Time-averaged Wall Shear Stress Research Articles

Type B Aortic Dissection in Marfan Patients after the David Procedure: Insights from Patient-Specific Simulation

ObjectiveAn elevated risk of acute type B aortic dissection (ATBAD) exists in Marfan syndrome (MFS) patients after the David procedure. This study explores hemodynamic changes in the descending aorta post-surgery. MethodsA single-center retrospective review identified 5 MFS patients who experienced ATBAD within 6 years post-David procedure, alongside 5 matched MFS patients without dissection >6 years post-surgery. Baseline and post-operative CT/MRI scans were analyzed for aortic geometry reconstruction. Computational fluid dynamics simulations evaluated pre- and post-operative hemodynamics. ResultsPatients with ATBAD showed lower blood flow velocities, increased vortices, and altered velocity profiles in the proximal descending aorta compared to controls. Pre-operatively, median Time-averaged wall shear stress (TAWSS) in the descending aorta was lower in ATBAD patients (Control: 1.76 [1.50, 2.83] Pa, Dissection: 1.16 [1.06, 1.30] Pa, p=0.047). Post-surgery, neither group had significant TAWSS changes (Dissection: p=0.69, Control: p=0.53). Localized analysis revealed surgery-induced TAWSS increases near the subclavian artery in the dissection group (range: +0.30 to +1.05 Pa, each comparison, p<0.05). No such changes were observed in controls. Oscillatory shear index (OSI) and Relative residence time (RRT) were higher in ATBAD patients pre- and post-surgery versus controls. ConclusionHemodynamics likely play a role in post-David procedure ATBAD. Further investigation into aortic geometry, hemodynamics, and post-operative ATBAD is vital for enhancing outcomes and refining surgical strategies in MFS patients.

Modelling lower-limb peripheral arterial disease using clinically available datasets: impact of inflow boundary conditions on hemodynamic indices for restenosis prediction

Modelling lower-limb peripheral arterial disease using clinically available datasets: impact of inflow boundary conditions on hemodynamic indices for restenosis prediction

The Role of Wall Mechanics in the Hemodynamics of a Realistic Abdominal Aortic Aneurysm: A Fluid-Structure Interaction Study

Abdominal aortic aneurysm (AAA) can lead to high mortality rates and further complications such as stroke or heart attack due to the risk of rupture and thrombosis. Wall mechanics play a crucial role in the development and progression of aneurysms. This study investigated the effects of wall mechanics on hemodynamic parameters in AAA to understand the risk of rupture and thrombosis. The impact of three aortic wall models (rigid, linear elastic, and hyperelastic) on structural and hemodynamic parameters was examined using CFD and FSI techniques. The blood was modeled using the Carreau non-Newtonian model, and the flow was simulated using the k-ω model. Physiological pulses were used for the velocity at the inlet and the pressure at the outlet. The results demonstrated close similarity between the predictions of the linear elastic and hyperelastic models, in contrast to the somewhat different results of the rigid model. The hyperelastic model predicted higher deformation and von Mises stress levels than the elastic model, although the difference in stress predictions was smaller than the difference in deformation predictions. The rigid model evaluated the time-averaged wall shear stress and oscillatory shear index higher than the other two models in the aneurysmal area but with a lower relative residence time. In general, the hyperelastic model predicted a higher risk of rupture than linear elastic models and a higher risk of thrombus formation than the other two models. The rigid model had the most optimistic prediction.

Assessing the influence of aneurysm dimensions on hemodynamic patterns and wall deformation dynamics for predicting rupture risk

Cerebral aneurysms are among the most dangerous cardiovascular diseases which display no symptoms prior to reaching critical conditions. As cerebral aneurysms are deadly diseases with a very small treatment window after reaching the critical stage, numerical investigations of this phenomenon are commonly used to assess the risk of rupture. In this study, the fluid-structure interaction (FSI) method is used to analyze the effects of aneurysm size on hemodynamic factors predicting rupture in three aneurysms of different geometries, at the same location, and using the same boundary conditions. In the present study, the aneurysms experience TAWSS at values under 2 Pa in incremented areas as the aneurysmal sizes increase, this is while the relatively larger distribution of high TAWSS (as high as 20 Pa) regions are perceived in smaller aneurysms. Furthermore, the maximum OSI stands at below 0.05 in the smaller cases while the larger case experiences a maximum OSI as high as 0.2, which is considered a predictive parameter for rupture. The vortex core lines experience discontinuities with increased aneurysmal size, which is in agreement with the development of flow complexities with size. The hemodynamics factors such as the time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and vortex core line investigated in this study, suggest that greater size can be considered a major risk factor for rupture. In addition to that, we have found that the displacement trend of the aneurysm changes as size increases; developing more in the dome rather than the aneurysmal sac. This change in trend might also present a potential to be used as a predictive parameter.

Changes in aorta hemodynamics in Left-Right Type 1 bicuspid aortic valve patients after replacement with bioprosthetic valves: An in-silico study.

Bicuspid aortic valve (BAV) is the most common cardiac congenital abnormality with a high rate of concomitant aortic valve and ascending aorta (AAo) pathologic changes throughout the patient's lifetime. The etiology of BAV-related aortopathy was historically believed to be genetic. However, recent studies theorize that adverse hemodynamics secondary to BAVs also contribute to aortopathy, but their precise role, specifically, that of wall shear stress (WSS) magnitude and directionality remains controversial. Moreover, the primary therapeutic option for BAV patients is aortic valve replacement (AVR), but the role of improved post-AVR hemodynamics on aortopathy progression is also not well-understood. To address these issues, this study employs a computational fluid dynamics model to simulate personalized AAo hemodynamics before and after TAVR for a small cohort of 6 Left-Right fused BAV patients. Regional distributions of five hemodynamic metrics, namely, time-averaged wall shear stress (TAWSS) and oscillating shear index (OSI), divergence of wall shear (DWSS), helicity flux integral & endothelial cell activation potential (ECAP), which are hypothesized to be associated with potential aortic injury are computed in the root, proximal and distal ascending aorta. BAVs are characterized by strong, eccentric jets, with peak velocities exceeding 4 m/s and axially circulating flow away from the jets. Such conditions result in focused WSS loading along jet attachment regions on the lumen boundary and weaker, oscillating WSS on other regions. The jet attachment regions also show alternating streaks of positive and negative DWSS, which may increase risk for local tissue stretching. Large WSS magnitudes, strong helical flows and circumferential WSS have been previously implicated in the progression of BAV aortopathy. Post-intervention hemodynamics exhibit weaker, less eccentric jets. Significant reductions are observed in flow helicity, TAWSS and DWSS in localized regions of the proximal AAo. On the other hand, OSI increases post-intervention and ECAP is observed to be low in both pre- and post-intervention scenarios, although significant increases are also observed in this ECAP. These results indicate a significant alleviation of pathological hemodynamics post AVR.

Analysis of Aortic Arch Hemodynamics With Simulated Bird's Beak Effects.

The objective of this study was to investigate the flow effects in different degrees of thoracic aortic stent graft protrusion extension by creating bird beak effect simulations using accurate 3D geometry and a realistic, nonlinear, elastic biomechanical model using computer-aided software SolidWorks. Segmentation in 3D of an aortic arch from a computed tomography (CT) scan of a real-life patient was performed using SolidWorks. A parametric analysis of three models was performed: (A) Aortic arch with no stent, (B) 3mm bird-beak configuration, and (C) 6.5mm bird-beak configuration. Flow velocity, pressure, vorticity, wall shear stress (WSS), and time average WSS were assessed. The flow velocity in Model A remained relatively constant and low in the area of the ostium of the brachiocephalic artery and doubled in the left subclavian artery. On the contrary, Models B and C showed a decrease in velocity of 52.3 % in the left subclavian artery. Furthermore, Model B showed a drop in velocity of 82.7% below the bird-beak area, whereas Model C showed a decline of 80.9% in this area. The pressure inside the supra-aortic branches was higher in Model B and C compared with Model A. In Model A, vorticity only appeared at the level of the descending aorta, with low to non-vorticity in the aortic arch. In contrast, Models B and C had an average vorticity of 241.4Hz within the bird beak area. Regarding WSS, Model A, and Model B shared similar WSS in the peak systolic phase, in the aortic arch, and the bird beak area, whereas Model C had an increased WSS by 5Pa on average at these zones. In the present simulations' lower velocities, higher pressures, vortices, and WSS were observed around the bird beak zone, the aortic arch, and the supra-aortic vessels.

Influence of circle of Willis modeling on hemodynamic parameters in anterior communicating artery aneurysms and recommendations for model selection

Computational fluid dynamics (CFD) has been utilized to calculate hemodynamic parameters in anterior communicating artery aneurysm (AComA), which is located at a junction between left and right A1 and A2 segments. However, complete or half circle of Willis (CoW) models are used indiscriminately. This study aims to suggest recommendations for determining suitable CoW model. Five patient-specific CoW models with AComA were used, and each model was divided into complete, left-half, and right-half models. After validating the CFD using a flow experiment, the hemodynamic parameters and flow patterns in five AComAs were compared. In four out of five cases, inflow from one A1 side had a dominant influence on the AComA, while both left and right A1 sides affected the AComA in the remaining case. Also, the average difference in time-averaged wall shear stress between the complete and half models for four cases was 4.6%, but it was 62% in the other case. The differences in the vascular resistances of left and right A1 and A2 segments greatly influenced the flow patterns in the AComA. These results may help to enhance clinicians’ understanding of blood flow in the brain, leading to improvements in diagnosis and treatment of cerebral aneurysms.

Computational Analysis of Blood Flow in Healthy Pulmonary Arteries in Comparison to Repaired Tetralogy of Fallot Results: A Small Cohort Study

Characterization of the physiological hemodynamic environment in normal pulmonary arteries is a key factor in understanding pathological conditions. This study aimed to analyze the morphology and hemodynamics in the healthy adult pulmonary bifurcation in comparison to age-matched repaired Tetralogy of Fallot (rTOF) geometries. The pulmonary trunk of five healthy volunteers was reconstructed from 4D Flow-MRI data and was compared to rTOF results. Subject-specific boundary conditions were assigned in both the inlet and outlets of the models, and flow characteristics were analyzed computationally. The morphological and flow features were consistent among the healthy geometries, highlighting the ability of an averaged geometry derived from this small cohort to capture the main flow characteristics. A slightly higher mean time-averaged wall shear stress (TAWSS) was found in the right pulmonary artery, which was also the branch with a higher mean curvature and local Reynolds number. Compared to rTOF results, the averaged healthy geometry demonstrated more than an 8-fold lower value in TAWSS, with the individual patient-specific healthy volunteers showing further reduced TAWSS than the rTOF patients. These observations could be useful in clinical assessment and decision making based on hemodynamic indices.

CFD Based on The Visualisation of Aortic Valve Mechanism in Aortic Valve Stenosis for Risk Prediction at The Peak Velocity

Aortic valve disease plays a crucial role in the development of cardiovascular disease (CVD), leading to increased rates of mortality and morbidity. Two diseases, aortic valve regurgitation and aortic valve stenosis are known to occur in the aortic valve. However, aortic valve stenosis is gaining attention due to its severe impact on the patient. The malfunction of the aortic valve might be affected by blood flow, which leads to stenosis. This study aims to investigate the blood flow re-circulation on the aortic valve in different stenotic regions when the blood’s velocity reaches the pick flow of the time in the systole phases. Four different models of aortic valve stenotic are designed using computer-aided design (CAD) software. The computational fluid dynamics (CFD) approach governed by the Navier-Stokes equation is imposed to identify the characteristics of the blood backflow at the left ventricle. Several hemodynamic factors are considered, such as time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI) and relative residence time (RRT). The blood flow characteristic is expected to be chaotic, especially at the highest percentages of aortic valve stenosis, presenting the worst condition to the heart. This finding supports healthcare providers in foreseeing the deterioration of the patient’s condition and opting for aorta valve surgery replacement.

Are hemodynamics responsible for inflammatory changes in venous vessel walls? A quantitative study of wall-enhancing intracranial arteriovenous malformation draining veins.

Signal enhancement of vascular walls on vessel wall MRI might be a biomarker for inflammation. It has been theorized that contrast enhancement on vessel wall imaging (VWI) in draining veins of intracranial arteriovenous malformations (AVMs) may be associated with disease progression and development of venous stenosis. The aim of this study was to investigate the relationship between vessel wall enhancement and hemodynamic stressors along AVM draining veins. Eight AVM patients with 15 draining veins visualized on VWI were included. Based on MR venography data, patient-specific 3D surface models of the venous anatomy distal to the nidus were segmented. The enhanced vascular wall regions were manually extracted and mapped onto the venous surface models after registration of image data. Using image-based blood flow simulations applying patient-specific boundary conditions based on phase-contrast quantitative MR angiography, hemodynamics were investigated in the enhanced vasculature. For the shear-related parameters, time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT) were calculated. Velocity, oscillatory velocity index (OVI), and vorticity were extracted for the intraluminal flow-related hemodynamics. Visual observations demonstrated overlap of enhancement with local lower shear stresses resulting from decreased velocities. Thus, higher RRT values were measured in the enhanced areas. Furthermore, nonenhancing draining veins showed on average slightly higher flow velocities and TAWSS. Significant decreases of 55% (p = 0.03) for TAWSS and of 24% (p = 0.03) for vorticity were identified in enhanced areas compared with near distal and proximal domains. Velocity magnitude in the enhanced region showed a nonsignificant decrease of 14% (p = 0.06). Furthermore, increases were present in the OSI (32%, p = 0.3), RRT (25%, p = 0.15), and OVI (26%, p = 0.3) in enhanced vessel sections, although the differences were not significant. This novel multimodal investigation of hemodynamics in AVM draining veins allows for precise prediction of occurring shear- and flow-related phenomena in enhanced vessel walls. These findings may suggest low shear to be a local predisposing factor for venous stenosis in AVMs.

Assessing the impact of tear direction in coronary artery dissection on thrombosis development: A hemodynamic computational study

ObjectiveIatrogenic coronary artery dissection is a complication of coronary intimal injury and dissection due to improper catheter manipulation. The impact of tear direction on the prognosis of coronary artery dissection (CAD) remains unclear. This study examines the hemodynamic effects of different tear directions (transverse and longitudinal) of CAD and evaluates the risk of thrombosis, rupture and further dilatation of CAD. MethodsTwo types of CAD models (Type I: transverse tear, Type II: longitudinal tear) were reconstructed from the aorto-coronary CTA dataset of 8 healthy cases. Four WSS-based indicators were analyzed, including time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), and cross flow index (CFI). A thrombus growth model was also introduced to predict the trend of thrombus growth in CAD with two different tear directions. ResultsFor most of the WSS-based indicators, including TAWSS, RRT, and CFI, no statistically significant differences were observed across the CAD models with varying tear directions, except for OSI, where a significant difference was noted (p < 0.05). Meanwhile, in terms of thrombus growth, the thrombus growing at the tear of the Type I (transverse tear) CAD model extended into the true lumen earlier than that of the Type II (longitudinal tear) model. ConclusionsNumerical simulations suggest that: (1) The CAD with transverse tear have a high risk of further tearing of the dissection at the distal end of the tear. (2) The CAD with longitudinal tear create a hemodynamic environment characterized by low TAWSS and high OSI in the false lumen, which may additionally increase the risk of vessel wall injury. (3) The CAD with transverse tear may have a higher risk of thrombosis and coronary obstruction and myocardial ischemia in the early phase of the dissection.

Spatiotemporal analysis of the effects of exercise on the hemodynamics of the aorta in hypertensive rats using fluid-structure interaction simulation

Abstract Background and Objective Hemodynamic changes that lead to increased blood pressure represent the main drivers of organ damage in hypertension. Prolonged increases to blood pressure can lead to vascular remodeling, which also affects vascular hemodynamics during the pathogenesis of hypertension. Exercise is beneficial for relieving hypertension, however the mechanistic link between exercise training and how it influences hemodynamics in the context of hypertension is not well understood. Methods n exercise model was developed using spontaneously hypertensive rats (SHR) subject to a 12-week treadmill training regime. The heart rates and blood pressures of rats were measured using the tail cuff method, while micro-computed tomography (CT) scanning was used to develop three-dimensional structures of rat aorta, and ultrasound was used to detect rat aortic blood flow and changes to vessel wall structures. Computational fluid dynamics (CFD) and fluid-structure interaction (FSI) models were used to simulate and measure hemodynamic parameters of the rat aortic vessels. In parallel, Masson staining was performed on fixed samples of blood vessels to investigate collagen volume fraction. Hypertensive rats in the sedentary and long-term exercise training groups were subjected to a single bout exercise training, and their aortic hemodynamic parameters were analyzed before, 5 min, 24 h, and 72 h after the single bout exercise. Results Of the two models, in comparison to actual ultrasonic measurement values recorded, we found that numerical simulation results from the FSI model could more accurately model blood flow in the ascending aorta of hypertensive rats, compared to the CFD model. Moreover, longterm exercise training improved local hemodynamic parameters of blood vessels, and led to improvements in adverse hemodynamic features documented, including time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT). Longterm exercise training of SHR also improved local vascular collagen deposition in the aorta, while improvements in vascular remodeling were also correlated with favorable hemodynamic parameters. Compared with sedentary SHR, signals for low TAWSS regions of the aortic arch in SHR on the long-term exercise regime shifted to the position of the ascending aorta after a single bout of exercise. Conclusions This study demonstrates that FSI is informative to study the spatiotemporal effects of long-term exercise training on hemodynamic changes within the aortas of hypertensive rats, and that long-term exercise is beneficial through its effects to modulate vascular hemodynamics in hypertension.

Evaluation of Hemodynamic Properties After Chimney and Fenestrated Endovascular Aneurysm Repair

ObjectivesFenestrated (FEVAR) and chimney (ChEVAR) endovascular aortic repair have been applied in anatomically suitable complex aortic aneurysms. However, local hemodynamic changes may occur after repair. This study aimed to compare FEVAR’s and ChEVAR’s hemodynamic properties, focusing on visceral arteries. MethodsPre- and post-operative computed tomography angiographies (CTAs) have been used to reconstruct patient-based models. Data of three patients, for each modality, were analyzed. Following geometric reconstruction, computational fluid dynamics (CFD) simulations were used to extract near-wall and intravascular hemodynamic indicators, as pressure drops, velocity, wall shear stress (WSS), time average wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT) and local normalized helicity (LNH). ResultsAn overall improvement in hemodynamics was detected after repair, with either technique. Preoperatively, a disturbed pro-thrombotic WSS profile was recorded in several zones of the sac. The LNH results showed a better organization of the helical structures at post-operative setting, decreasing thrombus formation, with both modalities. Similarly, TAWSS increased and OSI decreased post-operatively, signaling non-disturbed blood flow. The RRT was locally reduced. The flow in visceral arteries tended to be more streamlined in ChEVAR, compared to evident recirculation regions at renal and superior mesenteric artery fenestrations (p=0.06). ConclusionChEVAR and FEVAR seem to improve hemodynamics towards normal values with a reduction of recirculation zones in the main graft and aortic branches. Visceral artery flow comparison revealed that ChEVAR tended to present lower recirculation regions at parallel grafts’ entries while FEVAR showed less intense flow regurgitation in visceral stents.

Design of experiment approach to identify the dominant geometrical feature of left coronary artery influencing atherosclerosis

Background and Objective. Coronary artery geometry heavily influences local hemodynamics, potentially leading to atherosclerosis. Consequently, the unique geometrical configuration of an individual by birth can be associated with future risk of atherosclerosis. Although current researches focus on exploring the relationship between local hemodynamics and coronary artery geometry, this study aims to identify the order of influence of the geometrical features through systematic experiments, which can reveal the dominant geometrical feature for future risk assessment. Methods. According to Taguchi’s method of design of experiment (DoE), the left main stem (LMS) length (l LMS), curvature (k LMS), diameter (d LMS) and the bifurcation angle between left anterior descending (LAD) and left circumflex (LCx) artery (α LAD-LCx) of two reconstructed patient-specific left coronary arteries (LCA) were varied in three levels to create L9 orthogonal array. Computational fluid dynamic (CFD) simulations with physiological boundary conditions were performed on the resulting eighteen LCA models. Average helicity intensity (h 2) and relative atheroprone area (RAA) of near-wall hemodynamic descriptors were analyzed. Results. The proximal LAD (LAD proximal) was identified to be the most atheroprone region of the left coronary artery due to higher h 2, large RAA of time averaged wall shear stress (TAWSS < 0.4 Pa), oscillatory shear index (OSI ∼ 0.5) and relative residence time (RRT > 4.17 Pa−1). In both patient-specific cases, based on h 2 and TAWSS, d lms is the dominant geometric parameter while based on OSI and RRT, α LAD-LCx is the dominant one influencing hemodynamic condition in proximal LAD (p < 0.05). Based on RRT, the rank of the geometrical factors is: α LAD-LCx > d LMS > l LMS > k LMS, indicating that α LAD-LCx is the most dominant geometrical factor affecting hemodynamics at proximal LAD which may influence atherosclerosis. Conclusion. The proposed identification of the rank of geometrical features of LCA and the dominant feature may assist clinicians in predicting the possibility of atherosclerosis, of an individual, long before it will occur. This study can further be translated to be used to rank the influence of several arterial geometrical features at different arterial locations to explore detailed relationships between the arterial geometrical features and local hemodynamics.

Surgical Modulation of Pulmonary Artery Shear Stress: A Patient-Specific CFD Analysis of the Norwood Procedure.

This study created 3D CFD models of the Norwood procedure for hypoplastic left heart syndrome (HLHS) using standard angiography and echocardiogram data to investigate the impact of shunt characteristics on pulmonary artery (PA) hemodynamics. Leveraging routine clinical data offers advantages such as availability and cost-effectiveness without subjecting patients to additional invasive procedures. Patient-specific geometries of the intrathoracic arteries of two Norwood patients were generated from biplane cineangiograms. "Virtual surgery" was then performed to simulate the hemodynamics of alternative PA shunt configurations, including shunt type (modified Blalock-Thomas-Taussig shunt (mBTTS) vs. right ventricle-to-pulmonary artery shunt (RVPAS)), shunt diameter, and pulmonary artery anastomosis angle. Left-right pulmonary flow differential, Qp/Qs, time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) were evaluated. There was strong agreement between clinically measured data and CFD model output throughout the patient-specific models. Geometries with a RVPAS tended toward more balanced left-right pulmonary flow, lower Qp/Qs, and greater TAWSS and OSI than models with a mBTTS. For both shunt types, larger shunts resulted in a higher Qp/Qs and higher TAWSS, with minimal effect on OSI. Low TAWSS areas correlated with regions of low flow and changing the PA-shunt anastomosis angle to face toward low TAWSS regions increased TAWSS. Excellent correlation between clinically measured and CFD model data shows that 3D CFD models of HLHS Norwood can be developed using standard angiography and echocardiographic data. The CFD analysis also revealed consistent changes in PA TAWSS, flow differential, and OSI as a function of shunt characteristics.

Study of the mechanism of action of sand therapy on atherosclerosis based on the two-phase flow-Casson model.

Sand therapy is a non-pharmacological physiotherapy method that uses the natural environment and resources of Xinjiang to treat through the heat transfer and magnetic effects of sand. Employing the two-phase flow-Casson blood flow model, we investigate the mechanism of atherosclerosis prevention via sand therapy, offering a biomechanical theoretical rationale for the prevention of atherosclerosis through sand therapy via the prism of computational fluid dynamics (CFD). Sand therapy experiments were conducted to obtain popliteal artery blood flow velocity, and blood was considered as a two-phase flow composed of plasma and red blood cells, and CFD method was applied to analyze the hemodynamic effects of Casson's blood viscosity model before and after sand therapy. (1) The blood flow velocity increased by 0.24 m/s and 0.04 m/s at peak systolic and diastolic phases, respectively, after sand therapy; the axial velocity of blood vessels increased by 28.56% after sand therapy. (2) The average red blood cell viscosity decreased by 0.00014 Pa ⋅ s after sand therapy. (3) The low wall shear stress increased by 1.09Pa and the high wall shear stress reached 41.47Pa after sand therapy. (4) The time-averaged wall shear stress, shear oscillation index and relative retention time were reduced after sand therapy. The increase of blood flow velocity after sand therapy can reduce the excessive deposition of cholesterol and other substances, the decrease of erythrocyte viscosity is beneficial to the migration of erythrocytes to the vascular center, the increase of low wall shear stress has a positive effect on the prevention of atherosclerosis, and the decrease of time-averaged wall shear stress, shear oscillation index and relative retention time can reduce the occurrence of thrombosis.

A real-time patient-specific treatment strategy for enhanced external counterpulsation.

Diastolic/systolic blood pressure ratio (D/S) ≥ 1.2 is the gold standard of enhanced external counterpulsation (EECP) treatment, but it does not show a clear clinical correspondence with the configuration of the EECP mode. As such, a single target results in different treatment effects in different individuals. The local haemodynamic effect (wall shear stress, WSS) of EECP on vascular endothelial cells is conducive to promote the growth of collateral circulation vessels and restore the blood supply distal to the stenosis lesion. Considering the haemodynamic effects of WSS on human arteries, this study developed a real-time patient-specific treatment strategy of EECP for patients with cardio-cerebrovascular diseases. Based on patient-specific haemodynamic data from 113 individuals, an optimization algorithm was developed to achieve the individualization of a 0D lumped-parameter model of the human circulatory system, thereby simulating the patient-specific global haemodynamic effects. 0D/3D coupled cardio-cerebrovascular models of two subjects were established to simulate the local WSS. We then established statistical models to evaluate clinically unmeasurable WSS based on measurable global haemodynamic indicators. With the aim of attaining appropriate area- and time-averaged WSS (ATAWSS, 4-7 Pa), as evaluated by global haemodynamic indicators, a closed-loop feedback tuning method was developed to provide patient-specific EECP treatment strategies. Results showed that for clinical data collected from 113 individuals, the individualized 0D model can accurately simulate patient-specific global haemodynamic effects (average error <5%). Based on two subjects, the statistical models can be used to evaluate local ATAWSS (error <6%) for coronary arteries and for cerebral arteries. An EECP mode planned by the patient-specific treatment strategy can promote an appropriate ATAWSS within a 16 s calculation time. The real-time patient-specific treatment strategy of EECP is expected to improve the long-term outcome for each patient and have potential clinical significance.

The impact of contrast retention on thrombus formation risks in patients with atrial fibrillation: A numerical study

BackgroundContrast retention (CR) is an important predictor of left atrial appendage thrombus (LAAT) and stroke in patients with non-valvular atrial fibrillation (AF). We sought to explore the underlying mechanisms of CR using computational fluid dynamic (CFD) simulations. MethodsA total of 12 patients with AF who underwent both cardiac computed tomography angiography (CTA) and transesophageal echocardiography (TEE) before left atrial appendage occlusion (LAAO) were included in the study. The patients were allocated into the CR group or non-CR group based on left atrial appendage (LAA) angiography. Patient-specific models were reconstructed to evaluate time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), and endothelial cell activation potential (ECAP). Additionally, the incidence of thrombosis was predicted using residence time (RT) at different time-points. ResultsTAWSS was lower [median (Interquartile Range) 0.27 (0.19–0.47) vs 1.35 (0.92–1.79), p < 0.001] in LAA compared to left atrium. In contrast, RRT [1438 (409.70–13869) vs 2.23 (1.81–3.14), p < 0.001] and ECAP [122.70 (30.01–625.70) vs 0.19 (0.16–0.27), p < 0.001)] was higher in the LAA. The patients in the CR group had significantly higher RRT [(mean ± SD) 16274 ± 11797 vs 639.70 ± 595.20, p = 0.009] and ECAP [610.80 ± 365.30 vs 54.26 ± 54.38, p = 0.004] in the LAA compared to the non-CR group. Additionally, patients with CR had a wider range of thrombus-prone regions [0.44(0.27–0.66)% vs 0.05(0.03–0.27)%, p = 0.009] at the end of the 15th cardiac cycle. ConclusionsThese findings suggest that CR might be an indicator of high-risk thrombus formation in the LAA. And CT-based CFD simulation may be a feasible substitute for the evaluation of LAA thrombotic risk in patients with AF, especially in patients with CR.

In silico parametric analysis of femoro-jugular venovenous ECMO and return cannula dynamics

Background: Increasingly, computational fluid dynamics (CFD) is helping explore the impact of variables like: cannula design/size/position/flow rate and patient physiology on venovenous (VV) extracorporeal membrane oxygenation (ECMO). Here we use a CFD model to determine what role cardiac output (CO) plays and to analyse return cannula dynamics. Methods: Using a patient-averaged model of the right atrium and venae cava, we virtually inserted a 19Fr return cannula and a 25Fr drainage cannula. Running large eddy simulations, we assessed cardiac output at: 3.5–6.5 L/min and ECMO flow rate at: 2–6 L/min. We analysed recirculation fraction (Rf), time-averaged wall shear stress (TAWSS), pressure, velocity, and turbulent kinetic energy (TKE) and extracorporeal flow fraction (EFF = ECMO flow rate/CO). Results: Increased ECMO flow rate and decreased CO (high EFF) led to increased Rf (R = 0.98, log fit). Negative pressures developed in the venae cavae at low CO and high ECMO flow (high CR). Mean return cannula TAWSS was >10 Pa for all ECMO flow rates, with majority of the flow exiting the tip (94.0–95.8 %). Conclusions: Our results underpin the strong impact of CO on VV ECMO. A simple metric like EFF, once supported by clinical data, might help predict Rf for a patient at a given ECMO flow rate. The return cannula imparts high shear stresses on the blood, largely a result of the internal diameter.

Exercise mitigates flow recirculation and activates metabolic transducer SCD1 to catalyze vascular protective metabolites.

Exercise promotes pulsatile shear stress in the arterial circulation and ameliorates cardiometabolic diseases. However, exercise-mediated metabolic transducers for vascular protection remain under-investigated. Untargeted metabolomic analysis demonstrated that wild-type mice undergoing voluntary wheel running exercise expressed increased endothelial stearoyl-CoA desaturase 1 (SCD1) that catalyzes anti-inflammatory lipid metabolites, namely, oleic (OA) and palmitoleic acids (PA), to mitigate NF-κB-mediated inflammatory responses. In silico analysis revealed that exercise augmented time-averaged wall shear stress but mitigated flow recirculation and oscillatory shear index in the lesser curvature of the mouse aortic arch. Following exercise, endothelial Scd1-deleted mice (Ldlr-/- Scd1EC-/-) on high-fat diet developed persistent VCAM1-positive endothelium in the lesser curvature and the descending aorta, whereas SCD1 overexpression via adenovirus transfection mitigated endoplasmic reticulum stress and inflammatory biomarkers. Single-cell transcriptomics of the aorta identified Scd1-positive and Vcam1-negative endothelial subclusters interacting with other candidate genes. Thus, exercise mitigates flow recirculation and activates endothelial SCD1 to catalyze OA and PA for vascular endothelial protection.