Wall shear stress (WSS) has been associated with atherogenesis and plaque progression. The present study assessed the value of WSS analysis derived from conventional coronary angiography to detect ...lesions culprit for future myocardial infarction (MI).
Three-dimensional quantitative coronary angiography (3DQCA), was used to calculate WSS and pressure drop in 80 patients. WSS descriptors were compared between 80 lesions culprit of future MI and 108 non-culprit lesions (controls). Endothelium-blood flow interaction was assessed by computational fluid dynamics (10.8 ± 1.41 min per vessel). Median time between baseline angiography and MI was 25.9 (21.9–29.8) months. Mean patient age was 70.3 ± 12.7. Clinical presentation was STEMI in 35% and NSTEMI in 65%. Culprit lesions showed higher percent area stenosis (%AS), translesional vFFR difference (ΔvFFR), time-averaged WSS (TAWSS) and topological shear variation index (TSVI) compared to non-culprit lesions (p < 0.05 for all). TSVI was superior to TAWSS in predicting MI (AUC-TSVI = 0.77, 95%CI 0.71–0.84 vs. AUC-TAWSS = 0.61, 95%CI 0.53–0.69, p < 0.001). The addition of TSVI increased predictive and reclassification abilities compared to a model based on %AS and ΔvFFR (NRI = 1.04, p < 0.001, IDI = 0.22, p < 0.001).
A 3DQCA-based WSS analysis was feasible and can identify lesions culprit for future MI. The combination of area stenoses, pressure gradients and WSS predicted the occurrence of MI. TSVI, a novel WSS descriptor, showed strong predictive capacity to detect lesions prone to cause MI.
Display omitted
•Lesions culprit of future myocardial infarction (MI) had higher area stenosis, pressure gradient, time-averaged wall shear stress (TAWSS) and topological shear variation index (TSVI).•A three-dimensional quantitative coronary angiography (3DQCA)-based software provided in few minutes reliable WSS simulations.•The WSS topological skeleton feature TSVI showed strong predictive capacity for MI.
•A conductivity probe design allows detailed measurements in the near-wall zone.•The electrodiffusion method was adapted to measure shear stress in a rod assembly.•The spacer grid changes the void ...fraction distribution from saddle to dome-shaped.•Such redistribution leads to non-monotonic change in wall shear stress along flow.
This study focuses on the experimental investigation of local characteristics of upward bubble flow in a 3 × 3 square rod bundle assembly. The experiments were conducted at Reynolds numbers ranging from 4000 to 11000 and gas void fractions up to 10%. The distribution of the gas phase around the central rod of the assembly was measured using a frontal conductivity probe, while the wall shear stress on the central rod was obtained through the electrodiffusion method. It is shown that the gas phase distribution does not exhibit the symmetry characteristic of the assembly cross-section. Furthermore, as the distance from the spacer grid increases, a reconfiguration of void fraction profiles is observed. This explains the non-monotonic dependence of wall shear stress and wall shear stress fluctuations on the distance to the spacer grid.
Carotid plaque vulnerability is a significant factor in the risk of cardiocerebrovascular events, with intraplaque neovascularization (IPN) being a crucial characteristic of plaque vulnerability. ...This study investigates the value of ultrasound vector flow imaging (V-flow) for measuring carotid plaque wall shear stress (WSS) in predicting the extent of IPN.
We enrolled 140 patients into three groups: 53 in the plaque group (72 plaques), 23 in the stenosis group (27 plaques), and 64 in the control group. V-flow was used to measure WSS parameters, including the average WSS (WSS mean) and the maximum WSS (WSS max), across three plaque locations: mid-upstream, maximum thickness, and mid-downstream. Contrast-enhanced ultrasound examination was used in 76 patients to analyze IPN and its correlation with WSS parameters.
WSS max in the stenosis group was significantly higher than that in the control and plaque groups at the maximum thickness part (P < .05) and WSS mean in the stenosis group was significantly lower than that in the control group at the mid-upstream and mid-downstream segments (P < .05). WSS mean in the plaque group was significantly lower than that of the control group at all three locations (P < .05). Contrast-enhanced ultrasound examination revealed that plaques with neovascularization enhancement exhibited significantly higher WSS values (P < .05), with a positive correlation between WSS parameters and IPN enhancement grades, particularly WSS max at the thickest part (r = 0.508). Receiver operating characteristic curve analysis of WSS parameters for evaluating IPN showed that the efficacy of WSS max in evaluating IPN was better than that of WSS mean (P < .05), with an area under the curve of 0.7762 and 0.6973 (95% confidence intervals, 0.725-0.822 and 0.642-0.749, respectively). The cut-offs were 4.57 Pa and 1.12 Pa, sensitivities were 74.03% and 63.64%, and specificities were 75.00% and 68.18%.
V-flow effectively measures WSS in carotid plaques. WSS max provides a promising metric for assessing IPN, offering potential insights into plaque characteristics and showing some potential in predicting plaque vulnerability.
Protein adsorption first occurs for the blood-contacting bio-metallic stents, which plays essential roles in the biofilm formation and subsequent flow-induced corrosion. The synergistic effects of ...bovine serum albumin (BSA) and wall shear stress (WSS) on the corrosion of WE43 magnesium (Mg) alloy have been studied. The results indicate that BSA and WSS play competitive roles in accelerating the corrosion, specifically dominate under low WSS and a higher WSS respectively. Machine learning (ML) method is utilized to model the intrinsic corrosion mechanism. We expect this study might offer novel perspectives for better evaluating in vitro corrosion of Mg-based stents.
•Synergistic effects of protein and shear stress on corrosion behaviors of WE43 alloy are studied.•The BSA adsorption evolutions under the simulated physiological flow field are clarified.•The adsorbed BSA accelerates the static corrosion by inhibiting the Ca-P deposition.•The corrosion mechanisms are dominated by different influencing factors under various WSS values.•The interactive relationships between BSA and WSS on corrosion are predicted by machine learning.
The effects of flow velocity and silty sand on CO2 corrosion of N80 carbon steel were studied using a small flow loop. Silty sand does not change the electrochemical characterization of corrosion but ...reduces the corrosion rate of steel. Under the low flow velocity, silty sand embeds in the sample surface, reducing active area for iron dissolution and delaying the formation of FeCO3 in corrosion product layer. At medium and high flow velocity, silty sand erodes the sample surface, and wall shear stress damages the integrity of the corrosion product layer, but do not lead to greater corrosion rate.
•Flow corrosion tests and in-situ electrochemical measurements were carried out using a small flow loop.•The corrosion rate of N80 steel increases with increasing flow velocity, and the critical flow velocity for N80 steel is between 1.5 m/s and 3.0 m/s.•Silty sand does not change the electrochemical characterization of steel corrosion but reduces the corrosion rate.•Silty sand embeds in the sample surface and reduces the active area for iron dissolution at low flow velocity. As the flow velocity increases, silty sand erodes the sample surface and damages the integrity of corrosion product layer.
Fluid flow dynamics within porous scaffolds for tissue engineering play a critical role in the transport of fundamental materials to the cells and in controlling the biocompatibility of the scaffold. ...Properties such as permeability and fluid flow-induced wall shear stress characterize the biological behavior of the scaffolds. Bioactivity depends on the diffusion of oxygen and other nutritious elements through the porous medium and fluid flow-induced shear stress is known as the dominant mechanical stimulant of cell differentiation and proliferation within the scaffolds. In this study, eight different bone scaffold models with a constant porosity of 80% were designed computationally using the TPMS and lattice-based structures. We investigated the fluid flow within the scaffolds using CFD analysis. The results of the work showed that scaffold architecture has a significant impact on the permeability and that scaffold permeability can vary up to three times depending on the architecture. The scaffolds with the minimal variation in their channel size exhibited the highest permeability. We investigated the distribution statistics of wall shear stress on the walls of the scaffolds and showed that a correlation between the architecture of the scaffolds and the distribution statistics of wall shear stress did not exist. The outcomings of this work can be promising in designing better scaffolds in tissue engineering from a biological point of view.
•Minimal surface and lattice-based architectures exhibit different flow behavior.•Scaffold permeability can vary up to three times depending on the architecture.•Scaffolds with minimal variation in channel size exhibit the highest permeability.•Wall shear stress distribution does not correlate with scaffold architecture.•Scaffold design with desired wall shear stress distribution is problematical.
The non-uniform distribution of atherosclerosis within the arterial system has been attributed to pro-atherogenic influences of low, oscillatory haemodynamic wall shear stress (WSS) on endothelial ...cells (EC). This theory is challenged by the changes in lesion location that occur with age in human and rabbit aortas. Furthermore, a number of point-wise comparisons of lesion prevalence and WSS have failed to support it. Here we investigate the hypothesis that multidirectional flow—characterized as the average magnitude of WSS components acting transversely to the mean vector (transWSS)—plays a key role. Maps of lesion prevalence around aortic branch ostia in immature and mature rabbits were compared with equivalent maps of time average WSS, the OSI (an index characterizing oscillatory flow) and transWSS, obtained from computational simulations; Spearman’s rank correlation coefficients were calculated for aggregated data and 95% confidence intervals were obtained by bootstrapping methods. Lesion prevalence correlated positively, strongly and significantly with transWSS at both ages. Correlations of lesion prevalence with the other shear metrics were not significant or were significantly lower than those obtained for transWSS. No correlation supported the low, oscillatory WSS theory. The data are consistent with the view that multidirectional near-wall flow is highly pro-atherogenic. Effects of multidirectional flow on EC, and methods for investigating them, are reviewed. The finding that oscillatory flow has pro-inflammatory effects when acting perpendicularly to the long axis of EC but anti-inflammatory effects when acting parallel to it may explain the stronger correlation of lesion prevalence with transWSS than with the OSI.
When endothelium is cultured in wells swirled on an orbital shaker, cells at the well centre experience putatively atherogenic flow whereas those near the edge experience putatively atheroprotective ...flow. Transcellular transport is decreased equally in both regions, consistent with it being reduced by a mediator released from cells in one part of the well and mixed in the swirling medium. Similar effects have been inferred for pro-inflammatory changes. Here we identify the mediator and flow characteristics stimulating its release.
Medium conditioned by cells swirled at the edge, but not by cells swirled at the centre or cultured under static conditions, significantly reduced transendothelial transport of a low density lipoprotein (LDL)-sized tracer and tumor necrosis factor α (TNF-α)-induced activation and translocation of nuclear factor κB (NF-κB), adhesion molecule expression and monocyte adhesion. Inhibiting transcytosis similarly decreased tracer transport. Unbiased proteomics revealed that cells from the swirled edge secreted substantially more follistatin-like 1 (FSTL1) than cells from the swirled centre or from static wells. Exogenous FSTL1 reduced transport of the LDL-sized tracer and of LDL itself, as well as TNF-α-induced adhesion molecule expression. Bone morphogenetic protein 4 (BMP4) increased transport of the LDL-sized tracer and adhesion molecule expression; FSTL1 abolished these effects.
Putatively atheroprotective flow stimulates secretion of FSTL1 by cultured endothelial cells. FSTL1 reduces transcellular transport of LDL-sized particles and of LDL itself, and inhibits endothelial activation. If this also occurs in vivo, it may account for the atheroprotective nature of such flow.
Display omitted
•Endothelial cells exposed to atheroprotective flow secrete FSTL1.•FSTL1 reduces transendothelial transport of LDL and LDL-sized tracers.•FSTL1 reduces the pro-inflammatory effects of TNF-α.
•Newtonian fluid model underestimates wall shear stress compared to non-Newtonian.•Non-Newtonian fluid models experience reduced disturbed flow compared to Newtonian.•Non-Newtonian fluid predicts ...reduced exposure to low and oscillatory shear stress.•Regions of high oscillatory shear index demarcate regions of flow recirculation.
The development of atherosclerosis at the carotid bifurcation is impacted by local variations in wall shear stress (WSS) magnitude and direction, as well as flow complexity within the vessel. In this study, stereoscopic particle image velocimetry (PIV) was used to investigate multidirectional WSS and disturbed flow for idealized models of the carotid bifurcation with varying eccentric stenosis of the internal carotid artery (ICA) and both Newtonian (N-fluid) and non-Newtonian (nN-fluid) blood analogues. Turbulence intensity (TI) was reduced with the nN-fluid compared to N-fluid for mild to moderate stenosis, and comparable for more severely stenosed (70%) models. Differences in maximum TI due to viscosity model ranged from 0.02 m/s to 0.06 m/s compared to much larger differences due to geometry of up to 0.29 m/s between mild and severe stenosis. The level of time-averaged WSS (TAWSS) increased with stenosis severity from 5 Pa to 32 Pa, and nN-fluid led to higher WSS on average than N-fluid counterparts. Regions of elevated oscillatory shear index (OSI) demarcated recirculation regions, and mean OSI in the ICA branch was reduced for nN-fluid models by 9–19% compared to N-fluid. Transverse WSS (transWSS) increased with WSS magnitude and again was higher in nN-fluid models. Surface area exposure to shear metrics indicated that a Newtonian viscosity assumption predicted larger regions of low and oscillatory WSS, while predicting reduced regions of high transWSS, in comparison to the more physiological shear thinning fluid.
Patient-specific computational fluid dynamics (CFD) is a promising tool that provides highly resolved haemodynamics information. The choice of blood rheology is an assumption in CFD models that has ...been subject to extensive debate. Blood is known to exhibit shear-thinning behaviour, and non-Newtonian modelling has been recommended for aneurysmal flows. Current non-Newtonian models ignore rouleaux formation, which is the key player in blood's shear-thinning behaviour. Experimental data suggest that red blood cell aggregation and rouleaux formation require notable red blood cell residence-time (RT) in a low shear rate regime. This study proposes a novel hybrid Newtonian and non-Newtonian rheology model where the shear-thinning behaviour is activated in high RT regions based on experimental data. Image-based abdominal aortic and cerebral aneurysm models are considered and highly resolved CFD simulations are performed using a minimally dissipative solver. Lagrangian particle tracking is used to define a backward particle RT measure and detect stagnant regions with increased rouleaux formation likelihood. Our novel RT-based non-Newtonian model shows a significant reduction in shear-thinning effects and provides haemodynamic results qualitatively identical and quantitatively close to the Newtonian model. Our results have important implications in patient-specific CFD modelling and suggest that non-Newtonian models should be revisited in large artery flows.
PDF
