High wall shear stress and spatial gradients in vascular pathology: a review

Characterization of Post-Operative Hemodynamics Following the Norwood Procedure Using Population Data and Multi-Scale Modeling

Children with hypoplastic left heart syndrome (HLHS) must undergo multiple surgical stages to reconstruct the anatomy to a sustainable single ventricle system. Stage I palliation, or the Norwood procedure, provides circulation to both pulmonary and systemic vasculature. The aorta is reconstructed and attached to the right ventricle and a fraction of systemic flow is redirected to the pulmonary arteries (PAs) through a systemic-to-PA shunt. Despite abundant hemodynamic data available 4-5 months after Norwood palliation, data is very scarce immediately following stage I. This data is critical in determining post-operative success. In this work, we combined population data and computational fluid dynamics (CFD) to characterize hemodynamics immediately following stage I (post-stage I) and prior to stage II palliation (pre-stage II). A patient-specific model was constructed as a baseline geometry, which was then scaled to reflect population-based morphological data at both time-points. Population-based hemodynamic data was then used to calibrate each model to reproduce blood flow representative of HLHS patients. The post-stage I simulation produced a PA pressure of 22 mmHg and high-frequency oscillations within the flow field indicating highly disturbed hemodynamics. Despite PA mean pressure dropping to 14 mmHg, the pre-stage II model also produced high-frequency flow components and PA wall shear stress increases. These suboptimal conditions may be necessary to ensure adequate PA flow throughout the pre-stage II period, as the shunt becomes relatively smaller compared to the patient's somatic growth. In the future, CFD can be used to optimize shunt design and minimize these suboptimal conditions.

Microbiota-Host Immunity Communication in Neurodegenerative Disorders: Bioengineering Challenges for In Vitro Modeling

Human microbiota communicates with its host by secreting signaling metabolites, enzymes, or structural components. Its homeostasis strongly influences the modulation of human tissue barriers and immune system. Dysbiosis-induced peripheral immunity response can propagate bacterial and pro-inflammatory signals to the whole body, including the brain. This immune-mediated communication may contribute to several neurodegenerative disorders, as Alzheimer's disease. In fact, neurodegeneration is associated with dysbiosis and neuroinflammation. The interplay between the microbial communities and the brain is complex and bidirectional, and a great deal of interest is emerging to define the exact mechanisms. This review focuses on microbiota-immunity-central nervous system (CNS) communication and shows how gut and oral microbiota populations trigger immune cells, propagating inflammation from the periphery to the cerebral parenchyma, thus contributing to the onset and progression of neurodegeneration. Moreover, an overview of the technological challenges with in vitro modeling of the microbiota-immunity-CNS axis, offering interesting technological hints about the most advanced solutions and current technologies is provided.

Increased tortuosity of bilateral distal internal carotid artery is associated with white matter hyperintensities

BACKGROUND

Although the pathophysiology of white matter hyperintensities remains unclear, we can recently explore the possible relationship with white matter hyperintensities by using quantitative parameter.

PURPOSE

To demonstrate the relationship between bilateral distal internal carotid arterial tortuosity and total brain white matter hyperintensities volume in elderly individuals.

MATERIAL AND METHODS

A total of 345 patients (age > 65 years) with brain magnetic resonance (MR) examinations were retrospectively included (44.1% men; mean age = 72.1 ± 6.25 years; 55.9% ≥ 70 years). We measured the Tortuosity Index (TI) of the bilateral distal internal carotid artery and basilar artery on MR angiography imaging, and white matter hyperintensities volume on fluid-attenuated inversion recovery MR sequence. Multiple linear regression was used to assess the association of the TI with quantitatively derived brain white matter hyperintensity volume, after adjusting for demographics (age, sex), vascular risk factors (hypertension, diabetes, heart disease), and vessel diameters, total intracranial volume (TIV).

RESULTS

Increased tortuosity of bilateral distal internal carotid artery was associated with greater burden of white matter hyperintensity volume (right: β = 11.223, P = 0.016; left: β = 20.701, P < 0.001). This relationship was independent of age and hypertension, both of which have been considered the strongest risk factors for white matter hyperintensities.

CONCLUSION

Our results suggest that tortuosity of the bilateral distal internal carotid artery is associated with white matter hyperintensities, independent of age and hypertension.

Hemodynamic Changes in an Actively Rupturing Abdominal Aortic Aneurysm

Computational fluid dynamics were used to assess hemodynamic changes in an actively rupturing abdominal aortic aneurysm (AAA) over a 9-day period. Active migration of contrast from the lumen into the thickest region of intraluminal thrombus (ILT) was demonstrated until it ultimately breached the adventitial layer. Four days after symptom onset, there was a discrete disruption of adventitial calcium with bleb formation at the site of future rupture. Rupture occurred in a region of low wall shear stress and was associated with a marked increase in AAA diameter from 6.6 to 8.4 cm. The cross-sectional area of the flow lumen increased across all time points from 6.28 to 12.08 cm2. The increase in luminal area preceded the increase in AAA diameter and was characterized by an overall deceleration in recirculation flow velocity with a coinciding increase in flow velocity penetrating the ILT. We show that there are significant hemodynamic and structural changes in the AAA flow lumen in advance of any appreciable increase in aortic diameter or rupture. The significant increase in AAA diameter with rupture suggests that AAA may actually rupture at smaller sizes than those measured on day of rupture. These findings have implications for algorithms the predict AAA rupture risk.

Case Report: Evaluating Biomechanical Risk Factors in Carotid Stenosis by Patient-Specific Fluid-Structural Interaction Biomechanical Analysis

BACKGROUND

Carotid atherosclerosis is one of the main underlying inducements of stroke, which is a leading cause of disability. The morphological feature and biomechanical environment have been found to play important roles in atherosclerotic plaque progression. However, the biomechanics in each patient's blood vessel is complicated and unique.

METHOD

To analyse the biomechanical risk of the patient-specific carotid stenosis, this study used the fluid-structure interaction (FSI) computational biomechanical model. This model coupled both structural and hemodynamic analysis. Two patients with carotid stenosis planned for carotid endarterectomy were included in this study. The 3D models of carotid bifurcation were reconstructed using our in-house-developed protocol based on multisequence magnetic resonance imaging (MRI) data. Patient-specific flow and pressure waveforms were used in the computational analysis. Multiple biomechanical risk factors including structural and hemodynamic stresses were employed in post-processing to assess the plaque vulnerability.

RESULTS

Significant difference in morphological and biomechanical conditions between 2 patients was observed. Patient I had a large lipid core and serve stenosis at carotid bulb. The stenosis changed the cross-sectional shape of the lumen. The blood flow pattern changed consequently and led to a complex biomechanical environment. The FSI results suggested a potential plaque progression may lead to a high-risk plaque, if no proper treatment was performed. The patient II had significant tandem stenosis at both common and internal carotid artery (CCA and ICA). From the results of biomechanical factors, both stenoses had a high potential of plaque progression. Especially for the plaque at ICA branch, the current 2 small plaques might further enlarge and merge as a large vulnerable plaque. The risk of plaque rupture would also increase.

CONCLUSIONS

Computational biomechanical analysis is a useful tool to provide the biomechanical risk factors to help clinicians assess and predict the patient-specific plaque vulnerability. The FSI computational model coupling the structural and hemodynamic computational analysis, better replicates the in vivo biomechanical condition, which can provide multiple structural and flow-based risk factors to assess plaque vulnerability.

Vessel Enlargement in Development and Pathophysiology

From developmental stages until adulthood, the circulatory system remodels in response to changes in blood flow in order to maintain vascular homeostasis. Remodeling processes can be driven by de novo formation of vessels or angiogenesis, and by the restructuration of already existing vessels, such as vessel enlargement and regression. Notably, vessel enlargement can occur as fast as in few hours in response to changes in flow and pressure. The high plasticity and responsiveness of blood vessels rely on endothelial cells. Changes within the bloodstream, such as increasing shear stress in a narrowing vessel or lowering blood flow in redundant vessels, are sensed by endothelial cells and activate downstream signaling cascades, promoting behavioral changes in the involved cells. This way, endothelial cells can reorganize themselves to restore normal circulation levels within the vessel. However, the dysregulation of such processes can entail severe pathological circumstances with disturbances affecting diverse organs, such as human hereditary telangiectasias. There are different pathways through which endothelial cells react to promote vessel enlargement and mechanisms may differ depending on whether remodeling occurs in the adult or in developmental models. Understanding the molecular mechanisms involved in the fast-adapting processes governing vessel enlargement can open the door to a new set of therapeutical approaches to be applied in occlusive vascular diseases. Therefore, we have outlined here the latest advances in the study of vessel enlargement in physiology and pathology, with a special insight in the pathways involved in its regulation.

Endogenous animal models of intracranial aneurysm development: a review

The pathogenesis and natural history of intracranial aneurysm (IA) remains poorly understood. To this end, animal models with induced cerebral vessel lesions mimicking human aneurysms have provided the ability to greatly expand our understanding. In this review, we comprehensively searched the published literature to identify studies that endogenously induced IA formation in animals. Studies that constructed aneurysms (i.e., by surgically creating a sac) were excluded. From the eligible studies, we reported information including the animal species, method for aneurysm induction, aneurysm definitions, evaluation methods, aneurysm characteristics, formation rate, rupture rate, and time course. Between 1960 and 2019, 174 articles reported endogenous animal models of IA. The majority used flow modification, hypertension, and vessel wall weakening (i.e., elastase treatment) to induce IAs, primarily in rats and mice. Most studies utilized subjective or qualitative descriptions to define experimental aneurysms and histology to study them. In general, experimental IAs resembled the pathobiology of the human disease in terms of internal elastic lamina loss, medial layer degradation, and inflammatory cell infiltration. After the early 2000s, many endogenous animal models of IA began to incorporate state-of-the-art technology, such as gene expression profiling and 9.4-T magnetic resonance imaging (MRI) in vivo imaging, to quantitatively analyze the biological mechanisms of IA. Future studies aimed at longitudinally assessing IA pathobiology in models that incorporate aneurysm growth will likely have the largest impact on our understanding of the disease. We believe this will be aided by high-resolution, small animal, survival imaging, in situ live-cell imaging, and next-generation omics technology.

Modeling flow in embryonic lymphatic vasculature: what is its role in valve development?

A majority of lymphatic valves tend to form in proximity to vessel junctions, and it is often proposed that disturbed flow at junctions creates oscillating shear stress that leads to accumulation of transcription factors which bring about valvogenesis at these sites. In images of networks of dorsal skin lymphatics from embryonic mice (day E16), we compared simulated fluid flow patterns and observed distributions of the transcription factor Prox1, which is implicated in valve formation. Because of creeping-flow conditions, flow across vessel junctions was not 'disturbed', and within a given vessel, shear stress varied inversely with local conduit width. Prox1 concentration was indeed localised to vessel end-regions, but over three networks was not consistently correlated with the vessel normalised-distance distribution of either fluid shear stress or shear-stress axial gradient. These findings do not support the presently accepted mechanism for the role of flow in valve localisation.

Quantification of Oscillatory Shear Stress from Reciprocating CSF Motion on 4D Flow Imaging

BACKGROUND AND PURPOSE

Oscillatory shear stress could not be directly measured in consideration of direction, although cerebrospinal fluid has repetitive movements synchronized with heartbeat. Our aim was to evaluate the important of oscillatory shear stress in the cerebral aqueduct and foramen magnum in idiopathic normal pressure hydrocephalus by comparing it with wall shear stress and the oscillatory shear index in patients with idiopathic normal pressure hydrocephalus.

MATERIALS AND METHODS

By means of the 4D flow application, oscillatory shear stress, wall shear stress, and the oscillatory shear index were measured in 41 patients with idiopathic normal pressure hydrocephalus, 23 with co-occurrence of idiopathic normal pressure hydrocephalus and Alzheimer-type dementia, and 9 age-matched controls. These shear stress parameters at the cerebral aqueduct were compared with apertures and stroke volumes at the foramen of Magendie and cerebral aqueduct.

RESULTS

Two wall shear stress magnitude peaks during a heartbeat were changed to periodic oscillation by converting oscillatory shear stress. The mean oscillatory shear stress amplitude and time-averaged wall shear stress values at the dorsal and ventral regions of the cerebral aqueduct in the idiopathic normal pressure hydrocephalus groups were significantly higher than those in controls. Furthermore, those at the ventral region of the cerebral aqueduct in the idiopathic normal pressure hydrocephalus group were also significantly higher than those in the co-occurrence of idiopathic normal pressure hydrocephalus with Alzheimer-type dementia group. The oscillatory shear stress amplitude at the dorsal region of the cerebral aqueduct was significantly associated with foramen of Magendie diameters, whereas it was strongly associated with the stroke volume at the upper end of the cerebral aqueduct rather than that at the foramen of Magendie.

CONCLUSIONS

Oscillatory shear stress, which reflects wall shear stress vector changes better than the conventional wall shear stress magnitude and the oscillatory shear index, can be directly measured on 4D flow MR imaging. Oscillatory shear stress at the cerebral aqueduct was considerably higher in patients with idiopathic normal pressure hydrocephalus.

A scoring system to discriminate blood blister-like aneurysms: a multidimensional study using patient-specific model

Presurgical discrimination of blood blister-like aneurysms (BBAs) can assist neurosurgeons in clinical decision-making. The aim of this study was to investigate the characteristics of BBAs and construct a useful tool to distinguish BBAs. This study reviewed patients with small/median, hemispherical, and wide-necked aneurysms of the internal carotid artery in our institution. BBAs were identified via their intraoperative findings. A hemodynamic analysis was performed using a patient-specific model. The independent risk factors of BBAs were investigated using a logistic analysis. A scoring system was then established to discriminate BBAs, in which its predicting value was analyzed using receiver operating characteristic (ROC) analysis. A total of 67 aneurysms comprising 21 BBAs were enrolled. Comparing features between BBAs and non-BBAs, statistical significances were found in the aspect ratio (AR), height-to-width ratio, aneurysm angle (AA), wall shear stress gradient (WSSG), and normalized wall shear stress average. A multivariate logistic analysis identified AR (OR = 0.29, p = 0.021), WSSG (OR = 1.54, p = 0.017) and AA (OR = 2.49, p = 0.039) as independent risk factors for BBAs. A scoring system was constructed using these parameters, effectively distinguishing BBAs (AUC = 0.931, p < 0.01). Our multidimensional scoring system may effectively assist in the discrimination of BBAs from wide-necked non-BBAs.

Endothelial Cells Morphology in Response to Combined WSS and Biaxial CS: Introduction of Effective Strain Ratio

Introduction

Endothelial cells (ECs) morphology strongly depends on the imposed mechanical stimuli. These mechanical stimuli include wall shear stress (WSS) and biaxial cyclic stretches (CS). Under combined loading, the effect of CS is not as simple as pure CS. The present study investigates the morphological response of ECs to the realistic mechanical stimuli.

Methods

The cell population is theoretically studied using our previous validated model. The mechanical stimuli on ECs are described using four parameters; WSS magnitude (0 to 2.0 Pa), WSS angle (- 50° to 50°), and biaxial CS in two perpendicular directions (0 to 10%). The morphology of ECs is reported using four parameters; average shape index (SI) and orientation angle (OA) of the cell population as well as the standard deviation (SD) of SI and OA as measures for scattering of cells' SI and OA from these average values.

Results

A new effective strain ratio (ESR) is defined as the ratio of the undesirable CS to the desirable one. The obtained results of the model, illustrated that the SI and OA of cells increase with absolute value of ESR. In addition, the scattering in the SI of cells decreases with the absolute value of ESR, which means that the cell shapes become more regular. It is shown that the angular irregularity of cells increases at higher ESR values.

Conclusions

The results indicated that, the defined ESR is a stand-alone parameter for describing the realistic mechanical loading on the ECs and their morphological response.

Endothelial cell polarization and orientation to flow in a novel microfluidic multimodal shear stress generator

Endothelial cells (EC) respond to shear stress to maintain vascular homeostasis, and a disrupted response is associated with cardiovascular diseases. To understand how different shear stress modalities affect EC morphology and behavior, we developed a microfluidic device that concurrently generates three different levels of uniform wall shear stress (WSS) and six different WSS gradients (WSSG). In this device, human umbilical vein endothelial cells (HUVECs) exhibited a rapid and robust response to WSS, with the relative positioning of the Golgi and nucleus transitioning from a non-polarized to polarized state in a WSS magnitude- and gradient-dependent manner. By contrast, polarized HUVECs oriented their Golgi and nucleus polarity to the flow vector in a WSS magnitude-dependent manner, with positive WSSG inhibiting and negative WSSG promoting upstream orientation. Having validated this device, this chip can now be used to dissect the mechanisms underlying EC responses to different WSS modalities, including shear stress gradients, and to investigate the influence of flow on a diverse range of cells during development, homeostasis and disease.

Circulating products of C-type natriuretic peptide and links with organ function in health and disease

Paracrine actions of CNP and rapid degradation at source severely limit study of CNP's many roles in vivo. However provided sensitive and validated assays are used, there is increasing evidence that low concentrations of bioactive CNP in plasma, and the readily detectable concentrations of the bio-inactive processed product of proCNP (aminoterminal proCNP), can be used to advance understanding of the hormone's role in pathophysiology. Provided renal function is normal, concordant changes in both CNP and NTproCNP reflect change in tissue production of proCNP whereas change in CNP alone results from altered rates of bioactive CNP degradation and are reflected in the ratio of NTproCNP to CNP. As already shown in juveniles, where plasma concentration of CNP products are higher and are associated with concurrent endochondral bone growth, measurements of plasma CNP products in mature adults have potential to clarify organ response to stress and injury. Excepting the role of CNP in fetal-maternal welfare, this review examines evidence linking plasma CNP products with function of a wide range of tissues in adults, including the impact of extraneous factors such as nutrients, hormone therapy and exercise.

Blood flow simulations in patient-specific geometries of the carotid artery: A systematic review

Computational Fluid Dynamics (CFD) and Fluid-Structure Interaction (FSI) are currently widely applied in the study of blood flow parameters and their alterations under pathological conditions, which are important indicators for diagnosis of atherosclerosis. In this manuscript, a systematic review of the published literature was conducted, according to the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses, on the simulation studies of blood flow in patient-specific geometries of the carotid artery bifurcation. Scopus, PubMed and ScienceDirect databases were used in the literature search, which was completed on the 3rd of August 2020. Forty-nine articles were included after the selection process and were organized in two distinct categories: the CFD studies (36/49 articles), which comprise only the fluid analysis and the FSI studies (13/49 articles), which includes both fluid and Fluid-Structure domain in the analysis. The data of the research works was structured in different categories (Geometry, Viscosity models, Type of Flow, Boundary Conditions, Flow Parameters, Type of Solver and Validation). The aim of this systematic review is to demonstrate the methodology in the modelling, simulation and analysis of carotid blood flow and also identify potential gaps and challenges in this research field.

Patient-Specific Numerical Analysis of Coronary Flow in Children With Intramural Anomalous Aortic Origin of Coronary Arteries

Unroofing surgery for anomalous aortic origin of a coronary artery (AAOCA) alters coronary anatomy by opening the intramural segment so that the anomalous coronary orifice arises perpendicularly from appropriate aortic sinus. Computational fluid dynamics modeling (CFD) allows for quantification of hemodynamics linked to morbidity such as wall shear stress (WSS), relative to patient-specific features like the angle of origin (AO). We hypothesize that CFD will reveal abnormal WSS indices in unroofed arteries that are related to AO. Six AAOCA patients (3 left, 3 right) status post unroofing (median = 13.5 years, range 9-17) underwent cardiac magnetic resonance imaging. CFD models were created from pre (n = 2) and postunroofing (n = 6) cardiac magnetic resonance imaging data, for the anomalous and contralateral normally-arising arteries. Downstream vasculature was represented by lumped parameter networks. Time-averaged WSS (TAWSS) and oscillatory shear index (OSI) were quantified relative to AO and measured hemodynamics. TAWSS was elevated along the outer wall of the normally-arising left vs right coronary arteries, as well as along unroofed left vs right coronary arteries (n = 6/group). No significant differences were noted when comparing unroofed and same-sided normally-arising coronaries. TAWSS was reduced after unroofing (eg, 276 ± 28 dyne/cm² vs 91 ± 15 dyne/cm²; n = 2/group). Models with more acute preoperative AO indicated lower TAWSS at the proximity of ostium. Differences in OSI were not significant. Different flow patterns exist natively between right and left coronary arteries. Unroofing may normalize TAWSS but with variance related to the AO. This study suggests CFD may help stratify risk in AAOCA.

Flow-induced, inflammation-mediated arterial wall remodeling in the formation and progression of intracranial aneurysms

OBJECTIVE

Unruptured intracranial aneurysms (UIAs) are relatively common lesions that may cause devastating intracranial hemorrhage, thus producing considerable suffering and anxiety in those affected by the disease or an increased likelihood of developing it. Advances in the knowledge of the pathobiology behind intracranial aneurysm (IA) formation, progression, and rupture have led to preclinical testing of drug therapies that would prevent IA formation or progression. In parallel, novel biologically based diagnostic tools to estimate rupture risk are approaching clinical use. Arterial wall remodeling, triggered by flow and intramural stresses and mediated by inflammation, is relevant to both.

METHODS

This review discusses the basis of flow-driven vessel remodeling and translates that knowledge to the observations made on the mechanisms of IA initiation and progression on studies using animal models of induced IA formation, study of human IA tissue samples, and study of patient-derived computational fluid dynamics models.

RESULTS

Blood flow conditions leading to high wall shear stress (WSS) activate proinflammatory signaling in endothelial cells that recruits macrophages to the site exposed to high WSS, especially through macrophage chemoattractant protein 1 (MCP1). This macrophage infiltration leads to protease expression, which disrupts the internal elastic lamina and collagen matrix, leading to focal outward bulging of the wall and IA initiation. For the IA to grow, collagen remodeling and smooth muscle cell (SMC) proliferation are essential, because the fact that collagen does not distend much prevents the passive dilation of a focal weakness to a sizable IA. Chronic macrophage infiltration of the IA wall promotes this SMC-mediated growth and is a potential target for drug therapy. Once the IA wall grows, it is subjected to changes in wall tension and flow conditions as a result of the change in geometry and has to remodel accordingly to avoid rupture. Flow affects this remodeling process.

CONCLUSIONS

Flow triggers an inflammatory reaction that predisposes the arterial wall to IA initiation and growth and affects the associated remodeling of the UIA wall. This chronic inflammation is a putative target for drug therapy that would stabilize UIAs or prevent UIA formation. Moreover, once this coupling between IA wall remodeling and flow is understood, data from patient-specific flow models can be gathered as part of the diagnostic workup and utilized to improve risk assessment for UIA initiation, progression, and eventual rupture.

The biophysical role of hemodynamics in the pathogenesis of cerebral aneurysm formation and rupture

The pathogenesis of intracranial aneurysms remains complex and multifactorial. While vascular, genetic, and epidemiological factors play a role, nascent aneurysm formation is believed to be induced by hemodynamic forces. Hemodynamic stresses and vascular insults lead to additional aneurysm and vessel remodeling. Advanced imaging techniques allow us to better define the roles of aneurysm and vessel morphology and hemodynamic parameters, such as wall shear stress, oscillatory shear index, and patterns of flow on aneurysm formation, growth, and rupture. While a complete understanding of the interplay between these hemodynamic variables remains elusive, the authors review the efforts that have been made over the past several decades in an attempt to elucidate the physical and biological interactions that govern aneurysm pathophysiology. Furthermore, the current clinical utility of hemodynamics in predicting aneurysm rupture is discussed.

An image-based computational hemodynamics study of the Systolic Anterior Motion of the mitral valve

Systolic Anterior Motion (SAM) of the mitral valve - often associated with Hypertrophic Obstructive Cardiomyopathy (HOCM) - is a cardiac pathology in which a functional subaortic stenosis is induced during systole by the mitral leaflets partially obstructing the outflow tract of the left ventricle. Its assessment by diagnostic tests is often difficult, possibly underestimating its severity and thus increasing the risk of heart failure. In this paper, we propose a new computational pipeline, based on cardiac cine Magnetic Resonance Imaging (cine-MRI) data, for the assessment of SAM. The pipeline encompasses image processing of the left ventricle and the mitral valve, and numerical investigation of cardiac hemodynamics by means of Computational Fluid Dynamics (CFD) in a moving domain with image-based prescribed displacement. Patient-specific geometry and motion of the left ventricle are considered in view of an Arbitrary Lagrangian-Eulerian approach for CFD, while the reconstructed mitral valve is immersed in the computational domain by means of a resistive method. We assess clinically relevant flow and pressure indicators in a parametric study for different degrees of SAM severity, in order to provide a better quantitative evaluation of the pathological condition. Moreover, we provide specific indications for its possible surgical treatment, i.e. septal myectomy.

Dysregulated long non-coding RNAs involved in regulation of matrix degradation during type-B aortic dissection pathogenesis

Thoracic aortic dissection (TAD) is a catastrophic disease with the rupture of aortic media resulted mainly from the degradation of extracellular matrix. With the deep study of long non-coding RNAs (lncRNAs) in cardiovascular diseases, the correlation between lncRNAs and the TAD pathogenesis is under revealed. In this study, we aimed to screen the differentially expressed lncRNAs involved in the regulation of matrix degradation during type-B aortic dissection (TBAD), whose pathogenesis is more similar to atherosclerosis. A total of 393 aberrantly expressed lncRNAs and 432 aberrantly expressed mRNAs were identified in the descending aortic samples from TBAD patients. Then, co-expression analysis was applied to analyze the correlation between the top five differentially expressed lncRNAs and aberrantly expressed mRNAs, so as to screen the lncRNAs involved in the regulation of matrix degradation. The results showed that two transcripts from lnc-TNFSF14 (lnc-TNFSF14-2, and lnc-TNFSF14-3) were negatively interacted with MMP14 and MMP19. Subsequently, quantitative real-time PCR assay confirmed that lnc-TNFSF14-2 were negatively correlated with MMP14 (r_s = - 0.8180) and MMP19 (r_s = - 0.8449), and lnc-TNFSF14-3 was also negatively correlated with MMP14 (r_s = - 0.7098) and MMP19 (r_s = - 0.7728) in descending aorta from TBAD patients (n = 20). Overall, our study found the aberrant lncRNAs expression profiles in TBAD, and identified lnc-TNFSF14 as a potential target regulating matrix degradation. The results also provided crucial clues for lncRNAs function research on TBAD development.

Role of Morphological and Hemodynamic Factors in Predicting Intracranial Aneurysm Rupture: A Review

Intracranial aneurysms (IAs) carry the risk of rupture, which will lead to subarachnoid hemorrhage, which has a high mortality and morbidity risk. However, the treatment of IA's carries mortality and morbidity risks too. There are well-known risk factors for the rupture of IAs like age, size, and site. However, choosing patients with unruptured IAs for treatment is still a big challenge. This review article aimed to find out the relationship between morphological and hemodynamic characters of IAs with their rupture and incorporate these factors with well-known factors to yield an accurate module for predicting the rupture of IAs and decision-making in the treatment of unruptured IAs.

We searched in PubMed and Medline databases by using the following keywords: IAs, subarachnoid hemorrhage, and risk of rupture, morphology, and hemodynamic “mesh.” A total of 19 studies with 7269 patients and 9167 IAs, of which 1701 had ruptured, were reviewed thoroughly. Some modules like population, hypertension, age, size, earlier subarachnoid hemorrhage, and site (PHASES) score that involve well-known risk factors can be used to assess the risk of rupture of IAs. However, decision making for treating unruptured IA needs more detailed and more accurate modules. Studying morphological and hemodynamic factors and incorporation of them with well-known risk factors to yield a more comprehensive module will be very helpful in treating unruptured IA. Among morphological factors, aspect ratio (AR), size ratio (SR), aneurysm height, and bottle-neck factor showed significant effects on the growth and rupture of IA. Besides, wall shear stress (WSS), oscillatory shear index (OSI), and low wall shear stress area (LSA) as hemodynamic factors could have a substantial impact on the formation, shape, growth, and rupture of unruptured IA.

[Analysis of local hemodynamics in complex aneurysms: an effect of the vessel arising from the dome or the neck]

BACKGROUND

Assessment of rupture risk for intracranial aneurysms (IA) is a particular challenge in cases of so-called complex aneurysms due to their variable morphometric characteristics. Arterial branch arising from the dome or the neck of IA is one of the least explored features of complex aneurysms. The methods of computational fluid dynamics may be valuable to determine the influence of arterial branches of IA on local hemodynamics.

OBJECTIVE

To analyze local hemodynamics in IA with arterial branch arising from the cupola or the neck depending on the structure of the aneurysm and blood flow rate in the parent vessel.

MATERIAL AND METHODS

CT angiography data of 4 patients with IA were estimated in this study. Modifications of the baseline 3D models of the aneurysms resulted 12 patient-specific models included into analysis. Hemodynamic calculations were made by using of ANSYS Workbench 19 software package.

RESULTS

Wall shear stress (WSS) was characterized by the most significant variability, especially in case of sidewall aneurysms. Small cross-sectional area of additional branch in relation to the neck of IA was not followed by considerable changes of blood flow patterns inside IA after «virtual» removal of the vessel. Otherwise, the intensity of flows was drastically reduced. Simulation of high inlet flows demonstrated substantial variation of WSS in the area of jet.

CONCLUSION

Additional arterial branch arising from the dome or the neck of IA significantly influences local hemodynamics. This influence depends on the localization of IA in relation to the parent vessel and the diameter of additional arterial branch.

Coronary arteries hemodynamics: effect of arterial geometry on hemodynamic parameters causing atherosclerosis

Coronary arteries have high curvatures, and hence, flow through them causes disturbed flow patterns, resulting in stenosis and atherosclerosis. This in turn decreases the myocardial flow perfusion, causing myocardial ischemia and infarction. Therefore, in order to understand the mechanisms of these phenomena caused by high curvatures and branching of coronary arteries, we have conducted elaborate hemodynamic analysis for both (i) idealized coronary arteries with geometrical parameters representing realistic curvatures and stenosis and (ii) patient-specific coronary arteries with stenoses. Firstly, in idealized coronary arteries with approximated realistic arterial geometry representative of their curvedness and stenosis, we have computed the hemodynamic parameters of pressure drop, wall shear stress (WSS) and wall pressure gradient (WPG), and their association with the geometrical parameters of curvedness and stenosis. Secondly, we have similarly determined the wall shear stress and wall pressure gradient distributions in four patient-specific curved stenotic right coronary arteries (RCAs), which were reconstructed from medical images of patients diagnosed with atherosclerosis and stenosis; our results show high WSS and WPG regions at the stenoses and inner wall of the arterial curves. This paper provides useful insights into the causative mechanisms of the high incidence of atherosclerosis in coronary arteries. It also provides guidelines for how simulation of blood flow in patient's coronary arteries and determination of the hemodynamic parameters of WSS and WPG can provide a medical assessment of the risk of development of atherosclerosis and plaque formation, leading to myocardial ischemia and infarction. The novelty of our paper is in our showing how in actual coronary arteries (based on their CT imaging) curvilinearity and narrowing complications affect the computed WSS and WPG, associated with risk of atherosclerosis. This is very important for cardiologists to be able to properly take care of their patients and provide remedial measures before coronary complications lead to myocardial infarctions and necessitate stenting or coronary bypass surgery. We want to go one step further and provide clinical application of our research work. For that, we are offering to cardiologists worldwide to carry out hemodynamic analysis of the medically imaged coronary arteries of their patients and compute the values of the hemodynamic parameters of WSS and WPG, so as to provide them an assessment of the risk of atherosclerosis for their patients. Graphical abstract Theme and aims: Coronary arteries have high curvatures, and hence flow through them causes disturbed flow patterns, resulting in stenosis and atherosclerosis. This in turn decreases the myocardial flow perfusion, causing myocardial ischemia and infarction. Therefore, in order to understand the mechanisms of these phenomena caused by high curvatures and branching of coronary arteries, we have conducted elaborate hemodynamic analysis for both (i) idealized coronary arteries with geometrical parameters representing curvatures and stenosis, and (ii) patient-specific coronary arteries with stenoses. Methods and results: Firstly, in idealized coronary arteries with approximated realistic arterial geometry representative of their curvedness and stenosis, we have computed the hemodynamic parameters of pressure drop, wall shear stress (WSS) and wall pressure gradient (WPG), and their association with the geometrical parameters of curvedness and stenosis. Then, we have determined the wall shear stress and wall pressure gradient distributions in four patient-specific curved stenotic right coronary arteries (RCAs), that were reconstructed from medical images of patients diagnosed with atherosclerosis and stenosis, as illustrated in Figure 1, in which the locations of the stenoses are highlighted by arrows. Figure 1: Three-dimensional CT visualization of arteries in patients with suspected coronary disease. The arteries can be seen as a combination of various curved segments with stenoses at unspecific locations highlighted by arrows. Our results show high WSS and WPG regions at the stenoses and inner wall of the arterial curves, as depicted in Figure 2. Therein, the encapsulations show (i) high WSS, and (ii) high WPG regions at the stenosis and inner wall of the arterial curves. Figure 2: WSS and WPG surface plot of realistic arteries (a), (b), (c) and (d), wherein the small squared parts are enlarged to show the detailed localized contour plots at the stenotic regions. Therein, the circular encapsulations show (i) high WSS and (ii) high WPG regions at the stenosis and inner wall of the arterial curves. Conclusion and novelty: This paper provides useful insights into the causative mechanisms of the high incidence of atherosclerosis in coronary arteries. It also provides guidelines for how simulation of blood flow in patient coronary arteries and determination of the hemodynamic parameters of WSS and WPG can provide a medical assessment of the risk of development of atherosclerosis and plaque formation, leading to myocardial ischemia and infarction. The novelty of our paper is our showing how in actual coronary arteries (based on their CT imaging), curvilinearity and narrowing complications affect the computed WSS and WPG associated with risk of atherosclerosis. This is very important for cardiologists to be able to properly take care of their patients and provide remedial measures before coronary complications lead to myocardial infarctions and necessitate stenting or coronary bypass surgery.

Increased focal internal carotid artery angulation in patients with posterior communicating artery aneurysms

Background

Aneurysms at the posterior communicating artery (PCOM) origin represent the most common location on the internal carotid artery (ICA), and are associated with greater recurrence following endovascular treatment. We evaluate the association between ICA angulation in three-dimensional (3D) space and PCOM aneurysmal development, using high-resolution 3D rotational angiography (3DRA) studies.

Methods

3DRA datasets were evaluated in 70 patients with PCOM aneurysms, 31 non-aneurysmal contralateral, and 86 healthy controls (187 total). The local angle formed by upstream and downstream ICA segments at the PCOM origin, αICA@PCOM, was measured using 3DRA multiplanar reconstruction. Computational fluid dynamics (CFD) analysis was performed on parametric and patient-based models.

Results

αICA@PCOM was significantly larger in aneurysm-bearing ICA segments (68.14±11.91°) compared with non-aneurysmal contralateral (57.17±10.76°, p<0.001) and healthy controls (48.13±13.68°, p<0.001). A discriminant threshold αICA@PCOM value of 61° (87% specificity, 80% sensitivity) was established (area under the curve (AUC)=0.88). Ruptured PCOM aneurysms had a significantly larger αICA@PCOM compared to unruptured (72.65±15.16° vs 66.35±9.94°, p=0.04). In parametric and patient-based CFD analysis, a large αICA@PCOM induces high focal pressure at the PCOM origin, relatively low wall shear stress (WSS), and high proximal WSS spatial gradients (WSSG).

Conclusion

ICA angulation at PCOM origin is significantly higher in vessels harboring PCOM aneurysms compared with contralateral and healthy ICAs. This sharper bend in the ICA leads to high focal pressure at the aneurysm neck, low focal WSS and high proximal WSSG. These findings underline the importance of morphological ICA variations and the likelihood of PCOM aneurysm, an association which can inform clinical decisions and may serve in predictive analytics.

Dedifferentiation of smooth muscle cells in intracranial aneurysms and its potential contribution to the pathogenesis

Smooth muscle cells (SMCs) are the major type of cells constituting arterial walls and play a role to maintain stiffness via producing extracellular matrix. Here, the loss and degenerative changes of SMCs become the major histopathological features of an intracranial aneurysm (IA), a major cause of subarachnoid hemorrhage. Considering the important role of SMCs and the loss of this type of cells in IA lesions, we in the present study subjected rats to IA models and examined how SMCs behave during disease progression. We found that, at the neck portion of IAs, SMCs accumulated underneath the internal elastic lamina according to disease progression and formed the intimal hyperplasia. As these SMCs were positive for a dedifferentiation marker, myosin heavy chain 10, and contained abundant mitochondria and rough endoplasmic reticulum, SMCs at the intimal hyperplasia were dedifferentiated and activated. Furthermore, dedifferentiated SMCs expressed some pro-inflammatory factors, suggesting the role in the formation of inflammatory microenvironment to promote the disease. Intriguingly, some SMCs at the intimal hyperplasia were positive for CD68 and contained lipid depositions, indicating similarity with atherosclerosis. We next examined a potential factor mediating dedifferentiation and recruitment of SMCs. Platelet derived growth factor (PDGF)-BB was expressed in endothelial cells at the neck portion of lesions where high wall shear stress (WSS) was loaded. PDGF-BB facilitated migration of SMCs across matrigel-coated pores in a transwell system, promoted dedifferentiation of SMCs and induced expression of pro-inflammatory genes in these cells in vitro. Because, in a stenosis model of rats, PDGF-BB expression was expressed in endothelial cells loaded in high WSS regions, and SMCs present nearby were dedifferentiated, hence a correlation existed between high WSS, PDGFB and dedifferentiation in vivo. In conclusion, dedifferentiated SMCs presumably by PDGF-BB produced from high WSS-loaded endothelial cells accumulate in the intimal hyperplasia to form inflammatory microenvironment leading to the progression of the disease.

What does computational fluid dynamics tell us about intracranial aneurysms? A meta-analysis and critical review

Despite the plethora of published studies on intracranial aneurysms (IAs) hemodynamic using computational fluid dynamics (CFD), limited progress has been made towards understanding the complex physics and biology underlying IA pathophysiology. Guided by 1733 published papers, we review and discuss the contemporary IA hemodynamics paradigm established through two decades of IA CFD simulations. We have traced the historical origins of simplified CFD models which impede the progress of comprehending IA pathology. We also delve into the debate concerning the Newtonian fluid assumption used to represent blood flow computationally. We evidently demonstrate that the Newtonian assumption, used in almost 90% of studies, might be insufficient to describe IA hemodynamics. In addition, some fundamental properties of the Navier-Stokes equation are revisited in supplementary material to highlight some widely spread misconceptions regarding wall shear stress (WSS) and its derivatives. Conclusively, our study draws a roadmap for next-generation IA CFD models to help researchers investigate the pathophysiology of IAs.

Targeting functionalized nanoparticles to activated endothelial cells under high wall shear stress

Local inflammation of the endothelium is associated with a plethora of cardiovascular diseases. Vascular-targeted carriers (VTCs) have been advocated to provide focal effective therapeutics to these disease sites. Here, we examine the design of functionalized nanoparticles (NPs) as VTCs that can specifically localize at an inflamed vessel wall under pathological levels of high shear stress, associated for example with clinical (or in vivo) conditions of vascular narrowing and arteriogenesis. To test this, carboxylated fluorescent 200 nm polystyrene particles were functionalized with ligands to activated endothelium, that is, an E-selectin binding peptide (Esbp), an anti ICAM-1 antibody, or using a combination of both. The functionalized NPs were investigated in vitro using microfluidic models lined with inflamed (TNF-α stimulated) and control endothelial cells (EC). Specifically, their adhesion was monitored under different relevant wall shear stresses (i.e., 40-300 dyne/cm2) via real-time confocal microscopy. Experiments reveal a significantly higher specific adhesion of the examined functionalized NPs to activated EC for the window of examined wall shear stresses. Moreover, particle adhesion correlated with the surface coating density whereby under high surface coating (i.e., ~10,000 molecule/particle), shear-dependent particle adhesion increased significantly. Altogether, our results show that functionalized NPs can be designed to target inflamed endothelial cells under high shear stress. Such VTCs underscore the potential for attractive avenues in targeting drugs to vasoconstriction and arteriogenesis sites.

Hemodynamics of Cerebral Aneurysms: Connecting Medical Imaging and Biomechanical Analysis

In the last two decades, numerous studies have conducted patient-specific computations of blood flow dynamics in cerebral aneurysms and reported correlations between various hemodynamic metrics and aneurysmal disease progression or treatment outcomes. Nevertheless, intra-aneurysmal flow analysis has not been adopted in current clinical practice, and hemodynamic factors usually are not considered in clinical decision making. This review presents the state of the art in cerebral aneurysm imaging and image-based modeling, discussing the advantages and limitations of each approach and focusing on the translational value of hemodynamic analysis. Combining imaging and modeling data obtained from different flow modalities can improve the accuracy and fidelity of resulting velocity fields and flow-derived factors that are thought to affect aneurysmal disease progression. It is expected that predictive models utilizing hemodynamic factors in combination with patient medical history and morphological data will outperform current risk scores and treatment guidelines. Possible future directions include novel approaches enabling data assimilation and multimodality analysis of cerebral aneurysm hemodynamics.

The hydromechanics in arteriogenesis

Coronary heart diseases are tightly associated with aging. Although current revascularization therapies, such as percutaneous coronary interventions (PCI) and coronary artery bypass graft (CABG), improve the clinical outcomes of patients with coronary diseases, their application and therapeutic effects are limited in elderly patients. Thus, developing novel therapeutic strategies, like prompting collateral development or the process of arteriogenesis, is necessary for the treatment of the elderly with coronary diseases. Arteriogenesis (ie, the vascular remodeling from pre‐existent arterioles to collateral conductance networks) functions as an essential compensation for tissue hypoperfusion caused by artery occlusion or stenosis, and its mechanisms remain to be elucidated. In this review, we will summarize the roles of the major hydromechanical components in laminar conditions in arteriogenesis, and discuss the potential effects of disturbed flow components in non‐laminar conditions.

Computational fluid dynamics of a novel perfusion strategy during hybrid thoracic aortic repair

BACKGROUND AND AIM

To mitigate the risk of perioperative neurological complications during frozen elephant trunk procedures, we aimed to computationally evaluate the effects of direct cerebral perfusion strategy through a left carotid-subclavian bypass on hemodynamics in a patient-specific thoracic aorta model.

METHODS

Between July 2016 and March 2019, 11 consecutive patients underwent frozen elephant trunk operation using the left carotid-subclavian bypass with a side graft anastomosis and right-axillary cannulation for systemic and brain perfusion. A multiscale model realized coupling three-dimensional computational fluid dynamics was developed and validated with in vivo data. Model comparison with direct antegrade cannulation of all epiaortic vessels was performed. Wall shear stress, wall shear stress spatial gradient, and localized normalized helicity were selected as hemodynamic indicators. Four cerebral perfusion flows were tested (6 to 15 mL/kg/min).

RESULTS

Direct cerebral perfusion of the left subclavian bypass resulted in higher flow rates with augmented speeds in all epiaortic vessels in comparison with traditional perfusion model. At the level of the left vertebral artery (LVA), a speed of 22.5 vs 21 mL/min and mean velocity of 3.07 vs 2.93 cm/s were registered, respectively. With a cerebral perfusion flow of 15 mL/kg, lower LVA wall shear stress (1.596 vs 2.030 N/m² ), and wall shear stress gradient (1445 vs 5882 N/m³ ) were observed. A less disturbed flow considering the localized normalized helicity was documented. No patients experienced neurological/spinal cord damages.

CONCLUSIONS

Direct perfusion of a left carotid bypass proved to be cerebroprotective, resulting in a more physiological and stable anterior and posterior cerebral perfusion.

Fluid Shear Stress Induces Endothelial Cell Injury via Protein Kinase C Alpha-Mediated Repression of p120-Catenin and Vascular Endothelial Cadherin In Vitro

OBJECTIVE

The present study aimed to characterize the mechanism of fluid shear stress (FSS)-induced endothelial cell (EC) injury via protein kinase C alpha (PKCα)-mediated vascular endothelial cadherin (VE-cadherin) and p120-catenin (p120ctn) expression.

METHODS

We designed a T chamber system that produced stable FSS on ECs in vitro. Human umbilical vein endothelial cells (HUVECs) in which PKCα was knocked down and normal HUVECs were cultured on the coverslips. FSS was impinged on these 2 types of ECs for 0 hours and 6 hours. The morphology and density of HUVECs were evaluated, and expression levels of phosphorylated PKCα, p120-catenin (p120ctn), VE-cadherin, phosphorylated p120ctn at S879 (p-S879p120ctn), and nuclear factor kappa B (NF-κB) were analyzed by Western blot.

RESULTS

HUVECs exposed to FSS were characterized by a polygonal shape and decreased cell density. The phosphorylated PKCα level was increased under FSS at 6 hours (P < 0.05). In normal HUVECs during FSS, p120ctn and VE-cadherin were decreased, whereas p-S879p120ctn and NF-κB were increased, at 6 hours (P < 0.05). In HUVECs after PKCα knockdown, p120ctn and VE-cadherin were not significantly changed (P > 0.05), p-S879p120ctn was undetectable, but NF-κB was decreased (P < 0.05) at 6 hours.

CONCLUSIONS

The possible mechanism of FSS-induced EC injury may be as follows: 1) PKCα induces low expression of p120ctn, which leads to activation of NF-κB and degradation of VE-cadherin; 2) PKCα-mediated phosphorylation of p120ctn at S879 disrupts p120ctn binding to VE-cadherin.

Medical Image-Based Hemodynamic Analyses in a Study of the Pulmonary Artery in Children With Pulmonary Hypertension Related to Congenital Heart Disease

Objective: Pulmonary hypertension related to congenital heart disease (PH-CHD) is a devastating disease caused by hemodynamic disorders. Previous hemodynamic research in PH-CHD mainly focused on wall shear stress (WSS). However, energy loss (EL) is a vital parameter in evaluation of hemodynamic status. We investigated if EL of the pulmonary artery (PA) is a potential biomechanical marker for comprehensive assessment of PH-CHD. Materials and Methods: Ten PH-CHD patients and 10 age-matched controls were enrolled. Subject-specific 3-D PA models were reconstructed based on computed tomography. Transient flow, WSS, and EL in the PA were calculated using non-invasive computational fluid dynamics. The relationship between body surface area (BSA)-normalized EL ( E . ) and PA morphology and PA flow were analyzed. Results: Morphologic analysis indicated that the BSA-normalized main PA (MPA) diameter (D_MPAnorm), MPA/aorta diameter ratio (D_MPA/D_AO), and MPA/(left PA + right PA) [D_MPA/D_(LPA+RPA)] diameter ratio were significantly larger in PH-CHD patients. Hemodynamic results showed that the velocity of the PA branches was higher in PH-CHD patients, in whom PA flow rate usually increased. WSS in the MPA was lower and E . was higher in PH-CHD patients. E . was positively correlated with D_MPAnorm, D_MPA/D_AO, and D_MPA/D_(LPA+RPA) ratios and the flow rate in the PA. E . was a sensitive index for the diagnosis of PH-CHD. Conclusion: E . is a potential biomechanical marker for PH-CHD assessment. This hemodynamic parameter may lead to new directions for revealing the potential pathophysiologic mechanism of PH-CHD.

Investigation of the hemodynamic flow conditions and blood-induced stresses inside an abdominal aortic aneurysm by means of a SPH numerical model

The estimation of blood flow-induced loads occurring on the artery wall is affected by uncertainties hidden in the complex interaction of the pulsatile flow, the mechanical parameters of the artery, and the external support conditions. To circumvent these difficulties, a specific tool is developed by combining the aorta displacements measured by an electrocardiogram-gated-computed tomography angiography, with the blood velocity field computed by a smoothed particle hydrodynamics (SPH) numerical model. In the present work, the SPH model has been specifically adapted to the solution of the 3D Navier-Stokes equations inside a domain with boundaries of prescribed motion. Images of the abdominal aorta aneurysm (AAA) of a 44-year-old female patient were acquired during a stabilized cardiac cycle by electrocardiogram-gated-computed tomography angiography. The in vivo kinematic field inside the pulsating arterial wall was estimated by using recent technology, which makes it possible to follow the shape of the arterial wall during a cardiac cycle. We compare the flow conditions and the blood-induced loads, computed by the numerical model under the assumption of a moving arterial wall, with the corresponding results obtained assuming three rigid wall geometries of the vessel during the cardiac cycle. Significant differences were found for the wall shear stress distribution.

Association between basilar artery configuration and Vessel Wall features: a prospective high-resolution magnetic resonance imaging study

BACKGROUND

The relationship between intracranial vessel configuration and wall features remains poorly investigated. Therefore, we aimed to investigate the relationship between the distal and proximal anatomical configuration of basilar artery (BA) and BA vessel wall features on high-resolution magnetic resonance imaging (HRMRI).

METHODS

From September 2014 to January 2017, patients with suspected symptomatic intracranial arterial stenosis underwent HRMRI. Patients with severe BA stenosis were selected for this prospective study and divided into two groups corresponding to complete and incomplete BA configuration based on characteristics of the bilateral vertebral arteries and posterior cerebral arteries. Culprit blood vessel wall features on HRMRI included plaque enhancement, intraplaque hemorrhage, remodeling patterns, and plaque distribution. Culprit vessel wall features were compared between patients in the complete and incomplete BA configuration groups.

RESULTS

Among the 298 consecutively enrolled patients, 34 had severe BA stenosis. Twenty patients had complete anatomical BA configuration and another 14 of them displayed incomplete configuration. There were no significant differences in vessel wall features between the complete and incomplete configuration patient groups. However, the proximal configuration of BA was associated with intraplaque hemorrhage (p = 0.002) while the distal configuration of BA correlated with strong enhancement of BA plaque (p = 0.041).

CONCLUSIONS

No association was found between the complete and incomplete BA configuration groups and blood vessel wall features. The proximal configuration of BA was related with intraplaque hemorrhage and the distal configuration of BA was associated with strong plaque enhancement. Further studies are warranted to confirm these findings.

TRIAL REGISTRATION

URL: Unique identifier: NCT02705599 (March 10, 2016).

Carotid Bifurcation With Tandem Stenosis-A Patient-Specific Case Study Combined in vivo Imaging, in vitro Histology and in silico Simulation

A patient-specific carotid bifurcation with tandem stenosis found at both internal carotid artery (ICA) and common carotid artery (CCA) was studied. The in vivo pre-carotid endarterectomy (pre-CEA) multi-spectral magnetic resonance imaging (MRI) were performed and in vitro post-CEA carotid plaque tissue sample was collected. MR imaging data and tissue sample staining histology were used to recognize the plaque components. Further, the computational fluid dynamics (CFD) were performed on four MR-based reconstructed 3D carotid bifurcation models (the patient-specific geometry with tandem stenosis and three presumptive geometries by removing the stenosis part). The flow and shear stress behavior affected by the tandem stenosis was analyzed. From the results of MR segmentation and histology analysis, plaque lipid pool and calcification were found at both ICA and CCA. From the result of CFD simulation, the flow shear stress behavior suggested the tandem stenosis as a more “dangerous” situation than a single-stenosis artery. Besides, the CFD results deduced that the stenosis at the CCA location formed initially and led to the subsequent formation of stenosis at ICA. This study suggests that when planning CEA, CFD simulation on the presumptive models could help clinicians to estimate the blood flow behavior after surgery. Particular attention should be paid to the case of tandem stenosis, as the local hemodynamic environment is more complex and treatment of one stenosis may lead to a variation in the hemodynamic loading on the second plaque, which may result in either a higher risk of plaque rupture or restenosis.

Advances on fluid shear stress regulating blood-brain barrier

The integrity of structure and function of blood-brain barrier (BBB) plays a central role in maintaining the homeostasis of the central nervous system. Patients with severe cerebrovascular stenosis often undergo cerebrovascular bypass surgery. However, the sharply increased fluid shear stress (FSS) after cerebrovascular bypass disrupts the physiological function of brain microvascular endothelial cells (BMECs) at the lesion site, damaging BBB and inducing intracerebral hemorrhage eventually. At present, there are great interests in cerebral vascular flow regulating the structure and function of BBB under physiological and pathological conditions, and most of studies have highlighted the importance of BMECs in BBB. Understanding of how FSS regulating BBB can promote the development of new protective and restorative cerebral vascular interventional therapy.

Viscosity Estimation of a Suspension with Rigid Spheres in Circular Microchannels Using Particle Tracking Velocimetry

Suspension flows are ubiquitous in industry and nature. Therefore, it is important to understand the rheological properties of a suspension. The key to understanding the mechanism of suspension rheology is considering changes in its microstructure. It is difficult to evaluate the influence of change in the microstructure on the rheological properties affected by the macroscopic flow field for non-colloidal particles. In this study, we propose a new method to evaluate the changes in both the microstructure and rheological properties of a suspension using particle tracking velocimetry (PTV) and a power-law fluid model. Dilute suspension (0.38%) flows with fluorescent particles in a microchannel with a circular cross section were measured under low Reynolds number conditions (Re ≈ 10^-4). Furthermore, the distribution of suspended particles in the radial direction was obtained from the measured images. Based on the power-law index and dependence of relative viscosity on the shear rate, we observed that the non-Newtonian properties of the suspension showed shear-thinning. This method will be useful in revealing the relationship between microstructural changes in a suspension and its rheology.

Multivariate analysis of hemodynamic parameters on intracranial aneurysm initiation of the internal carotid artery

Although fluctuating hemodynamic wall stressors are known to impact intracranial aneurysms (IA) initiation, specificity of those stressors has not been evaluated. In this study, using human IA data, we investigated: (1) specificity of stressors in regions with and without IA eventual IA formation; and (2) how combinations of multiple stressors could improve IA formation prediction. 3D computational vasculatures were constructed based on angiographic images of 18 subjects having multiple closely-spaced IAs in the internal carotid artery. Two models were created: Model A with all IAs computationally removed, Model B which kept keep one IA. Computational fluid dynamics (CFD) simulated flow within models. Based on simulated flow fields, wall shear stress and its gradient (WSS, WSSG), oscillatory shear index (OSI), gradient oscillatory number (GON), aneurysm formation index (AFI), and mean number of swirling flow vortices (MV) were analysed. Multivariate logistic regression determined the accuracy of different combinations of those above-mentioned stressors. Overall, we found that combining hemodynamic stressors improves IA formation prediction over individual indices. Both Model A and Model B's parsimonious model was MV+WSS+GON: AUROC 0.88 and 0.83, respectively. Future studies are planned to understand biological meanings induced by fluctuating stressors.

Induction of aneurysmogenic high positive wall shear stress gradient by wide angle at cerebral bifurcations, independent of flow rate

OBJECTIVE

Endothelium adapts to wall shear stress (WSS) and is functionally sensitive to positive (aneurysmogenic) and negative (protective) spatial WSS gradients (WSSG) in regions of accelerating and decelerating flow, respectively. Positive WSSG causes endothelial migration, apoptosis, and aneurysmal extracellular remodeling. Given the association of wide branching angles with aneurysm presence, the authors evaluated the effect of bifurcation geometry on local apical hemodynamics.

METHODS

Computational fluid dynamics simulations were performed on parametric bifurcation models with increasing angles having: 1) symmetrical geometry (bifurcation angle 60°-180°), 2) asymmetrical geometry (daughter angles 30°/60° and 30°/90°), and 3) curved parent vessel (bifurcation angles 60°-120°), all at baseline and double flow rate. Time-dependent and time-averaged apical WSS and WSSG were analyzed. Results were validated on patient-derived models.

RESULTS

Narrow symmetrical bifurcations are characterized by protective negative apical WSSG, with a switch to aneurysmogenic WSSG occurring at angles ≥ 85°. Asymmetrical bifurcations develop positive WSSG on the more obtuse daughter branch. A curved parent vessel leads to positive apical WSSG on the side corresponding to the outer curve. All simulations revealed wider apical area coverage by higher WSS and positive WSSG magnitudes, with increased bifurcation angle and higher flow rate. Flow rate did not affect the angle threshold of 85°, past which positive WSSG occurs. In curved models, high flow displaced the impingement area away from the apex, in a dynamic fashion and in an angle-dependent manner.

CONCLUSIONS

Apical shear forces and spatial gradients are highly dependent on bifurcation and inflow vessel geometry. The development of aneurysmogenic positive WSSG as a function of angular geometry provides a mechanotransductive link for the association of wide bifurcations and aneurysm development. These results suggest therapeutic strategies aimed at altering underlying unfavorable geometry and deciphering the molecular endothelial response to shear gradients in a bid to disrupt the associated aneurysmal degeneration.

The Geometric Effects on the Stress of Arterial Atherosclerotic Plaques: a Computational Study

BACKGROUND

The rupture of atherosclerotic plaques could cause serious clinical events. The wall shear stress (WSS) and axial plaque stress (APS) could reflect the risk of plaque rupture. This study aimed to quantitatively investigate the geometric effects on WSS and APS using computational fluid dynamics (CFD).

METHODS

63 plaque models were developed from three severities (75%, 82%, and 89% in area), three eccentricities (the deviation of plaque throat from the arterial centerline: 0, 0.375 and 0.75mm), and 7 different length combinations of the proximal and distal stenotic segments (2mm-5mm, 3mm-5mm, 4mm-5mm, 5mm-5mm, 5mm-4mm, 5mm-3mm, 5mm-2mm). For each model, CFD simulation was performed to calculate the maximum and area-averaged WSS and APS on the proximal and distal stenotic segments. The multivariate analysis of variance and linear regression analysis were performed to quantitatively investigate the geometry-stress relationship.The results showed that, the severity and eccentricity of a plaque were linearly related to its WSS and APS. APS value on a segment (proximal or distal) of the plaque depended on the segmental length It was also shown that the difference of APS between proximal and distal segments depended exclusively on the difference of length between segments (all p<; 0.05).

CONCLUSION

The geometry of a plaque influences its WSS and APS. APS and its proximal/distal difference depend on the segmental lengths.

Shear stress and aneurysms: a review

Wall shear stress, the frictional force of blood flow tangential to an artery lumen, has been demonstrated in multiple studies to influence aneurysm formation and risk of rupture. In this article, the authors review the ways in which shear stress may influence aneurysm growth and rupture through changes in the vessel wall endothelial cells, smooth-muscle cells, and surrounding adventitia, and they discuss shear stress–induced pathways through which these changes occur.

Prediction of restenosis based on hemodynamical markers in revascularized femoro-popliteal arteries during leg flexion

Endovascular therapy in patients suffering from peripheral arterial disease shows high rates of restenosis. The poor clinical outcomes are commonly explained by the demanding mechanical environment due to leg movements, but the mechanisms responsible for restenosis remain unknown. In this study, we hypothesized that restenosis following revascularization is associated with hemodynamical markers derived from blood flow during leg flexion. Therefore, we performed personalized computational fluid dynamics (CFD) analyses of 20 patients, who underwent routine endovascular femoro-popliteal interventions. The CFD analyses were conducted using 3D models of the arterial geometry in straight and flexed positions, which were reconstructed from 2D angiographic images. Based on restenosis rates reported at 6-month follow-up, logistic regression analyses were performed to predict restenosis from hemodynamical parameters. Results showed that severe arterial deformations, such as kinking, induced by leg flexion in stented arteries led to adverse hemodynamic conditions that may trigger restenosis. A logistic regression analysis based solely on hemodynamical markers had an accuracy of 75%, which showed that flow parameters are sufficient to predict restenosis (p = 0.031). However, better predictions were achieved by adding the treatment method in the model. This suggests that a more accurate image acquisition technique is required to capture the localized modifications of blood flow following intervention, especially around the stented artery. This approach, based on the immediate postoperative configuration of the artery, has the potential to identify patients at increased risk of restenosis. Based on this information, clinicians could take preventive measures and more closely follow these patients to avoid complications.

Vascular tortuosity of the internal carotid artery is related to the RNF213 c.14429G > A variant in moyamoya disease

Recent studies have implicated RNF213 mutations in the pathogenesis of moyamoya disease (MMD). However, the underlying mechanism of disease development is not fully elucidated. Nonetheless, a possible relationship between vascular morphology and hemodynamics related with MMD has been proposed. Here, we aimed to investigate the relationship between a variant of RNF213 and the morphology of the internal carotid artery (ICA). We enrolled bilateral MMD patients who had undergone genetic testing for RNF213. Patients were divided into mutant and wild-type groups. Six anatomy-specific three-dimensional coordinates were collected using magnetic-resonance angiography. From these, five vectors between two adjacent points and four angles between two adjacent vectors were calculated. The tortuosity was defined as the ratio between the actual and the linear length of the ICAs. Among 58 patients, 44 and 14 belonged to the mutant and wild-type groups, respectively. The tortuosity of ICAs was significantly lower in the mutant group (p = 0.010). The change in blood flow direction was more prominent in the wild-type group (p = 0.002). The tortuosity was significantly lower in MMD patients than normal controls (p < 0.001). Our results indicate that RNF213 could play a role in the lower tortuosity observed in patients with RNF213 mutation.

Computational fluid dynamics simulations as a complementary study for transcatheter endovascular stent implantation for re-coarctation of the aorta associated with minimal pressure drop: an aneurysmal ductal ampulla with aortic isthmus narrowing

BACKGROUND

Transcatheter stent implantation has been employed to treat re-coarctation of the aorta in adolescents and young adults. The aim of this work is to use computational fluid dynamics to characterise haemodynamics associated with re-coarctation involving an aneurysmal ductal ampulla and aortic isthmus narrowing, which created minimal pressure drop, and to incorporate computational fluid dynamics's findings into decision-making concerning catheter-directed treatment.

METHODS

Computational fluid dynamics permits numerically solving the Navier-Stokes equations governing pulsatile flow in the aorta, based on patient-specific data. We determined flow-velocity fields, wall shear stresses, oscillatory shear indices, and particle stream traces, which cannot be ascertained from catheterisation data or magnetic resonance imaging.

RESULTS

Computational fluid dynamics showed that, as flow entered the isthmus, it separated from the aortic wall, and created vortices leading to re-circulating low-velocity flow that induced low and multidirectional wall shear stress, which could sustain platelet-mediated thrombus formation in the ampulla. In contrast, as flow exited the isthmus, it created a jet leading to high-velocity flow that induced high and unidirectional wall shear stress, which could eventually undermine the wall of the descending aorta.

SUMMARY

We used computational fluid dynamics to study re-coarctation involving an aneurysmal ductal ampulla and aortic isthmus narrowing. Despite minimal pressure drop, computational fluid dynamics identified flow patterns that would place the patient at risk for: thromboembolic events, rupture of the ampulla, and impaired descending aortic wall integrity. Thus, catheter-directed stenting was undertaken and proved successful. Computational fluid dynamics yielded important information, not only about the case presented, but about the complementary role it can serve in the management of patients with complex aortic arch obstruction.