Minimum Wall Shear Stress Research Articles

Effects of Suture Position on Left Ventricular Fluid Mechanics under Mitral Valve Edge-to-Edge Repair

Mitral valve (MV) edge-to-edge repair (ETER) is a surgical procedure for the correction of mitral valve regurgitation by suturing the free edge of the leaflets. The leaflets are often sutured at three different positions: central, lateral and commissural portions. To study the effects of position of suture on left ventricular (LV) fluid mechanics under mitral valve ETER, a parametric model of MV-LV system during diastole was developed. The distribution and development of vortex and atrio-ventricular pressure under different suture position were investigated. Results show that the MV sutured at central and lateral in ETER creates two vortex rings around two jets, compared with single vortex ring around one jet of the MV sutured at commissure. Smaller total orifices lead to a higher pressure difference across the atrio-ventricular leaflets in diastole. The central suture generates smaller wall shear stresses than the lateral suture, while the commissural suture generated the minimum wall shear stresses in ETER.

Pressure distribution and wall shear stress in stenosis and abdominal aortic aneurysm by computational fluid dynamics modeling (CFD)

sThe models of stenosed blood vessel with three different types of stenosis types have been modeled to investigate blood flow characteristics. The study was performed to investigate various hemodynamics, such as pressure and wall shear stress (WSS), with the change of stenosis ratio and Reynolds numbers (Re). The results of modeling, the minimum WSS occurred in different regions according to the stenosis types. The change of the diameter of blood vessel showed up in the pre-stenotic region by elastic behavior characteristics of blood vessels. Also, when the thickness of wall of blood vessel is 2 mm, the radius of blood vessel is increased by approximately two-times. As atherosclerosis progresses, the wall of blood vessels gradually loses elasticity and then the thickness of blood vessels gets thinner.

뇌동맥류 모델에 대한 혈류역학 해석

뇌동맥류모델은 CT 영상을 기반으로 추출하여, ANSYS-FLUENT 를 사용해 전산 유체유동해석을 수행하였다. 본 연구를 통해 뇌동맥류에서 최소 벽전단응력은 동맥류가 발생한 영역에서 일어나는 것을 알 수 있다. 또한 뇌동맥류 모델에서 우측중뇌동맥 안쪽벽면에 작용하는 벽전단응력의 크기는 동맥류 전부와 후부의 벽면에 작용하는 벽전단응력의 크기에 비해 20 배 더 크게 발생하는 것을 알 수 있다. 그러나 동맥류 영역에서의 전단응력의 크기는 매우 작게 나타났다. 혈관 수축이 일어나는 동안 동맥류의 영역에서 매우 복잡한 이차유동이 발생하는 것을 볼 수 있다. 동맥류 내부에서의 혈류유동은 나선형 유동형태를 보이며, 본 연구의 혈류역학적 특성 분석을 통해 뇌동맥류의 파열을 예견할 수 있을 것으로 판단한다.

Wall shear stress association with rupture status in volume matched sidewall aneurysms

ObjectiveFlow induced tangential wall shear stress (WSS) is thought to be involved in aneurysm formation, growth, and rupture. Low WSS was previously associated with rupture, but definitive quantitative analyses remain...

Time-Averaged and Fluctuated Wall Shear Stresses Downstream from an Orifice in a Circular Pipe

In the present study, the distributions of time-averaged and fluctuated wall shear stresses downstream from an orifice were measured using a Flow Vector Sensor of MEMS (Micro Electro Mechanical System). The air flow was supplied to a circular pipe from a blow-down wind tunnel. The diameter of the pipe is D = 194 mm and the diameter of the orifice is d = 97mm, yielding a diameter ratio of 0.5. The axial distance from separation (orifice) to reattachment was approximately 2.5D. Near the wall in the recirculating region, the minimum mean wall shear stress was located at approximately x/D = 1.75, and the maximum rms value of the wall shear stress was approximately x/D = 1 - 2. The experimental results were found to approximately agree with the numerical results obtained previously by Large-eddy simulation. It seems that using the fluctuated wall shear stress to estimate the FAC(Flow-Accelerated Corrosion) rate of the circular pipe wall downstream from the orifice is appropriate.

Unsteady blood flow and mass transfer of a human left coronary artery bifurcation: FSI vs. CFD

In this study, a Fluid Solid Interaction analysis (FSI) of a computerized tomography (CT) scan reconstructed left coronary artery was performed. The arterial wall was modeled as an isotropic hyperelastic material. The arterial wall shear stress (WSS) was computed in order to investigate a correlation between flow-induced wall shear stress and geometry of the artery. An unsteady state FSI analysis with a commercial finite element software was performed in order to evaluate the maximum and the minimum wall shear stress as a function of the flow regime and the arterial wall compliance in the left coronary. As boundary conditions, physiological pressure waveforms were applied. Comparison of the computational results between the FSI and rigid-wall models showed that the wall shear stress (WSS) distributions were substantially affected by the arterial wall compliance. In particular, the minimum and maximum WSS values significantly vary.

Hemodynamic Differences Between Unruptured and Ruptured Intracranial Aneurysms During Observation

We evaluated several hemodynamic parameters for the prediction of rupture in a data set of initially unruptured aneurysms, including aneurysms that ruptured during follow-up observation. Aneurysm geometry was extracted from CT angiographic images and analyzed using a mathematical formula for fluid flow under pulsatile blood flow conditions. Fifty side-wall internal carotid posterior communicating artery aneurysms and 50 middle cerebral artery bifurcation aneurysms of medium size were investigated for energy loss, pressure loss coefficient, wall shear stress, and oscillatory shear index. During follow-up observation, 6 internal carotid posterior communicating artery and 7 middle cerebral artery aneurysms ruptured (44 and 43 remained unruptured, respectively, with the same location and a similar size as the ruptured cases). A significant difference in the minimum wall shear stress between aneurysms that ruptured and those that remained unruptured was noted only in internal carotid artery aneurysms (P<0.001). Energy loss showed a higher tendency in ruptured aneurysms but statistically not significant. For pressure loss coefficient, a significant difference was noted in both internal carotid artery (P=0.0046) and middle cerebral artery (P<0.001) aneurysms. Pressure loss coefficient may be a potential parameter to predict future rupture of unruptured aneurysms.

Abstract 2731: CFD Reveals Hemodynamic Differences Between Unruptured And Ruptured Intracranial Aneurysms During Observation

Background and Purpose: Although various studies have been performed, the mechanism leading to the rupture of cerebral aneurysms has not yet been elucidated. Accurate assessment of cerebral aneurysm rupture risk is important because current treatments carry a small but significant risk that can exceed the small natural risk of rupture. Various hemodynamic parameters have been proposed for estimating the risk of rupture of cerebral aneurysms, with limited success. We evaluated several hemodynamic parameters to predict rupture in a dataset of initially unruptured aneurysms in which some aneurysms ruptured during follow-up observation. Methods: Geometry of the aneurysm and blood vessels was extracted from CTA images and analyzed using a mathematical formula for fluid flow under pulsatile blood flow conditions. Fifty side-wall internal carotid posterior communicating artery (ICA-pcom) aneurysms and fifty middle cerebral artery (MCA) bifurcation aneurysms of medium size were investigated for Energy loss (EL), Pressure Loss Coefficient (PLC), wall-shear-stress (WSS) and oscillatory shear index (OSI). During a follow-up observation period, 6 ICA-pcom and 7 MCA aneurysms ruptured (44 and 43 remained unruptured, respectively, with the same location and a similar size as the ruptured cases). Results: A significant difference in the minimum WSS between aneurysms that ruptured and those that remained unruptured was noted only in ICA aneurysms (P&lt;0.001). EL showed higher tendency in ruptured aneurysms but statistically not significant. For PLC, a significant difference was noted in both ICA (P&lt;0.001) and MCA (P&lt;0.001) aneurysms. All other parameters did not show significant differences between the two groups. Conclusion: A significant difference was noted in WSSMIN only in ICA aneurysms. For PLC, a significant difference was noted in both ICA and MCA aneurysms, suggesting that PLC may be one, out of possibly other useful parameters to predict cerebral aneurysm rupture.

D225 円管内オリフィス下流域における壁面せん断応力の時間平均と変動成分(OS6 保全・設備診断技術)

In the present study, the distributions of time-averaged and fluctuated wall shear stresses downstream from an orifice were measured using a Flow Vector Sensor of MEMS (Micro Electro Mechanical System). The air flow was supplied to a circular pipe from a blow-down wind tunnel. The diameter of the pipe is D = 194 mm and the diameter of the orifice is d = 97mm, yielding a diameter ratio of 0.5. The axial distance from separation (orifice) to reattachment was approximately 2.5D. Near the wall in the recirculating region, the minimum mean wall shear stress was located at approximately x/D = 1.5, and the maximum rms value of the wall shear stress was approximately x/D = 1.0-1.75. The experimental results were found to approximately agree with the numerical results obtained previously by Large-eddy simulation. It seems that using the fluctuated wall shear stress to estimate the FAC rate of the circular pipe wall downstream from the orifice is appropriate.

Hemodynamic Simulation of Intra-stent Blood Flow

The stent has been a major breakthrough for the treatment of atherosclerotic vascular disease. The permanent vascular implant of a stent, however, changes the blood flow hemodynamics and may consequently affect the restenosis process. Computational Fluid Dynamics (CFD) has been widely used to analyze the hemodynamic behavior and wall shear stress (WSS) distribution in stented arteries. The objective of this study is to present a thorough comparison among various CFD models to investigate the effects of rheological properties and pulsatile flow on hemodynamic simulation of the intra-stent blood flow. Several CFD models were developed with various modeling setups – axisymmetric parallel ring vs. 3-D stented artery model, Newtonian vs. non-Newtonian flow, and steady-state vs. pulsatile flow. Simulated results show that the minimum WSS occurs at the recirculation zones located at the downstream or backside of each stent struts. The rheological effect on WWS is minor in the axisymmetric parallel ring model; however, it becomes slightly significant in the 3-D stented artery model, with Newtonian flow being a more conservative assumption. For given pulsatile waveforms, the steady-state and pulsatile flow resulted in fairly similar trends in the WSS distribution. Therefore, it is reasonable to simulate the intra-stent blood flow as a steady-state Newtonian flow, which could be beneficial in more complex simulations and drastically reduce the computational time. These findings will provide great insights for future stent design optimization to reduce restenosis.

Possibility of atherosclerosis in an arterial bifurcation model.

Arterial bifurcations are susceptible locations for formation of atherosclerotic plaques. In the present study, steady blood flow is investigated in a bifurcation model with a non-planar branch. The influence of different bifurcation angles and non-planar branch is demonstrated on wall shear stress (WSS) distribution using three-dimensional Navier-Stokes equations. The WSS values are low in two locations at the top and bottom walls of the mother vessels just before the bifurcation, especially for higher bifurcation angles. These regions approach the apex of bifurcation with decreasing the bifurcation angle. The WSS magnitudes approach near to zero at the outer side of bifurcation plane and these locations are separation-prone. By increasing the bifurcation angle, the minimum WSS decreases at the outer side of bifurcation plane but low WSS region squeezes. WSS peaks exist on the inner side of bifurcation plane near the entry section of daughter vessels and these initial peaks drop as bifurcation angle is increased. It is concluded that the non-planarity of the daughter vessel lowers the minimum WSS at the outer side of bifurcation and increases the maximum WSS at the inner side. So it seems that the formation of atherosclerotic plaques at bifurcation region in direction of non-planar daughter vessel is more risky.

Spatial and temporal resolution of shear in an orbiting petri dish

It is well documented that physiological and morphological properties of anchored cells are influenced by fluid shear stress. Common orbital shakers provide a means of simultaneously applying shear stress to cells for tens to hundreds of cases by loading the shaker with multiple dishes. However, the complex flow in orbiting dishes is amenable to analytical solution for resolving shear created by the fluid motion only for simplified conditions. The only existing quantification of shear in this flow is an equation that estimates a constant scalar value of shear for the entire surface of the dish. In practice, wall shear stress (WSS) will be oscillatory rather than steady due to the travelling waveform and will vary across the surface of the dish at any instant in time. This article presents a computational model that provides complete spatial and temporal resolution of WSS over the bottom surface of a dish throughout the orbital cycle. The model is reasonably well validated by the analytical solution, with resultant WSS magnitudes that are within 0.99 ± 0.42 dyne/cm(2) . The model results were compared to tangential WSS magnitudes obtained using one-dimensional optical velocimetry at discreet locations on the bottom of an orbiting dish. The experimental minimum and maximum WSS at 1 mm from the center of the dish were 6 and 7 dyne/cm(2) , respectively, whereas WSS generated from the computational model ranged from 0.5 to 8.5 dyne/cm(2) . The experimental minimum and maximum WSS at 12 mm from the center of the dish were 6 and 16 dyne/cm(2) , respectively, whereas WSS generated from the computational model ranged from 0.5 to 14 dyne/cm(2) . Discrepancies between the experimental and computational data may be attributed to a sparse sampling rate for the experimental probe, a sharp gradient at the sample area which could cause the unidirectional probe to be inaccurate if its location were not precise, and too few particles to track and a scattering of the signal by the free surface when the liquid is shallow.

Heat transfer and flow through a super-elliptic duct – Effect of corner rounding

Properties of fully developed viscous flow through a super-elliptic duct are reported. The cross section resembles rectangular ducts with rounded corners. The effect of corner rounding depends on the aspect ratio, and in general decreases both flow and convective (H1) heat transfer but increases minimum wall shear stress. An accurate, efficient Ritz method is used.

협착 동맥에서의 맥동 혈류 유동에 대한 수치해석적 연구

In the present computational study, simple stenotic artery models using pulsatile flow condition were investigated. A 1 Hz non-reversing sinusoidal velocity for pulsatile flow was imposed at the flow inlet and the corresponding Womersley number based on the vessel radius is 2.75. The simple stenotic geometries have been used that consist of 25%, 50% and 75% semicircular constriction in a cylindrical tube. In this paper, numerical solutions are presented for a first harmonic oscillatory flow using commercial software ADINA 8.4. As stenosis and Reynolds number increase, the maximum wall shear stress(WSS) increases while the minimum WSS decreases. As the stenotic rate increases, the pressure drop at the throat severely decreases to collapse the artery and plaque. It is found that the fluid mechanical disturbances due to the constriction were highly sensitive with rate of stenosis and Reynolds number. When Reynolds number and stenosis increase, the larger recirculation region exists. In this recirculation region the possibility of plaque attachment is increasingly higher. The present results enhance our understanding of the hemodynamics of a stenotic artery.

Fluid–structure interaction modeling of blood flow and cerebral aneurysm: Significance of artery and aneurysm shapes

Because wall shear stress (WSS) is known to play an important role in initiation, growth and rupture of cerebral aneurysm, predicting the hemodynamic forces near the aneurysmal site helps with understanding aneurysms better. Earlier research reports indicate that the WSS around the aneurysmal site has a significant relationship with the vascular and aneurysm morphology. It was also shown statistically that the aneurysm shape (aspect ratio) is an indicator of rupture risk in cerebral aneurysm. In this study, fluid–structure interaction (FSI) modeling of a ruptured aneurysm, two unruptured aneurysms at the middle cerebral artery (MCA) bifurcation, and a MCA bifurcation without aneurysm is carried out using vascular geometries reconstructed from CT images. We use pulsatile boundary conditions based on a physiological flow velocity waveform and investigate the relationship between the hemodynamic forces and vascular morphology for different arteries and aneurysms. The results are compared with the results obtained for the rigid arterial wall to highlight the role of FSI in the patient-specific modeling of cerebral aneurysm. The results show that the interaction between the blood flow and arterial deformation alters the hemodynamic forces acting on the arterial wall and the interaction strongly depends on the individual aneurysm shapes. Flow impingement on the arterial wall plays a key role in determining the interaction and hemodynamic forces. When the blood flow impinges strongly on the wall, the maximum WSS tends to decrease due to the flow–wall interaction. When the blood flows straight into an aneurysm, the flow and the resulting WSS patterns are altered both qualitatively and quantitatively. When the blood in the aneurysm is nearly stagnant, a slow flow is induced by the wall motion, which raises the minimum WSS on the aneurysmal wall. The results reinforce the importance of FSI in patient-specific analysis of cerebral aneurysms.

Measurement of systolic and diastolic arterial wall shear stress in the ascending aorta

Purpose Wall shear stress (WSS) appears to contribute significantly in the initiation and progression of atherosclerotic disease. The purpose of this work is to present in vivo systolic and diastolic WSS calculations in the human ascending aorta by the application of three straightforward methodologies based on Poiseuille's theory of flow. Materials and methods Blood flow measurements were performed retrospectively in the ascending aorta of 20 non-atherosclerotic patients using phase-contrast MRI. WSS calculations were performed assuming Poiseuille's theory of flow based on average flow volume, average flow velocity and maximum flow velocity. Systolic and diastolic WSS values were calculated and compared with the calculated maximum and minimum values of WSS throughout the cardiac cycle. Results Systolic WSS values calculated by average flow volume, average flow velocity and maximum flow velocity were similar (0.4 ± 0.2 N/m 2, 0.4 ± 0.3 N/m 2and 0.4 ± 0.2 N/m 2, respectively). Diastolic WSS values calculated by maximum flow velocity were significantly higher (11.6 ± 7.0 × 10 −2 N/m 2) compared to values calculated by average flow volume (0.3 ± 0.9 × 10 −2 N/m 2) and average flow velocity (0.3 ± 1.0 × 10 −2 N/m 2). Comparison of systolic and diastolic WSS values with maximum and minimum WSS values showed that time instances of maximum and minimum blood flow velocities do not coincide with time instances of maximum and minimum blood flow volume. Conclusion In vivo calculation of WSS in the ascending aorta is feasible by phase-contrast MRI flow measurements and straightforward methodologies based on Poiseuille's theory of flow. However, measurements based on maximum flow velocity show larger deviations compared to measurements based on mean flow volume or mean flow velocity.

Study for Flow Structure within Real Aneurysm Induced in Anterior Communicating Artery

The mechanism involved in the formation and subsequent rupture of cerebral aneurysm has not been clarified adequately. The aneurysm frequently appears at the flow divider where the flow bifurcates to the anterior communicating artery and the anterior cerebral artery. In the present study, the flow pattern and the wall shear stress (WSS) within the real aneurysm model having bleb are measured using PIV. On the basis of the MRI data of human cerebral artery with aneurysm, the aneurysm model is reconstructed by the optical 3D design with CAD. WSS abruptly changes along the aneurysmal wall and minimum WSS appears at bottom wall of the bleb. Particularly, WSS is small along the bleb wall. It would be associated with the degeneration of bleb wall such as the formation of thrombosis.

Influence of ionic strength on complex formation between poly(ethylene oxide) and cationic surfactant and turbulent wall shear stress in aqueous solution

Abstract We investigate the influence of ionic strength on the interaction between poly(ethylene oxide) (PEO) and cationic surfactant, hexadecyltrimethylammonium chloride (HTAC), and the consequent effect on turbulent drag reduction in aqueous PEO/HTAC solutions. Conductivity and surface tension data for PEO-HTAC in aqueous solution indicate that salt stabilizes binding of HTAC micelles to the polymer. Dynamic light scattering analysis indicates an increase in hydrodynamic radius for HTAC micelles in aqueous salt solution. In contrast, salt reduces the hydrodynamic radius of PEO-HTAC complexes. The latter observation is consistent with contraction of the PEO-HTAC complex via electrostatic screening. For the measurement of turbulent drag reduction in a Couette cell, our data indicate that the minimum wall shear stress in aqueous HTAC solutions occurs at an optimum HTAC concentration, close to CMC, and this optimum concentration value decreases with increasing ionic strength. This result suggests a lowering of the CMC in turbulent flow. For aqueous PEO-HTAC mixtures, the minimum wall shear stress occurs at an optimum PEO concentration smaller than that of pure PEO solutions, and this optimum concentration value increases with ionic strength. Our findings provide evidences that the turbulent wall shear stress does not always scale inversely with the hydrodynamic volume of the polymer–surfactant complex.

Computational analysis of effects of external carotid artery flow and occlusion on adverse carotid bifurcation hemodynamics.

This is a computational analysis of the effects of external carotid artery (ECA) flow, waveform, and occlusion geometry on two hemodynamic wall parameters associated with intimal hyperplasia and atherosclerosis. Study design Transient three-dimensional fluid mechanics analysis was applied to a standard carotid artery bifurcation. Mean internal carotid artery (ICA) flow was maintained at 236 mL/min with a normal waveform. ECA flow was increased from zero to 151 mL/min (64% of ICA flow) with both a normal biphasic waveform and a damped waveform. Geometry of five ECA occlusions was studied: distal, proximal stump, smooth, smooth without carotid sinus, and optimal reconstruction.Primary outcome measures Two time-averaged and area-averaged hemodynamic wall parameters were computed from the velocity and wall shear stress (WSS) solutions, ie, wall shear stress angle gradient (WSSAG) and oscillatory shear index (OSI). Both local and area-averaged hemodynamic wall parameters were computed for the distal common carotid artery (CCA) and the proximal ICA. When ECA flow with a normal waveform is increased from zero to 151 mL/min, area-averaged WSS values increase in the CCA, from 3.0 to 4.4 dynes/cm(2) (46%), and in the ICA, from 16.5 to 17.1 dynes/cm(2) (4%); minimum local WSS values in the carotid sinus remain less than 1 dyne/cm(2); maximum local values of WSSAG and OSI are observed in the carotid sinus and increase from 3.5 to 9.1 radian/cm (160%) and 0.23 to 0.46 (100%), respectively; CCA plus ICA area-averaged WSSAG increases by 52%, and OSI increases by 144%; and damping of the ECA waveform has little effect on local or area-averaged WSSAG but reduces OSI to 68%. When the ECA is occluded, the minimum local WSS in the carotid sinus is less than 1 dyne/cm(2). However, if the carotid sinus is removed or the CCA-ICA geometry hemodynamically optimized, the minimum WSS is approximately 4 dynes/cm(2). Similarly, eliminating the carotid sinus markedly reduces local maximum WSSAG, from 3.0-3.5 radian/cm to 0.3 radian/cm, and reduces local maximum OSI from 0.22-0.49 to 0.04. Area-averaged WSSAG and OSI over the CCA and ICA are reduced by approximately 50% with elimination of the carotid sinus. The degree of adverse carotid bifurcation hemodynamics as measured with WSSAG and OSI is directly proportional to ECA flow. The marked difference in normal ICA and ECA flow waveforms does not contribute to adverse wall hemodynamics. Location of an ECA occlusion (distal, proximal, stump, smooth) does not affect adverse carotid hemodynamics; however, marked improvement is obtained with elimination of the carotid sinus.

In vivo wall shear stress measured by magnetic resonance velocity mapping in the normal human abdominal aorta

To apply a new non-invasive method for quantification of in vivo wall shear stress (WSS) by magnetic resonance (MR) FAcE velocity mapping and measure WSS in the human abdominal aorta. Prospective, open study. Six volunteers. MR FAcE velocity method was developed for measurements of mean, maximum, minimum WSS and oscillating shear index (OSI) values at the anterior and posterior walls of suprarenal and infrarenal abdominal aorta. The mean, maximum and minimum WSS values were 0.63/0.28, 4.07/2.72 and -0.71/-1.00 N/m2, respectively, in the suprarenal/infrarenal aorta. The mean WSS was 0.35 N/m2 (p < 0.001) and the maximum WSS was 1.36 N/m2 (p < 0.0001) lower in the infrarenal aorta than in the suprarenal aorta. Mean, maximum minimum WSS and OSI values in the infrarenal position differed (p < 0.01) between the anterior and posterior walls. WSS can be determined in vivo by MR FAcE velocity technique. Since the lowest WSS values were measured in the infrarenal, posterior blood-to-wall interface, the theory of more pronounced atherosclerosis development in low and oscillating WSS domains was not contradicted by the results of the present study.