Oscillatory Shear Index Research Articles

Effect of exercise rehabilitation on hemodynamic performance after 5 carotid artery stenting: a numerical study

Purpose A high in-stent restenosis rate and thrombosis have compromised clinical benefits after vascular stent placement. Exercise rehabilitation after stenting emerges as a promising and practical therapeutic strategy to improve the clinical performance of this therapy, although it remains controversial. The present study aims to explore the impact of exercise training on hemodynamic performance after vascular stent implantation. Methods Different 3-dimensional computational models based on the patient-specific carotids were constructed to calculate hemodynamic parameters, including flow velocity, time-averaged wall shear (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT). Results The results demonstrated that exercise training increased TAWSS but decreased OSI and RRT in some cases after the intervention, and high-intensity exercise would further suppress the adverse blood flow. However, exercise training would remarkably reduce TAWSS and elevate OSI and RRT in patients with mild stenosis at upstream of stented segment. Additionally, we discovered that the hemodynamic environment change induced by exercise training was not significant compared to the stent position in some cases. Exercise would have a less beneficial impact on the disturbed blood flow after the distal common carotid artery (CCA) stenting. Conclusions These findings highlight that exercise-induced hemodynamic changes differ under different conditions. The exercise training for the intervention patients should only be performed after a comprehensive vascular function assessment.

AT1R blocker prevents mental stress induced retrograde blood flow in overweight/obese men.

The main goal was to determine the impact of mental stress (MS) on blood flow regulation in overweight/obese men. Fourteen overweight/obese men (27 ± 7 years; 29.8 ± 2.6kg/m2 ) participated in two randomized experimental sessions with oral administration of the AT1R blocker Olmesartan (40 mg; AT1RB) or placebo (PL). After 2 h, a 5-min acute MS session (Stroop Color Word Test) was administered. Blood flow was assessed at baseline and during the first 3 min of MS by vascular ultrasound in the brachial artery. Blood was collected before (baseline) and during mental stress (MS) for measurement of nitrite (chemiluminescence) and endothelin-1 (ELISA kit). The AT1R blocker was able to reverse the MS responses observed in the placebo session for retrograde flow (p < 0.01), retrograde SR (p < 0.01) and oscillatory shear index (p=0.01). Regarding vasoactive substances, no differences were observed in ET-1 (p > 0.05) responses to MS between experimental sessions. However, for nitrite responses, the administration of the AT1R blocker was able to increase circulating levels of NO (p=0.03) Blockade of AT1R appears to prevent the decrease in endothelial function by reducing low shear stress and maintaining the vasoactive substances balance after MS in overweight/obese men.

Changes in Internal Thoracic Artery Blood Flow According to the Degree of Stenosis of the Anterior Descending Branch of the Left Coronary Artery.

Computational fluid dynamics has enabled the evaluation of coronary flow reserve. The purpose of this study was to clarify the hemodynamic variation and reserve potential of the left internal thoracic artery (LITA). Four patients were selected on the basis of various native coronary stenosis patterns and graft design. The wall shear stress and oscillatory shear index were measured, and one patient was selected. Next, we created three hypothetical lesions with 75%, 90%, and 99% stenosis in front of the graft anastomosis, and compared the changes in LITA blood flow and coronary flow distribution. In the 75% to 90% stenosis model, blood flow was significantly higher in the native coronary flow proximal to the coronary artery bypass anastomosis regardless of time phase. In the 99% stenosis model, blood flow from the LITA was significantly dominant compared to native coronary flow at the proximal site of anastomosis. The range of LITA flow variability was the largest at 99% stenosis, with a difference of 70 ml/min. The 99% stenosis model showed the highest LITA flow. The range of LITA flow variability is large, suggesting that it may vary according to the rate of native coronary stenosis.

Analysis of Hemodynamic Effect on Different Stent Strut Configuration in Femoral Popliteal Artery during the Physical and Physiological Conditions

Peripheral arterial disease (PAD) is a narrowing of the peripheral arteries that might result in blockage if not immediately treated. Normally, an invasive technique called stenting is used at the stenosed arterial region to restore normal blood flow. Thus, it promotes the formation of thrombosis on the stented artery due to the presenting flow recirculation. However, the rate of thrombosis growth was reported to be different for both genders. This is due to an increase in body surface area, body mass index, and weight of the body. Thus, this study aims to investigate the effect of the physiological and physical conditions of men and women with different hemodynamic parameters on the strut configuration in FPA. Five different stent strut configurations were modelled and inserted into the FPA. The computational fluid dynamic (CFD) method was implemented to solve the continuity and N-S equations. The hemodynamic performance of the stent was analyzed based on hemodynamic parameters consisting of time- averaged wall shear stress (TAWSS), time-averaged wall shear stress gradient (TAWSSG), oscillatory shear index (OSI), and relative residence time (RRT). According to the observations, the distal region of the stented FPA had more dominant flow re-circulation than the proximal region. The high void area contributed to less growth of the thrombosis.

Predicting the Risk of Type B Aortic Dissection Using Hemodynamic Parameters in Aortic Arches: A Comparative Study between Healthy and Repaired Aortas

Background and objectiveThe development of acute aortic dissection (AD) remains unpredictable due to the intricate nature of the AD mechanism and the varied patient-specific aortic anatomy. The aim of this study was to simulate the hemodynamic parameters in the aortas before the onset of TBAD with healthy controls. MethodsThis study numerically assessed the effectiveness of hemodynamic indicators in predicting the risk of type B AD (TBAD) by investigating the differences in hemodynamic parameters between healthy and repaired aortas (aortas before TBAD development). Four wall shear stress (WSS)-based indicators and three helicity-based indicators were adopted and analyzed. ResultsThe results showed that more pathological anatomical feathers can be observed in the repaired aortas. For WSS-based indicators, only averaged cross flow index (CFI) and oscillatory shear index OSI (CFI, 1.03 ± 0.07 vs. 0.83 ± 0.10 and OSI, 0.12 ± 0.03 vs. 0.04 ± 0.02) (all p<0.001) were significantly higher in the repaired aortas than those in the healthy aortas. On the other hand, average helicity in the repaired aortas also showed a significant difference compared with that in healthy aortas (h1, 3.88 ± 5.55 vs. -8.03 ± 14.16) (p<0.05). Furthermore, the skewed helical structure and flow disturbance was found in the repaired aortas. Conclusion1) There are marked differences in pathological anatomical features, such as aortic dilation, elongation and tortuosity between the healthy aortas and repaired aortas, and the corresponding hemodynamic indicators also have also been significantly changed. 2) Compared with anatomical characteristics, hemodynamic indicators may be more accurate for predicting the risk and location of TBAD, such as the OSI and CFI index were significantly enhanced in the region where the entry tears have occurred. 3) In clinical practice, anatomical features remain important factors for assessing the risk for development of TBAD; however, hemodynamic analyses with quantitative data and more visualizing characteristics have showed promising potential in this aspect.

Mechanistic modelling of Virchows triad to assess thrombogenicity and stroke risk in atrial fibrillation patients

Abstract Background Atrial fibrillation (AF) is responsible for almost one third of all strokes, with the left atrial appendage (LAA) being the primary thromboembolic source due to localised stimulation of prothrombotic mechanisms; blood stasis, hypercoagulability and endothelial damage, known as Virchow's triad. Aim We propose an in-silico modelling pipeline that leverages clinical imaging data to mechanistically assess patient thrombogenicity for all aspects of Virchow's triad to improve the prediction and prevention of AF-related stroke. Methods Two AF patients undergoing Cine magnetic resonance imaging (sinus rhythm (SR) N=1 or AF N=1 during imaging) were selected for 3D left atrial (LA) modelling with patient-specific myocardial deformation prescribed from image-derived wall motion. Blood stasis was quantified by computational fluid dynamics (CFD) simulations of 5 cardiac cycles [1]. Generation of three key coagulation proteins; thrombin, fibrinogen and fibrin, were modelled to represent thrombus growth and hypercoagulability [2]. Regions prone to thrombogenesis by endothelial damage were identified by the oscillatory shear index (OSI), time averaged wall shear stress (TAWSS) and endothelial cell activation potential (ECAP) metrics in the LAA [3]. Results Patient-specific LA simulations enabled the assessment of differences between SR and AF conditions, quantified as numerical characteristics of each aspect of Virchow's triad. In SR, blood flow velocities were in the range 0–2.6 m/s with mean of 0.85 m/s in the LA cavity, while AF had a range between 0–1.6 m/s with mean of 0.55 m/s. The peak and mean LAA velocities in SR were 0.85 m/s and 0.14 m/s, while AF had a peak LAA velocity of 0.32 m/s and mean of 0.09 m/s, showing a 38% decrease during AF. The thrombin concentration reached its steady state at 1.26 mmol/m3 in the AF case after 4.7 seconds, while thrombin was washed away from the initial injury site in SR. After 5 cardiac cycles of thrombus growth dynamics, the peak fibrin concentration in the LAA was 1.3 mmol/m3 in SR and 3.8 mmol/m3 in AF, with the thrombus area in AF being 40% larger. Fibrinogen concentration decreased at a rate equal to fibrin generation in both SR and AF solely in the area of thrombus formation. ECAP in the LAA had peak values of 2.9 in SR and 3.7 in AF, with the location at highest risk of thrombogenesis above the LAA entrance. LAA OSI had an average value of 0.45 in AF versus 0.36 in SR, showing a 26% increase. Similarly, the TAWSS was 3.5x10–3 Pa on average over the LAA in AF compared to 1.4x10–3 Pa in SR. Conclusions Patient-specific LA models combining these three quantitative characteristics can be used to predict the higher thrombogenic risk in AF. After further validation, this novel approach for quantitative assessment of AF patient thrombogenicity based on modelling all factors in Virchow's triad can personalise and improve management of AF patients with a risk of stroke. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): UK Engineering and Physical Sciences Research Council

Modified no-touch technique for radio-cephalic arteriovenous fistula increases primary patency and decreases juxta-anastomotic stenosis.

Low primary patency rate is a major problem of radio-cephalic arteriovenous fistula (RC-AVF) creation. Radial artery deviation and reimplantation (RADAR) is associated with low juxta-anastomotic stenosis rate. However, inflow artery stenosis is prominent with RADAR. To further reduce injury to veins and arteries during operation, a modified no-touch technique (MNTT) was used to create RC-AVF. We retrospectively reviewed our prospectively maintained database of patients with end-stage renal disease (ESRD)s undergoing RC-AVF creation for hemodialysis using either the MNTT between January 2021 and January 2022 (MNTT group) or conventional surgical procedure ( end-to-side vein-to-artery anastomosis) between October 2016 and October 2017 (Control group). Patients who chose to undergo RC-AVF surgery underwent standardized preoperative mapping and postoperative fistula evaluations using duplex ultrasound. Additionally, 4D flow MRI data were used to visualize and quantify the hemodynamics of one RC-AVF by MNTT. Outcomes included primary patency, juxta-anastomotic stenosis, and maturation rates. Forty patients underwent RC-AVFs by MNTT, compared to 60 patients in the control group. The MNTT group had a higher primary unassisted patency rate than the control group (p = 0.038). Juxta-anastomotic stenosis (all on the cephalic vein) occurred in 4 (10%) patients who underwent MNTT. RC-AVF maturation rates after 3 months were not different between both groups (maturation rate: 90% and 81.7% in the MNTT and control groups, respectively, p = 0.253). COX regression showed that both conventional AVF surgery (p = 0.031) and smaller cephalic vein diameter (p = 0.034) were associated with higher odds of RC-AVF failure. The AVF flow within the proximal vein remained helical during cardiac cycle. The distribution of wall shear stress (WSS) and oscillatory shear index (OSI) differed from that of conventional surgical AVF. RC-AVF by MNTT increases primary patency rate and decreases juxta-anastomotic stenosis rate. The improvement in hemodynamics may be one of the important reasons for the better patency rate of in the RC-AVF by MNTT group.

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.

Association of Shear Stress with Subsequent Lumen Remodeling in Hemodialysis Arteriovenous Fistulas.

Blood flow-induced wall shear stress is a strong local regulator of vascular remodeling, but its effects on arteriovenous fistula (AVF) remodeling are unclear. In this prospective cohort study, we used computational fluid dynamics simulations and statistical mixed-effects modeling to investigate the associations between wall shear stress and AVF remodeling in 120 participants undergoing AVF creation surgery. Postoperative magnetic resonance imaging data at 1 day, 6 weeks, and 6 months were used to derive current wall shear stress by computational fluid dynamic simulations and to quantify subsequent changes in AVF lumen cross-sectional area at 1-mm intervals along the proximal artery and AVF vein. Combining artery and vein data, prior mean wall shear stress was significantly associated with lumen area expansion. Mean wall shear stress at day 1 was significantly associated with change in lumen area from day 1 to week 6 (11% larger area per interquartile range [IQR] higher mean wall shear stress, 95% confidence interval [95% CI], 5% to 18%; n =101), and mean wall shear stress at 6 weeks was significantly associated with change in lumen area from 6 weeks to month 6 (14% larger area per IQR higher, 95% CI, 3% to 28%; n =52). The association of mean wall shear stress at day 1 with lumen area expansion from day 1 to week 6 differed significantly by diabetes ( P =0.009): 27% (95% CI, 17% to 37%) larger area per IQR higher mean wall shear stress without diabetes and 9% (95% CI, -1% to 19%) with diabetes. Oscillatory shear index at day 1 was significantly associated with change in lumen area from day 1 to week 6 (5% smaller area per IQR higher oscillatory shear index, 95% CI, 3% to 7%), and oscillatory shear index at 6 weeks was significantly associated with change in lumen from 6 weeks to month 6 (7% smaller area per IQR higher oscillatory shear index, 95% CI, 2% to 11%). Wall shear stress spatial gradient was not significantly associated with subsequent remodeling. In a joint model, wall shear stress and oscillatory shear index statistically significantly interacted in their associations with lumen area expansion in a complex nonlinear fashion. Higher wall shear stress and lower oscillatory shear index were associated with greater lumen expansion after AVF creation surgery.

Numerical study of the risk of thrombosis in the left atrial appendage of chicken wing shape in atrial fibrillation.

Atrial fibrillation (AF) is a common and life-threatening disease. For the patients with AF, more than 90% of the thrombi are formed in the left atrial appendage (LAA), thrombus dislodgement can cause vascular embolism, making them is becoming a high-risk group for stroke. Therefore, identifying the patients with high risk of thrombosis is crucial for advanced stroke warning. To better investigate the mechanism behind thrombus formation in the LAA, this study reconstructed the 3-D Left Atrium (LA) models of six AF volunteer patients by corresponding Computed Tomography (CT) images. Combine the advantages of Computational Fluid Dynamics (CFD), the blood flow field in LA both in AF and sinus heart rate states were studied. The risk of thrombus was evaluated based on the blood viscosity, shear rate thrombus prediction model and Time Average Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), and Relative Residence Time (RRT) values. The results showed that the left atrium had lower blood flow velocity and TAWSS values at the LAA in both AF and sinus rhythm, thus the LAA is the most thrombogenic region in the LA. Besides, the RRT value of LAA was generally higher in AF than in sinus rhythm. Therefore, AF carries a higher risk of thrombosis.

The effect of subbranch for the quantification of local hemodynamic environment in the coronary artery: a computed tomography angiography–based computational fluid dynamic analysis

Abstract Background Hemodynamic parameters derived from computed tomography angiography–based computational fluid dynamics (CFD) analysis have been widely used for clinical decision-making and researches to assess the vulnerability of atherosclerotic plaques and explain the initialization and development of atherosclerosis. Subbranches in the CFD model might affect the accuracy of hemodynamic parameters, but the effectiveness has been least quantified. Methods A coronary artery baseline model was generated with focal stenosis at the proximal left anterior descending artery. Nineteen comparing models were created by systematically removing various subbranches to examine the changes in hemodynamic parameters, including time-averaged pressure (TAP), time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and particle relative residence time (RRT). Changes in these parameters were assessed quantitatively around the stenosis and near the region where subbranches were removed. Results The removal of subbranches caused a significant change in outflow rate, and there was generally a decrease in all CFD parameters in the regions of interest with a decrease in outflow rate. The subbranch removal had a significant impact on the calculation of TAWSS, OSI, and RRT, whereas TAP was insensitive to the removal with approximately 0.25% variation in all 19 models. The local effect from removing branch segments generally became negligible after 5 diameters away from the cutting-off position, but the decrease could be affected by other factors, such as a large curvature. Conclusion The outflow rate is a dominant factor for the calculation of TAP, TAWSS, OSI, and RRT. Removal of subbranches has a minor effect on the TAP calculation, but its effect is considerable on the TAWSS, OSI, and RRT. The effect of subbranch removal is limited in a region with 5 local diameters.

Computational analysis of the blood hemodynamic inside internal cerebral aneurysm in the existence of endovascular coiling

The precise evaluations of intracranial aneurysms (IAs) are highly prominent for the treatment and control of aneurysm rupture. Computational fluid dynamic (CFD) simulations based on angiography image is a reliable tool for the recognition of high-risk region and aneurysm status in recent years. In our study, the CFD is used to investigate the impacts of blood hematocrit and coiling techniques on the risk of aneurysm rupture. To do this, wall shear stress (WSS), oscillatory shear index (OSI) and pressure distribution on the wall of an aneurysm are comprehensively evaluated in various coding porosities and blood viscosities. One-way Fluid Solid Interaction (FSI) technique is applied to investigate the non-Newtonian, pulsatile blood stream inside the sac of the aneurysm. Impacts of two coiling porosities and blood hematocrits of 0.3 and 0.5 on blood features inside the sac are also analyzed. The influence of the blood mass flow rate in four different time instants of blood cycles on the size of the high-risk region on the aneurysm wall is demonstrated. Our results show that more than 40% reduction is noticed when the hematocrit (HCT) of blood is reduced from 0.5 to 0.3 in different time instants. Our findings also reveal that decreasing the porosity from 0.96 to 0.74 in the peak systolic stage results in a 28% reduction in the maximum OSI at specific HCT = 0.4.

Effect of lower extremity amputation on cardiovascular hemodynamic environment: An in vitro study

Lower extremity amputation (LEA) was associated with a greater risk of cardiovascular disease, but its hemodynamic mechanisms have not been fully studied. Therefore, to clarify the interrelationship between them, and figure out the potential pathogenesis, the exploration of the hemodynamic environment change of patients after LEA was premeditatedly executed. A near-physiological mock circulatory system (MCS) was employed in the present work to replicate the cardiovascular circulation after LEA in a short time and the unsteady-state numerical simulation was utilized as an auxiliary method to observe the changes of the hemodynamic environment inside the blood vessel. Higher severity of LEA leads to higher peripheral vascular impedance, higher blood pressure, and more obvious redistribution of blood perfusion volume. In addition, higher severity of LEA leads to lower wall shear stress (WSS), higher oscillatory shear index (OSI), and higher relative residence time (RRT) appeared in the infrarenal abdominal aorta and the iliac artery, while these changes are closely related to the higher probability of cardiovascular diseases. Results showed that different degrees of LEA (varying heights, unilateral/bilateral) have diverse effects on the patient's hemodynamic environment. This study explained the potential pathogenesis of cardiovascular diseases after LEA from a hemodynamic perspective and provided a certain reference value for the improvement of the cardiovascular hemodynamic environment and the prevention of cardiovascular diseases in lower extremity amputees.

Risk factors for the rupture of mirror middle cerebral artery aneurysm using computer-assisted semiautomated measurement and hemodynamic analysis

ObjectivesTo identify the morphologic and hemodynamic risk factor of mirror middle cerebral artery (MCA) aneurysms. MethodsWe conducted a retrospective analysis of 40 paired mirror MCA aneurysms. Aneurysms were divided into ruptured and unruptured groups. Seventeen morphological and nine hemodynamic parameters were measured using computer-assisted semiautomated measurement (CASAM) and computer flow dynamic (CFD) simulation. We performed a paired t-test (for normally distributed data) or a paired Wilcoxon rank-sum (for non-normally distributed data) to analyze all parameters between the groups. Multivariate conditional logistic regression analysis identified independent risk factors. The receiver operating characteristic curve was analyzed to acquire the area under the curve (AUC) and the cutoff values of the independent risk factors. ResultsThere were significant differences in morphological and hemodynamic parameters between the ruptured and unruptured mirror aneurysms. The multivariate logistic analysis showed that the greater size (odds ratio [OR] = 9.807, p = 0.003), smaller neck diameter (OR = 0.285, p = 0.018) and maximum oscillatory shear index (OSI) (OR = 0.000001, p = 0.046) were independently correlated with aneurysm rupture. AUCs for size, N. and maximum OSI were 0.794, 0.695, and 0.701, respectively. The cutoff values of the size, neck diameter, and maximum OSI were 6.30, 5.07, and 0.356437, respectively. ConclusionsMorphology and hemodynamics can help predict aneurysm rupture risks. The more significant size, smaller neck diameter and maximum OSI were independent risk factors for the rupture of MCA aneurysms. The variables could aid practical risk evaluation.

The impact of ECMO lower limb cannulation on the aortic flow features under differential blood perfusion conditions

The purpose of this study is to investigate the impact of veno-arterial (VA) ECMO cannulation on hemodynamic distribution and organ perfusion within aorta under differential blood perfusion conditions. The total blood flow volume supplied by failure heart and ECMO keep constant, flow volume ratio of heart output (FVR-HO) increases from 0% to 100% and correspondingly flow volume ratio of ECMO (FVR-ECMO) decreases from 100% to 0%. The flow patterns within aorta, wall shear stress (WSS), oscillatory shear index (OSI), relative retention time (RRT) were analyzed. The locations of oxygenated and de-oxygenated blood mixing region (BMR) was influenced by FVR-HO. With FVR-HO increasing, BMR moves from proximal to distal side of heart. When FVR-HO was 0%, oxygenated blood supplied by ECMO completely perfuses the aortic vessels. High WSS appears in the iliac artery and abdominal aorta vessel walls closed to cannula position. When FVR-HO was in the range of 10%–30%, the BMR was in aortic arch. The higher OSI and RRT were exhibited in ascending aorta and aorta arch. When FVR-HO was 40% and 50%, the BMR was in ventral trunk for systolic period and in aortic arch for diastolic period. The higher OSI and RRT regions enlarge and metastasize to the descending aorta. When FVR-HO was larger than 50%, the BMR was in the downstream region of the renal artery. Of note, when FVR-HO increases from 0% to 100%, the flow ratios in the two renal arteries change from significant different to be closed at systolic period. Peripheral VA-ECMO with various perfusion levels from cardiac output and ECMO has significant effect on aortic flow surrounding. Partial recovery of heart function can impel BMR moves from proximal to distal side of the heart, which may lead to inadequate supply of oxygenated blood to the upper limb and cephalic vessels.

Localized Elevation of Wall Shear Stress Is Linked to Recent Symptoms in Patients with Carotid Stenosis

Background: Estimation of symptomatic and asymptomatic carotid atherosclerosis differences can be the basis for prevention and management of carotid artery stenosis disease. In clinical practice, carotid plaque vulnerability is assessed only on the basis of luminal stenosis. However, the evolution of carotid plaque from an asymptomatic state to a symptomatic one is a complex process and the underlying hemodynamic mechanisms are unknown. We aimed to investigate the differences in hemodynamic parameters between patients with recently symptomatic carotid stenosis and asymptomatic ones. Methods: Hemodynamic simulations were performed on 26 carotid plaques from 25 patients with carotid artery stenosis ≥50%, 16 of whom had recent cerebrovascular ischemic events. Using human-specific flow parameters and 3D reconstruction of carotid computed tomography angiography images, we assessed hemodynamic characteristics such as wall shear stress (WSS), time-averaged WSS (TAWSS), oscillatory shear index, and relative residence time (RRT) during the cardiac cycle in patients with and without symptoms. Results: We found that symptomatic carotid stenosis patients had greater local TAWSS (99.59 ± 26.29 vs. 60.40 ± 20.46 dyn/cm², p = 0.0007) and maximal WSS (116.65 ± 39.11 vs. 68.28 ± 23.67 dyn/cm², p = 0.003), but lower RRT (0.019 ± 0.006 vs. 0.013 ± 0.069 s, p = 0.049), than asymptomatic patients, but this hemodynamic difference was not associated with carotid stenosis severity (p = 0.70). Patients with transient ischemic attack (TIA) or stroke had higher local TAWSS and WSSmax than patients with asymptomatic stenosis (p < 0.05). Subgroup analysis showed that there was no statistical difference in local hemodynamic variables between TIA and stroke patients with carotid artery stenosis. Conclusions: Patients with carotid artery stenosis are more likely to experience acute ischemic cerebrovascular accidents if they have higher WSS. Simultaneous assessment with hemodynamic parameters like WSS along with stenosis severity may aid risk stratification in patients with asymptomatic carotid artery stenosis.

Hemodynamic evaluation of endarterectomy and stenting treatments for carotid web.

A carotid web is a thin, shelf-like luminal protrusion in the internal carotid artery that might cause carotid stenosis and stroke by inducing disturbed flow patterns, thrombosis, and abnormal biomechanical stimulus to the endothelial cells. This study simulated and evaluated how the two main treatments (endarterectomy and stenting) influence hemodynamic environments in the carotid artery and distal carotid siphon arteries, aiming to provide more references for the selection of clinical treatment. The carotid web, endarterectomy, and stenting models were reconstructed based on CT images. The blood flow simulations were conducted, and critical parameters related to thrombosis formation and artery remodeling, including swirling strength, wall shear stress (WSS), vortex Q-criterion, and oscillating shear index (OSI), were analyzed. In the model of the carotid web, obvious recirculation formed distal to the web, accompanied by lower velocity, lower WSS, higher relative resident time (RRT), and higher Q value. While in both two treatment models, the velocity increased and the Q value and RRT decreased at the carotid bifurcation. In addition, both treatments provide more kinetic energy to the distal carotid siphon artery, especially the stenting model. The carotid web can significantly influence the flow environments in the carotid artery. Both endarterectomy and stenting treatments could significantly diminish the side effects of the web and are feasible choices for web patients in terms of hemodynamics. Besides, the treatments for the carotid web would also influence the flow patterns at the distal carotid siphon, especially for the stenting treatment. But more innovational designs are needed to make the minimally invasive stenting treatment more beneficial.

Influence of the flow field and vortex structure of patient-specific abdominal aortic aneurysm with intraluminal thrombus on the arterial wall

ABSTRACT In this study, numerical simulations and experiments were conducted on patient-specific normal abdominal aorta and abdominal aortic aneurysm (AAA) with intraluminal thrombus (ILT) models, which were reconstructed from computed tomography angiography (CTA) images published online. A scale-adaptive simulation (SAS) of the abdominal aortic aneurysm with a posterior eccentric thrombus was performed and the reliability of the numerical simulation was verified by 2D particle image velocimetry (PIV) experimental results. The distribution of wall shear stress (WSS), oscillatory shear index (OSI), and relative residence time (RRT) of the normal abdominal aorta and AAA were compared and discussed systematically according to the numerical simulation results under rest and exercise conditions. Numerical results indicated that ILT deposition positions were accompanied by low WSS, high OSI, and high RRT regions and were characterized by small vortex groups, which was due to the fragmentation of large vortex structures. The distribution law of the AAA wall parameters has an obvious correlation with the nearby vortex structure formation, development, fragmentation and dissipation. It was also found that high TAWSS, low OSI, and low RRT regions present in the middle and lower aneurysm walls under exercise condition reduce the risk of ILT formation and development.

Development of a computational fluid dynamic model to investigate the hemodynamic impact of REBOA.

Background: Resuscitative endovascular balloon occlusion of the aorta (REBOA) is a lifesaving intervention for major truncal hemorrhage. Balloon-tipped arterial catheters are inserted via the femoral artery to create a temporary occlusion of the aorta, which minimizes the rate of internal bleeding until definitive surgery can be conducted. There is growing concern over the resultant hypoperfusion and potential damage to tissues and organs downstream of REBOA. To better understand the acute hemodynamic changes imposed by REBOA, we developed a three-dimensional computational fluid dynamic (CFD) model under normal, hemorrhage, and aortic occlusion conditions. The goal was to characterize the acute hemodynamic changes and identify regions within the aortic vascular tree susceptible to abnormal flow and shear stress. Methods: Hemodynamic data from established porcine hemorrhage models were used to build a CFD model. Swine underwent 20% controlled hemorrhage and were randomized to receive a full or partial aortic occlusion. Using CT scans, we generated a pig-specific aortic geometry and imposed physiologically relevant inlet flow and outlet pressure boundary conditions to match in vivo data. By assuming non-Newtonian fluid properties, pressure, velocity, and shear stresses were quantified over a cardiac cycle. Results: We observed a significant rise in blood pressure (∼147 mmHg) proximal to REBOA, which resulted in increased flow and shear stress within the ascending aorta. Specifically, we observed high levels of shear stress within the subclavian arteries (22.75 Pa). Alternatively, at the site of full REBOA, wall shear stress was low (0.04 ± 9.07E-4 Pa), but flow oscillations were high (oscillatory shear index of 0.31). Comparatively, partial REBOA elevated shear levels to 84.14 ± 19.50 Pa and reduced flow oscillations. Our numerical simulations were congruent within 5% of averaged porcine experimental data over a cardiac cycle. Conclusion: This CFD model is the first to our knowledge to quantify the acute hemodynamic changes imposed by REBOA. We identified areas of low shear stress near the site of occlusion and high shear stress in the subclavian arteries. Future studies are needed to determine the optimal design parameters of endovascular hemorrhage control devices that can minimize flow perturbations and areas of high shear.

Influence of blood pressure and rheology on oscillatory shear index and wall shear stress in the carotid artery

Atherosclerosis is a localized complication dependent on both the rheology and the arterial response to blood pressure. Fluid–structure interaction (FSI) study can be effectively used to understand the local haemodynamics and study the development and progression of atherosclerosis. Although numerical investigations of atherosclerosis are well documented, research on the influence of blood pressure as a result of the response to physio–social factors like anxiety, mental stress, and exercise is scarce. In this work, a three-dimensional (3D) Fluid–Structure Interaction (FSI) study was carried out for normal and stenosed patient-specific carotid artery models. Haemodynamic parameters such as Wall Shear Stress (WSS) and Oscillatory Shear Index (OSI) are evaluated for normal and hypertension conditions. The Carreau–Yasuda blood viscosity model was used in the FSI simulations, and the results are compared with the Newtonian model. The results reveal that high blood pressure increases the peripheral resistance, thereby reducing the WSS. Higher OSI occurs in the region with high flow recirculation. Variation of WSS due to changes in blood pressure and blood viscosity is important in understanding the haemodynamics of carotid arteries. This study demonstrates the potential of FSI to understand the causes of atherosclerosis due to altered blood pressures.