimental evaluation of wall shear stress in an elastic cerebral aneurysm model

Experimental evaluation of wall shear stress in an elastic cerebral aneurysm model

Formula neiterativnog modela zida za neravnotežne tokove graničnog sloja

A novel non-iterative (explicit) formulation of generalized wall functions that applies to equilibrium and non-equilibrium boundary layer flows was proposed. The proposed formulation uses a set of variables that are more useful for computational fluid dynamics codes as they allow for calculating wall shear stress without an iterative procedure. In addition, an explicit form of the formulation was provided that applies to wall models with and without pressure gradients. The new variable transformation casts the generalizedwall function into a new form that simplifies the implementation and evaluation of wall-shear stress in computational codes.

Computational Evaluation of Wall Shear Stress Experienced by Endothelial Tip Cells along Capillary Sprouts

Shear stress is commonly implicated as a regulator of angiogenesis. However, critical questions remain unanswered. Do endothelial cells within a capillary sprout lumen experience shear stress? Can tip cells that extend past the sprout lumen experience shear stress? A full understanding of how shear stresses influence endothelial cell phenotype and function during angiogenesis requires the identification of local stress distribution along capillary sprouts. However, the actual shear stress magnitudes experienced by endothelial cells remain unknown. Motivated by the hypothesis that endothelial tip cells can experience physiological shear stress, the objective of this study was to estimate shear stress magnitudes due to local interstitial flow along endothelial tip cells that extend past capillary sprout lumens. A computational fluid dynamics model was used to estimate flows within a blind-ended vessel, transendothelial flow across the vessel wall, and flow within the surrounding perivascular space. The two-dimensional axisymmetric model consisted of four regions: vessel lumen, vessel wall, perivascular space, and interstitium. The vessel wall was assumed to be porous media with 0.3 μm thickness. Blood plasma was represented as an incompressible Newtonian fluid with density and viscosity equal to 1050 kg/m3 and 1.2 cP, respectfully. Shear stresses along the wall of the tip cell extending past the lumen were calculated for varying sprout lengths (50, 200, and 400 μm), perivascular space channel width (1, 4, and 9 μm), and hydraulic conductivities (1.35 and 6.75 x10-10 ms-1 Pa-1). Model parameters and geometric dimensions were selected based on previously reported literature values. Velocity profiles confirmed transmural flow across the vessel wall, nearly parabolic flow within the perivascular space, and velocity gradients along the tip cell. Increasing sprout length, increasing permeability, and decreasing perivascular space increased shear stress values with the perivascular space parameter being the major influencer. Maximum shear stresses along tip cells were consistently higher than the stresses within the sprout lumen. Wall shear stresses within the lumen ranged from 0.02 to 0.52 dyne/cm2 at the sprout entrance and linearly decreased to near zero along the sprout length. Tip cell wall shear stress due to interstitial flow ranged from 0.19 to 4.65 dyne/cm2. The results suggest that wall shear stress values along tip cells can reach physiological relevant values depending on parameter combinations. Our computational estimates motivate new questions related to whether increased shear stresses along tip cells versus luminal cells contribute phenotypic and function signatures of tip cells.

Towards quantitative evaluation of wall shear stress from 4D flow imaging

Wall shear stress (WSS) is a relevant hemodynamic indicator of the local stress applied on the endothelium surface. More specifically, its spatiotemporal distribution reveals crucial in the evolution of many pathologies such as aneurysm, stenosis, and atherosclerosis. This paper introduces a new solution, called PaLMA, to quantify the WSS from 4D Flow MRI data. It relies on a two-step local parametric model, to accurately describe the vessel wall and the velocity-vector field in the neighborhood of a given point of interest. Extensive validations have been performed on synthetic 4D Flow MRI data, including four datasets generated from patient specific computational fluid dynamics simulations on carotids. The validation tests are focused on the impact of the noise component, of the resolution level, and of the segmentation accuracy concerning the vessel position in the context of complex flow patterns. In simulated cases aimed to reproduce clinical acquisition conditions, the WSS quantification performance reached by PaLMA is significantly higher (with a gain in RMSE of 12 to 27%) than the reference one obtained using the smoothing B-spline method proposed by Potters et al. (2015) method, while the computation time is equivalent for both WSS quantification methods.

The effects of age at correction of aortic coarctation and recurrent obstruction on adolescent patients: MRI evaluation of wall shear stress and pulse wave velocity

BackgroundCoarctation patients before curative reconstruction are exposed to abnormal flow patterns which potentially could cause wall deterioration. This study evaluated the effect of age at correction on the pulse wave velocity (PWV) and peak wall shear stress (WSS) in adolescent patients with corrected coarctation. Effects of valve morphology and presence of reobstruction were also evaluated.MethodsTwenty-one patients aged 13.7 ± 2.6 years (mean ± standard deviation) were included (bicuspid aortic valve, n = 14; reobstruction, n = 9). Mean age at correction was 1.0 ± 1.8 years. PWV was determined from two high-temporal through-plane phase-contrast magnetic resonance imaging (MRI) acquisitions, for two segments: ascending aorta plus aortic arch and descending aorta. WSS was determined from four-dimensional flow MRI. Peak WSS over five systolic phases was determined for ascending aorta, aortic arch, and descending aorta.ResultsPatients with tricuspid aortic valve showed a significant correlation between the age at correction and descending aorta PWV (rs = 0.80, p = 0.010). Significant differences were found between patients without and with reobstruction for peak WSS in the aortic arch (3.9 ± 1.3 Pa versus 6.5 ± 2.2 Pa, respectively; p = 0.003) and descending aorta (5.0 ± 1.3 Pa versus 6.7 ± 1.1 Pa, respectively; p = 0.005).ConclusionsA prolonged period of abnormal haemodynamic exposure may result in increased aortic wall stiffening. The increased peak WSS as results of a reobstruction possibly promotes different disease progression, which endorse longitudinal follow-up examination of corrected coarctation patients.

Clinical evaluation of wall shear stress by ultrafast vector flow imaging in carotid atherosclerotic stenosis

Carotid plaque vulnerability assessment is an important factor in guiding the decision to perform carotid endarterectomy in case of asymptomatic stenosis. Ultrafast Ultrasound Imaging (UUI) offers the possibility of evaluating local flow velocities over an entire 2D image, allowing access to measure the wall shear stress (WSS). Our objective was to evaluate the feasibility of WSS measurement in a prospective series of patients with carotid stenosis. We used a linear probe (7.5 MHz, SuperSonic Imagine©). UUIacquisitions last 600 ms with 3 tilted plane waves for an effective frame rate of 5000 Hz. We evaluated the flow velocity in 5 areas of the carotid wall: common carotid artery (1), plaque ascent (2), peak (3), descent (4), and internal carotid artery (5) ( Figure 1 ). WSS was computed with the vector field speed. Shear stress measurement method was validated using a laminar flow phantom with laminar flow. Good correlation was found between in vitro measurement and the theoretical WSS values (R2 = 0.95; P < 0.001). 25 patients were included (mean age: 72 ± 5 years), with a mean percentage of stenosis of 75 ± 12% (NASCET). The maximum WSS value over one cardiac cycle follows the shape of the plaque with a progressive increase to a maximum value at the peak (2.12 ± 1.27 Pa). The post-stenotic descent zone has the lowest shear stress (0.57 ± 0.39 Pa), lower than the WSS values in the healthy zone (1.02 ± 0.36 Pa for the common carotid and 0.68 ± 0.39 Pa for the internal carotid artery) ( Figure 1 ). This method allowed the local and direct evaluation of the plaque's wall shear stress. Unlike the global evaluation of speed using conventional Doppler, these measurements make it possible to better characterize the haemodynamic conditions to better identify areas of vulnerability.

Experimental evaluation of wall shear stress in an elastic wall cerebral aneurysm model

Experimental evaluation of wall shear stress in an elastic wall cerebral aneurysm model

Experimental evaluation of wall shear stress in elastic cerebral aneurysm model

Experimental evaluation of wall shear stress in elastic cerebral aneurysm model

Experimental evaluation of wall shear stress in a double contraction nozzle using a water mock-up of a liquid Li target for an intense fusion neutron source

Herein, the wall shear stress in a double contraction nozzle has been evaluated experimentally to produce a liquid lithium (Li) target as a beam target for intense fusion neutron sources such as the International Fusion Materials Irradiation Facility (IFMIF), the Advanced Fusion Neutron Source (A-FNS), and the DEMO Oriented Neutron Source (DONES). The boundary layer thickness and wall shear stress are essential physical parameters to understand erosion–corrosion by the high-speed liquid Li flow in the nozzle, which is the key component in producing a stable Li target. Therefore, these parameters were experimentally evaluated using an acrylic mock-up of the target assembly. The velocity distribution in the nozzle was measured by a laser-doppler velocimeter and the momentum thickness along the nozzle wall was calculated using an empirical prediction method. The resulting momentum thickness was used to estimate the variation of the wall shear stress along the nozzle wall. Consequently, the wall shear stress was at the maximum in the second convergent section in front of the nozzle exit.

A Patient-Specific Study Investigating the Relation between Coronary Hemodynamics and Neo-Intimal Thickening after Bifurcation Stenting with a Polymeric Bioresorbable Scaffold

We present an application of a validated reconstruction methodology for the comparison between patient-specific hemodynamics and neo-intimal thickening at nine months from the intervention. (1) Background: Coronary bifurcation stenting alters the vessel geometry, influencing the local hemodynamics. The evaluation of wall shear stress (WSS) relies on the application of computational fluid dynamics to model its distribution along the coronary tree. The endothelium actively responds to WSS, which triggers eventual cell proliferation to cover the stent struts. (2) Methods: Baseline optical coherence tomography and angiographic data were combined to reconstruct a patient-specific coronary bifurcation with an implanted bioresorbable scaffold and to simulate the hemodynamics. Results were linked with the neo-intimal thickening after nine months from the intervention. (3) Results: Blood velocity patterns were disrupted at the bifurcation due to the presence of the stent. It was observed that 55.6% of the scaffolded lumen surface was exposed to values of time-averaged WSS lower than 0.4 Pa. Follow-up images showed a luminal narrowing of 19% in the main branch. There was also a complete coverage in 99% of struts. (4) Conclusions: This approach provided valuable complementary information that might improve the clinical outcomes in this subset of coronary diseases.

P6407A new method for the correct evaluation of wall shear stress in bifurcations: fusion of three-dimensional angiography and two-vessel OCT

P6407A new method for the correct evaluation of wall shear stress in bifurcations: fusion of three-dimensional angiography and two-vessel OCT

Hemodynamic characteristics of hyperplastic remodeling lesions in cerebral aneurysms.

Background & purposeHyperplastic remodeling (HR) lesions are sometimes found on cerebral aneurysm walls. Atherosclerosis is the results of HR, which may cause an adverse effect on surgical treatment for cerebral aneurysms. Previous studies have demonstrated that atherosclerotic changes had a correlation with certain hemodynamic characteristics. Therefore, we investigated local hemodynamic characteristics of HR lesions of cerebral aneurysms using computational fluid dynamics (CFD).MethodsTwenty-four cerebral aneurysms were investigated using CFD and intraoperative video recordings. HR lesions and red walls were confirmed on the intraoperative images, and the qualification points were determined on the center of the HR lesions and the red walls. The qualification points were set on the virtual operative images for evaluation of wall shear stress (WSS), normalized WSS (NWSS), oscillatory shear index (OSI), relative residence time (RRT), and aneurysm formation indicator (AFI). These hemodynamic parameters at the qualification points were compared between HR lesions and red walls.ResultsHR lesions had lower NWSS, lower AFI, higher OSI and prolonged RRT compared with red walls. From analysis of the receiver-operating characteristic curve for hemodynamic parameters, OSI was the most optimal hemodynamic parameter to predict HR lesions (area under the curve, 0.745; 95% confidence interval, 0.603–0.887; cutoff value, 0.00917; sensitivity, 0.643; specificity, 0.893; P<0.01). With multivariate logistic regression analyses using stepwise method, NWSS was significantly associated with the HR lesions.ConclusionsAlthough low NWSS was independently associated with HR lesions, OSI is the most valuable hemodynamic parameter to distinguish HR lesions from red walls.

Phase-contrast magnetic resonance imaging for the evaluation of wall shear stress in the common carotid artery of a spontaneously hypertensive rat model at 7 T: Location-specific change, regional distribution along the vascular circumference, and reproducibility analysis

PurposeTo measure wall shear stress (WSS) in the common carotid arteries (CCA) of a spontaneously hypertensive rat (SHR) model and a normotensive Wistar Kyoto rat (WKY) model by 2D phase-contrast magnetic resonance imaging (PC-MRI). Materials and methodsPC-MRI was performed on 7 SHR and 7 WKY at ages of 4 and 7months at a 7T scanner. Images in the middle CCA (CCAmid) and in the bifurcation of CCA (CCAbifur) were acquired. The WSS values for differentiating characteristics between two models were calculated. Further, its location-specific change, regional distribution along the CCA circumference, and the reproducibility were evaluated. ResultsIn the 4-month-old rats, SHR showed lower temporal averaged WSS (WSSavg) and peak systolic WSS (WSSs) in the CCAbifur in comparison with WKY (WSSavg: 0.95±0.18 vs. 1.30±0.36N/m2 (P<0.01); WSSs: 1.68±0.70 vs. 3.22±2.49N/m2 (P<0.05)). We observed the same trends in the 7-month-old rats. In the SHR model, the WSSavg was lower in the CCAbifur than in the CCAmid. The regional distribution of WSSavg along the circumference of CCA showed lower values in WKY, particularly in posterior segments of CCAbifur. The intra-observer, intra-scan and inter-scan reproducibility was acceptable and the disagreements were ranged from −0.05 to 0.06N/m2. ConclusionThis study evaluated WSS in SHR and WKY models by 2D PC-MRI. High reproducibility analyses further indicated the reliability of measurements of WSS in the CCA of SHR and WKY models using PC-MRI at 7T.

Optical Coherence Tomography for Patient-specific 3D Artery Reconstruction and Evaluation of Wall Shear Stress in a Left Circumflex Coronary Artery

Image-based computational models for quantifying hemodynamic indices in stented coronary arteries often employ biplane angiography and intravascular ultrasound for 3D reconstruction. Recent advances in guidewire simulation algorithms and the rise of optical coherence tomography (OCT) suggest more precise coronary artery reconstruction may be possible. We developed a patient-specific method that combines the superior resolution of OCT with techniques for imaging wire pathway reconstruction adopted from graph theory. The wire pathway with minimum bending energy was determined by applying a shortest path algorithm to a graph representation of the artery based on prior studies indicating a wire adopts the straightest configuration within a tortuous vessel. Segments from OCT images are then registered orthogonal to the wire pathway using rotational orientation consistent with geometry delineated by computed tomography (CT). To demonstrate applicability, OCT segments within the stented region were combined with proximal and distal CT segments and imported into computational fluid dynamics software to quantify indices of wall shear stress (WSS). The method was applied to imaging data of a left circumflex artery with thrombus acquired immediately post-stenting and after a 6-month follow-up period. Areas of stent-induced low WSS returned to physiological levels at follow-up, but correlated with measurable neointimal thickness in OCT images. Neointimal thickness was negligible in areas of elevated WSS due to thrombus. This novel methodology capable of reconstructing a stented coronary artery may ultimately enhance our knowledge of deleterious hemodynamic indices induced by stenting after further investigation in a larger patient population.

Four-Dimensional Flow Magnetic Resonance Imaging With Wall Shear Stress Analysis Before and After Repair of Aortopulmonary Fistula

We used 4D flow magnetic resonance imaging1 to evaluate a 34-year-old man with a complicated course after aortic coarctation repair including development of an aortopulmonary fistula. Our initial 4D flow study (Figure 1) reveals abnormal vortical-type flow in the aneurysmal distal aortic arch. Evaluation of wall shear stress calculated from near-wall velocity gradients using proprietary software ( flow tool , University of Freiburg, Germany; software is experimental and not FDA approved)2 demonstrates skewing of higher shear values along the posterior and left lateral aortic arch, just upstream of a pseudoaneurysm. Figure 1. A 34-year-old man with complicated course status after aortic coarctation repair. A, 3D contrast-enhanced magnetic resonance imaging that demonstrates an aneurysm of the distal aortic arch extending …

PIV Measurement of Pulsatile Flow in a Y-shape Bifurcation and Evaluatoin of Wall Shear Stress

The mechanism of atherosclerosis has not been clarified yet. It is known, however, that the blood flow and the vessel wall stress might have more or less impact on its occurring. In the present study, in order to obtain the information of pulsatile flow in the arterial Y-shape bifurcation, where the atherosclerosis selectively occurs, the PIV (Particle Image Velocimetry) measurement has been carried out for Y-tube solid and elastic models. The results of velocity distributions on the centered plane are described for one pulsatile flow pattern, and the difference of flow patterns between solid and elastic models is discussed. Then the validity of the evaluation of wall shear stress from the velocity distribution is examined in comparison with the measured result and the calculated one obtained by commercial CFD code. In the focused pulsatile flow case, the variation of wall shear stress distribution is clarified, which is expected to be useful as basic data to understand the major impact of flow field in the arterial Y-shape bifurcation.

Noninvasive Evaluation of Wall Shear Stress on Retinal Microcirculation in Humans

To evaluate wall shear stress (WSS) on retinal microcirculation noninvasively. Retinal vessel diameter (D) and mean centerline blood velocity (V(max, mean)) were measured in the retinal arterioles and venules at first- and second-order branches in 13 subjects using laser Doppler velocimetry (LDV). Retinal blood flow (RBF) and wall shear rate (WSR) were calculated using these two parameters. Blood viscosity at the calculated shear rate was also measured using a cone-plate viscometer. WSS was calculated as the product of the WSR and the blood viscosity. In the first-order branches, the averaged D, V(max, mean), RBF, and WSR(mean) were 108 +/- 13 microm, 41 +/- 10 mm/s, 11 +/- 4 microL/min, and 1539 +/- 383 s(-1) in the arterioles and 147 +/- 13 microm, 23 +/- 3 mm/s, 12 +/- 4 microL/min, and 632 +/- 73 s(-1) in the venules, respectively. The apparent blood viscosities at the measured shear rates were 3.5 +/- 0.3 centipoise (cP) in the arterioles and 3.8 +/- 0.4 cP in the venules. Therefore, the averaged WSS was 54 +/- 13 dyne/cm2 in the arterioles and 24 +/- 4 dyne/cm2 in the venules. The WSS in the second-order arterioles was significantly lower than that in the first-order branches (P = 0.002), but the WSS in the first-order venules was similar to that in the second-order venules. The authors demonstrated that the WSS in the retinal vessels could be evaluated noninvasively in humans using LDV and cone-plate viscometry. This system may be useful for further clinical investigation of the role of shear stress in the pathogenesis of various retinal disorders.

In vitro measurement of fluid-induced wall shear stress in unruptured cerebral aneurysms harboring blebs.

Little attention has been focused on the role of fluid-induced wall shear stress in fully developed cerebral aneurysms. The purpose of this study is to evaluate the alternation and distribution of wall shear stress over 1 cardiac cycle in patients' aneurysms. A middle cerebral artery aneurysm and a basilar tip aneurysm with localized outpouching (blebs) in their domes were selected for this study. With the use of a stereo lithography machine, geometrically realistic aneurysm models were created on the basis of 3-dimensional CT angiograms. In vitro shearing velocity measurement was conducted with the use of laser-Doppler velocimetry at multiple points on the aneurysmal wall to calculate the value of wall shear stress. The wall shear stress was documented at multiple points in the aneurysm inflow zone, dome, and outflow zone. Distribution of wall shear stress was not uniform in the aneurysm walls, and particular regions were exposed to relatively high wall shear stress. The wall shear stress changed dynamically throughout 1 cardiac cycle at the point where a high value of wall shear stress was noted. The blebs of both aneurysms were exposed to high wall shear stress. Unlike previous reports in which an ideal spherical aneurysm model was used, the aneurysm inflow zone was not exposed to high shear stress. In vitro aneurysm models based on the patients' angiograms allowed us to conduct a more realistic evaluation of wall shear stress in the aneurysms harboring blebs. These results provide us with further indications of the correlation of wall shear stress with the natural history of cerebral aneurysms.