Blood Flow Dynamics Research Articles

Analysis of microcirculatory blood flow parameters during a course of transcutaneous electrical stimulation in men with newly diagnosed arterial hypertension

Objective. To study the dynamics of microcirculatory blood flow in the skin during a course of use of the electrical stimulator AVR-051 in men of low and moderate cardiovascular risk with newly diagnosed arterial hypertension. Materials and methods. The single-center placebo-controlled study included 44 men of working age (30–60 years) with low and moderate cardiovascular risk with newly diagnosed hypertension, who were randomly divided into 2 groups. The control group (CG) included 30 men who underwent electrical stimulation with a commercial device. The placebo group (PG) included 14 men who used the AVR-051 device, with the electrostimulation function disabled. The study design included 3 visits. After visit 1 and randomization, the subjects underwent electrical stimulation/sham at home 2 times a day for 14 days. Visit 2 was carried out immediately after the end of the physiotherapy course, visit 3 was 14 days after visit 2. At each visit, a one-stage comprehensive study of microcirculation (video capillaroscopy, laser Doppler flowmetry and photoplethysmography) and 24-hour blood pressure monitoring on the left upper limb were performed. Results. In the CG, while blood pressure decreased at visits 2 and 3 by 5.5/3.5 and 7.5/3.5 mm Hg relative to the initial values, statistically significant changes at the level of the microvascular bed were recorded only at visit 3: an increase in the functional density of the capillary network by 10 cap/mm2, an increase in the amplitude of pulse oscillations of blood flow from 0.68 to 1.06 PU and the perfusion contribution of pulse oscillations from 3.89 to 8.22 %, a decrease in the augmentation index from 6.25 to 3.2 %, a decrease in the stiffness index from 7.45 to 7 cm/s and the reflection index from 37.4 to 30.2 %, respectively. In the GP, no reliable dynamics was recorded for any of the analyzed parameters. Conclusion. Positive dynamics at the level of the microvascular bed of the skin is a consequence of a decrease in blood pressure level against the background of systemic normalization of sympathetic tone. After the course of electrical stimulation, a hypotensive effect is observed in 86.7 % of men at early stages of the hypertension development, and in 20 % of them, a complete normalization of blood pressure level is observed.

Upper cervical sympathectomy in neurovascular pathology.

The effectiveness of upper cervical sympathectomy in the treatment of patients with neurovascular pathology has been discussed in the researcher’s article for many years. However, the indications for this surgery need still to be clarified. The dynamics of cerebral blood flow during sympathetic blockade could not become the significant criterion for determining indications for surgical treatment. A cerebral perfusion pressure change in neurovascular pathology can activate the neurogenic mechanism of cerebral blood flow regulation. The need to search for new methods for the intensity of the autonomic nervous system impact on the cerebral vessels tone (the neurogenic mechanism of cerebral blood flow regulation) to clarify the indications for upper cervical sympathectomy in patients with neurovascular pathology is justified. The review put forward a hypothesis about the relationship between intracranial B-waves amplitude and the state of the neurogenic mechanism of cerebral blood flow regulation.

The Assessment of the Vascular Risk for Facial Procedures using Thermal Scanning Imaging and Doppler Ultrasonography

Introduction: Surgical and non-surgical facial procedures have gained immense popularity thanks to their aesthetic benefits. Understanding the vascularization of the face and assessing potential risks is crucial to ensure patient safety and optimal outcomes. This study aims to evaluate the utility of thermal scanning and Doppler ultrasonography in evaluating the vascular risk for facial procedures. Material and Methods: A cohort of 60 patients were included in this prospective study. Preoperative thermal scanning and Doppler ultrasonography were performed in order to visualize the facial vasculature and identify potential areas of risk. Results: For 30 patients, we performed preprocedural Doppler ultrasound imaging and thermal scanning at the injection site. Only 6.66% of them suffered vascular complications, whilst 23.33% among those who didn’t undergo ultrasound and thermoscanning suffered vascular injuries. The combined use of these tools proved to be valuable in assessing the vascular risk for facial procedures. The findings emphasize the importance of preoperative assessment to identify patients at risk for vascular complications. Conclusions: Thermal scanning and Doppler ultrasonography offer a comprehensive approach to assessing the vascular risk for facial procedures. By ensuring the identification of abnormal vascular patterns and altered blood flow dynamics, these techniques enhance patient safety and procedure planning.

Intraprocedural C-arm dual-phase cone-beam enhancement patterns correlate with tumor absorbed dose after radioembolization.

Recent studies have shown a clear relationship between absorbed dose and tumor response to treatment after hepatic radioembolization. These findings help to create more personalized treatment planning and dosimetry. However, crucial to this goal is the ability to predict the dose distribution prior to treatment. The microsphere distribution is ultimately determined by (i) the hepatic vasculature and the resulting blood flow dynamics and (ii) the catheter position. To show that pretreatment, intra-procedural imaging of blood flow patterns, as quantified by catheter-directed intra-arterial contrast enhancement, correlate with posttreatment microsphere accumulation and, consequently, absorbed dose. Patients who participated in a clinical trial (NCT01177007) and for whom both a pretreatment dual-phase contrast-enhanced cone-beam CT (CBCT) and a posttreatment 90Y PET/CT scan were available were included in this retrospective study. Tumors and perfused volumes were manually delineated on the CBCT by an experienced radiologist. The mean, sum, and standard deviation of the voxels in each volume were recorded. The delineations were transferred to the PET-based absorbed dose maps by coregistration of the corresponding CTs. Linear multiple regression was used to correlate pretreatment CBCT enhancement to posttreatment 90Y PET/CT-based absorbed dose in each region. Leave-one-out cross-validation and Bland-Altman analyses were performed on the predicted versus measured absorbed doses. Nine patients, with a total of 23 tumors were included. All presented with hepatocellular carcinoma (HCC). Visually, all patients had a clear correspondence between CBCT enhancement and absorbed dose. The correlation between CBCT enhancement and posttherapy absorbed tumor dose based was strong (R2=0.91), and moderate for the non-tumor liver tissue (R2=0.61). Limits of agreement were approximately ±55 Gray for tumor tissue. There is a linear relationship between pretreatment blood dynamics in HCC tumors and posttreatment absorbed dose, which, if shown to be generalizable, allows for pretreatment tumor absorbed dose prediction.

Goreisan regulates cerebral blood flow according to barometric pressure fluctuations in female C57BL/6J mice

Goreisan is a Kampo medicine used to treat headaches associated with climate change. Here, by using an implantable complementary metal-oxide-semiconductor (CMOS) device, we evaluated the effects of Goreisan and loxoprofen on cerebral blood flow (CBF) dynamics associated with barometric pressure fluctuations in freely moving mice. In the vehicle group, decreasing barometric pressure increased CBF that was prevented by Goreisan and loxoprofen. Notably, Goreisan, but not loxoprofen, reduced CBF after returning to atmospheric pressure. These results indicate that, unlike the mechanism of action of antipyretic analgesics, Goreisan normalizes CBF abnormalities associated with barometric pressure fluctuations by actively reducing CBF increase.

Impact of Multi-Grade Localized Calcifications on Aortic Valve Dynamics under Helical Inflow: A Comparative Hemodynamic Study

This study investigates the hemodynamic impacts of localized aortic valve calcification, utilizing immersed boundary-finite element (IBFE) method simulations with realistic inflow patterns of uniform and helical blood flow from the left ventricular outflow tract (LVOT). We modeled the aortic valve leaflets with varying grades of calcification, assessing their influence on valve performance, including transvalvular hemodynamics, wall shear stress (WSS) indices, and vortical structures. The findings highlighted that calcification significantly restricts leaflet motion, diminishes the orifice area, disrupts flow efficiency, and consequently increases the left ventricular workload. Advanced calcification resulted in elevated WSS, especially at the leaflet tips, which indicates a heightened risk of endothelial damage and further calcification. Asymmetrical calcifications redirect flow towards the ascending aorta wall, potentially inducing structural damage and increased stress on the remaining healthy leaflets. Calcification was also found to alter the naturally occurring helical blood flow patterns, affecting the system’s fluid transport efficiency and possibly contributing to cardiovascular disease progression. The study revealed a significant alteration in vortex formation, with calcification causing distorted and complex vortex structures, which may influence the dynamics of blood flow and valve function. These insights into the hemodynamic changes induced by calcification contribute to a better understanding of the progression of aortic valve diseases and could inform more effective diagnostic and treatment strategies.

Heterogeneity of endothelial VE-PTP downstream polarization, Tie2 activation, junctional claudin-5, and permeability in the aorta and vena cava

Endothelial cells of mammalian blood vessels have multiple levels of heterogeneity along the vascular tree and among different organs. Further heterogeneity results from blood flow turbulence and variations in shear stress. In the aorta, vascular endothelial protein tyrosine phosphatase (VE-PTP), which dephosphorylates tyrosine kinase receptor Tie2 in the plasma membrane, undergoes downstream polarization and endocytosis in endothelial cells exposed to laminar flow and high shear stress. VE-PTP sequestration promotes Tie2 phosphorylation at tyrosine992 and endothelial barrier tightening. The present study characterized the heterogeneity of VE-PTP polarization, Tie2-pY992 and total Tie2, and claudin-5 in anatomically defined regions of endothelial cells in the mouse descending thoracic aorta, where laminar flow is variable and IgG extravasation is patchy. We discovered that VE-PTP and Tie2-pY992 had mosaic patterns, unlike the uniform distribution of total Tie2. Claudin-5 at tight junctions also had a mosaic pattern, whereas VE-cadherin at adherens junctions bordered all endothelial cells. Importantly, the amounts of Tie2-pY992 and claudin-5 in aortic endothelial cells correlated with downstream polarization of VE-PTP. VE-PTP and Tie2-pY992 also had mosaic patterns in the vena cava, but claudin-5 was nearly absent and extravasated IgG was ubiquitous. Correlation of Tie2-pY992 and claudin-5 with VE-PTP polarization supports their collective interaction in the regulation of endothelial barrier function in the aorta, yet differences between the aorta and vena cava indicate additional flow-related determinants of permeability. Together, the results highlight new levels of endothelial cell functional mosaicism in the aorta and vena cava, where blood flow dynamics are well known to be heterogeneous.

Learning reduced-order models for cardiovascular simulations with graph neural networks

Reduced-order models based on physics are a popular choice in cardiovascular modeling due to their efficiency, but they may experience loss in accuracy when working with anatomies that contain numerous junctions or pathological conditions. We develop one-dimensional reduced-order models that simulate blood flow dynamics using a graph neural network trained on three-dimensional hemodynamic simulation data. Given the initial condition of the system, the network iteratively predicts the pressure and flow rate at the vessel centerline nodes. Our numerical results demonstrate the accuracy and generalizability of our method in physiological geometries comprising a variety of anatomies and boundary conditions. Our findings demonstrate that our approach can achieve errors below 3% for pressure and flow rate, provided there is adequate training data. As a result, our method exhibits superior performance compared to physics-based one-dimensional models while maintaining high efficiency at inference time.

Compressed SVD-based L + S model to reconstruct undersampled dynamic MRI data using parallel architecture.

Magnetic Resonance Imaging (MRI) is a highly demanded medical imaging system due to high resolution, large volumetric coverage, and ability to capture the dynamic and functional information of body organs e.g. cardiac MRI is employed to assess cardiac structure and evaluate blood flow dynamics through the cardiac valves. Long scan time is the main drawback of MRI, which makes it difficult for the patients to remain still during the scanning process. By collecting fewer measurements, MRI scan time can be shortened, but this undersampling causes aliasing artifacts in the reconstructed images. Advanced image reconstruction algorithms have been used in literature to overcome these undersampling artifacts. These algorithms are computationally expensive and require a long time for reconstruction which makes them infeasible for real-time clinical applications e.g. cardiac MRI. However, exploiting the inherent parallelism in these algorithms can help to reduce their computation time. Low-rank plus sparse (L+S) matrix decomposition model is a technique used in literature to reconstruct the highly undersampled dynamic MRI (dMRI) data at the expense of long reconstruction time. In this paper, Compressed Singular Value Decomposition (cSVD) model is used in L+S decomposition model (instead of conventional SVD) to reduce the reconstruction time. The results provide improved quality of the reconstructed images. Furthermore, it has been observed that cSVD and other parts of the L+S model possess highly parallel operations; therefore, a customized GPU based parallel architecture of the modified L+S model has been presented to further reduce the reconstruction time. Four cardiac MRI datasets (three different cardiac perfusion acquired from different patients and one cardiac cine data), each with different acceleration factors of 2, 6 and 8 are used for experiments in this paper. Experimental results demonstrate that using the proposed parallel architecture for the reconstruction of cardiac perfusion data provides a speed-up factor up to 19.15× (with memory latency) and 70.55× (without memory latency) in comparison to the conventional CPU reconstruction with no compromise on image quality. The proposed method is well-suited for real-time clinical applications, offering a substantial reduction in reconstruction time.

Dynamic blood flow imaging with 99mTc-hydroxymethylene diphosphonate as a therapeutic response marker in patients with Raynaud's phenomenon.

We evaluated the predictive value of dynamic blood flow scintigraphy with 99mTc-HDP (hydroxymethylene diphosphonate) for therapeutic response in patients with Raynaud's phenomenon (RP). Eighty patients who underwent dynamic blood flow scintigraphy using the one-hand chilling method were enrolled. We analyzed the quantitative variables as the ratio of chilled fingers to ambient fingers (CAfinger), that of the chilled hand to ambient hand (CAhand), and that of chilled fingers to ambient palm (FPR) (CAFPR) at 15 and 30s after 99mTc-HDP bolus injection. Total cumulative radioactivity counts for 180s were obtained. We evaluated the clinical utility of these quantitative parameters with other clinical variables, including RP severity, therapeutic compliance, types of RP, and scintigraphic interpretation of findings in patients with RP. Fifty-two patients showed poor therapeutic response. There were significant differences between good- and poor-therapeutic responder groups in RP intensity (p = 0.003), CAfinger15s (p = 0.008), CAfinger30s (p = 0.002), CAfinger180s (p = 0.011), CAhand15s (p = 0.008), CAhand30s (p = 0.007), CAhand180s (p = 0.017), CAFPR30s (p = 0.004), and CAFPR180s (p = 0.002). After multivariate logistic regression analysis, only CAfinger30s (p = 0.002) had an independent predictive value of the therapeutic response. 99mTc-HDP dynamic blood flow scintigraphy could be helpful in predicting the therapeutic response in patients with RP.

Abstract 17083: Aortic Luminal Contrast Attenuation Varies With Dissection Morphology and is Associated With Need For Intervention

Introduction: Prognostication after acute Type B aortic dissection (aTBAD) may be limited when relying upon static computed tomographic angiography (CTA) images to evaluate a dynamic process. We performed an exploratory study to characterize variations in luminal contrast attenuation on CTA, as a surrogate for blood flow in dissection, and to determine whether the resulting parameters held prognostic value. Methods: Retrospective, single-institution data for patients with aTBAD were gathered from 1999-2020. Patients with prior dissection repairs were excluded. Dissection morphology was classified by the SVS/STS scheme and location/number of fenestrations. Hounsfield unit ratios (HUR) comparing lumina, phases, and aortic zone were calculated. Aortic growth, false lumen thrombosis, and need for intervention were evaluated with univariable logistic regression. Results: After exclusions, 85 patients were identified (mean age 61.9 years, 69.4% male). SVS/STS B 3,10 (20%) and B 3,5 (12.9%) predominated (Figure). Most fenestrations were in Zone 4/5 (56.5%) and associated with more equilibrated HUR (0.93) compared to dissections without fenestration (0.70, p = 0.04). Fenestration zone was not associated with HUR ( p = 0.59). Intervention occurred in 65.9%, most often for aneurysmal degeneration (43.8%), followed by visceral/limb ischemia (32.6%). Growth occurred in 28.2%. Increased arterial false-to-true HUR was strongly associated with eventual need for intervention (OR 25.3 [95% CI 4.15-188.4], p = 0.001) while increased delayed-to-arterial false lumen HUR was associated with decreased intervention (OR 0.49 [95% CI 0.25-0.89], p = 0.02). Conclusion: In patients with aTBAD, calculated permutations of HUR across lumina and between CTA phases may give insight into blood flow dynamics, which in turn likely impact need for intervention. Future prospective studies of time-resolved CTA are likely to hold significant prognostic value and alter management.

Abstract 14190: Simultaneous Analysis of Myocardial Flow Reserve and Intra-Ventricular 4D Flow Using Hybrid 13 N-ammonia Positron Emission Tomography/Magnetic Resonance Imaging in Patients With Coronary Artery Disease

Introduction: Intra-left ventricular (LV) blood flow dynamics is closely related to wall kinetics and myocardial perfusion. 4D flow magnetic resonance imaging (MR) has been developed to simulate and quantify intra-LV blood flow. We aimed to evaluate the usefulness of simultaneous analysis of myocardial flow reserve (MFR) and intra-LV 4D flow measured by hybrid 13 N-ammonia positron emission tomography (PET)/MR in patients with coronary artery disease (CAD). Methods: Forty patients (mean 65±18 years, male 32) with CAD who underwent pharmacological stress PET/MR were enrolled. MFR was calculated from a series of dynamic rest-stress PET scans. Simultaneously, 4D flow MR acquisition was performed during the stress PET scan. The intra-LV 4D flow was visually assessed, where the smooth flow was defined as normal pattern, and random, or reverse flow was defined as abnormal (Figure A). The velocity of LV inflow and outflow were measured. Results: A normal flow pattern was found in 22 patients, while abnormal pattern was found in 18. MFR showed a significant correlation with the velocity of LV inflow and outflow (inflow: R = 0.552, P < 0.001; outflow: R = 0.563, P < 0.001). MFR was significantly lower in the abnormal flow compared to the normal flow (1.484 ± 0.559 vs. 1.931 ± 0.775, P = 0.041, Figure B). Additionally, when analyzing MFR in coronary artery territories, MFR in the left anterior descending artery was significantly lower in the abnormal flow compared to the normal flow (1.405 ± 0.526 vs. 1.881 ± 0.791, P = 0.029, Figure C). Conclusion: Simultaneous analysis of MFR and intra-LV 4D flow has a potential to serve as a novel indicator for assessing the severity of ischemia in patients with CAD.

Abstract 13614: Nationwide Trends in Transcranial Doppler Utilization During Acute Ischemic Stroke Hospitalizations

Background: Trans-cranial Doppler (TCD), diagnostic ultrasound of the head and neck is a non-invasive, safe, and portable tool to assess dynamic cerebral blood flow. TCD allows us to explore the patient's neurocritical pathological features without invasive testing. Although TCD is portable and inexpensive compared to CT/MR angiograms, its utilization during AIS hospitalization is nonfrequent and unknown. Aim: The aim of the study was to evaluate the patterns of TCD use during AIS hospitalizations. Design/Methods: Data from the Nationwide Inpatient Sample (NIS-2003-2014) for adults (≥18 yr) were analyzed. Primary discharge diagnoses of AIS and TCD were identified using ICD-9-CM codes 433-436, 437.1, and 88.71, respectively. Cochran-Armitage trend test and multivariable survey logistic regression were utilized to evaluate TCD use and predictors. Results: Of 4,224,924 patients identified with AIS 93,673 (2.22%) had TCD examination. There was a significant decline in utilization of TCD (3.84% in 2003 to 1.34% in 2014, p<0.0001). The patients with TCD utilization had a higher mean length of stay (6 vs 5 days; p<0.0001) and cost of hospitalization ($39,270 vs $38,100; p=0.0007) than non-TCD utilization. In multivariate regression analysis, age group 50-64 (aOR:1.55; 95%CI:1.28-1.88), 65-79 (1.66; 1.32-2.08), ≥80 (1.68; 1.29-2.18), African American (1.51; 1.45-1.58), Hispanic (1.63; 1.55-1.72), Asian/Pacific Islander (1.36; 1.26-1.47), zip income 76-100th percentile (1.24; 1.19-1.30), large bed size hospitals (1.44; 1.36-1.52), hypertension (1.05; 1.01-1.09), hypercholesterolemia (1.23; 1.18-1.29; p<0.0001), alcohol abuse (1.09; 1.00-1.18), anticoagulant use (1.47; 1.39-1.56), ischemic heart disease (1.05; 1.01-1.09), and ventricular septal defect (2.69; 1.31-5.52) have higher odds of TCD utilization. We have noticed lower odds of TCD utilization in elective admissions (0.65; 0.59-0.72). (c-statistic: 0.71) Conclusions: Over the last decade, there has been a slight but steady decrease in the use of TCD during AIS hospitalizations in the US. Future studies should examine the cost-utility of TCD, especially with the advent of endovascular stroke treatment systems.

Adipose inflammation: South Asian ethnicity and central obesity are independently associated with higher immune cell recruitment to adipose-specific media: A pilot study in men.

A South Asian (SA) cardiovascular phenomenon exists whereby SAs have excess burden of cardiovascular disease (CVD) despite having low prevalence of recognized CVD risk factors. The aim of the current study was to determine whether perturbations in monocyte biology contribute to this phenomenon via higher circulating cell numbers, a more pro-inflammatory phenotype, and higher transmigration and adhesion. Adhesion is linked to vascular inflammation whereas transmigration is linked to tissue inflammation. SA men with (N = 10; SAs with central obesity [CO-SA]) and without (N = 10; lean SA [LE-SA]) central obesity, plus White European counterparts (N = 10; white Europeans with central obesity [CO-WE], N = 10; lean white Europeans [LE-WE]) participated. An exvivo assay mimicking blood flow dynamics coupled to flow cytometry determined the adhesion and transmigration of monocyte subsets toward chemokine-rich media cultured from pre-adipocytes (absolute responses). Migration and adhesion were also standardized for differences in numbers of circulating monocytes between participants (relative responses). Metabolic and inflammatory markers were assessed. SAs had higher absolute (but not relative) adhesion and migration of monocytes than WEs. Central obesity was associated with higher absolute and relative adhesion and migration of monocytes. SAs had higher concentrations of all monocyte subsets compared with WEs coinciding with adverse cardiovascular-inflammatory profiles. LE-SAs had similar monocyte concentrations, transmigration, and adhesion compared with CO-WEs, corresponding with similar cardiovascular-inflammatory profiles. The study provides novel evidence for higher monocyte counts associated with higher transmigration and adhesion in SA compared with WE men. Importantly, similar monocyte biology and cardiovascular-inflammatory profiles were seen in LE-SAs compared with CO-WEs, which may contribute to the higher risk of CVD at lower body mass index experienced by SAs.

Abstract 101: Ophthalmic Artery Aneurysm Embolization Resulting in Resolution of Headaches and Visual Symptoms

Introduction Cerebral aneurysms are a rare cause of headaches and visual symptoms. Most common locations include anterior communicating artery, internal carotid arteries (ICAs), middle cerebral arteries, and tip of the basilar artery. While most unruptured aneurysms are asymptomatic, when symptoms do occur, they are most often headaches, cranial nerve palsies, or bilateral temporal hemianopsia due to compression of surrounding nerves or the optic chiasm. Rarely, thrombus formation within an aneurysm can lead to symptoms via distal embolization and infarction. The literature is limited regarding repeated aneurysmal microembolism formation or transient alterations in blood flow dynamics leading to episodic symptoms. Methods We report the case of a 55 year‐old woman with Ehlers‐Danlos syndrome and syringomyelia who presented to the hospital with one week of intermittent left eye visual disturbances, characterized by either complete transient monocular vision loss or blurriness lasting for 30 seconds at a time and occurring multiple times per day. These symptoms were also associated with pressure‐like headaches that originated around the left eye and radiated to the left side of her head. Results Neurological and ophthalmological examinations were notable for normal cranial nerve function, including intact visual acuity, visual fields, color vision and extraocular movements in each eye. On a dilated fundoscopic exam, there were no retinal or optic disc abnormalities. The rest of the neurological exam was normal. Head and neck CTA and subsequent digital subtraction angiography (DSA) showed multiple bilateral ICA aneurysms, as well as a 4 millimeter left ophthalmic artery aneurysm. Brain and orbits MRI with contrast showed no acute abnormalities, including no evidence of infarction or intracranial hemorrhage. She was started on clopidogrel due to concern for recurrent retinal transient ischemic attacks as well as escalating doses of nortriptyline for empiric treatment of possible ocular migraines. In follow‐up three months later, she continued to have the same visual and headaches symptoms. She underwent a successful elective flow diversion embolization of the ophthalmic artery aneurysm with subsequent resolution of her symptoms Conclusion Here we describe a case of a patient who presented with episodic monocular vision changes and headaches ipsilateral to an ophthalmic artery aneurysm, who experienced complete resolution of these symptoms following flow diversion embolization of the aneurysm. Although the precise pathophysiological relationship between the aneurysm and her visual symptoms is unclear, potential mechanisms include aneurysmal microthrombus formation with retinal embolization and dissolution, hemodynamic retinal blood flow changes related to the aneurysm, or recurrent ocular migraines triggered by the ophthalmic artery aneurysm.

Non-Newtonian pulsatile blood flow through the stenosed arteries: comparison between the viscoelastic and elastic arterial wall in response to the alterations

:In this study, we investigate the impact of aortic stenosis on the hemodynamics of pulsatile blood flow within a 3D aortic model. Employing a non-Newtonian Casson model with a hematocrit of 45%, our study introduces a preliminary hypothesis to simulate blood flow dynamics, incorporating both linear elastic and viscoelastic models to define the mechanical characteristics of the artery. Through simulations conducted with Ansys-Cfx (version 15), we utilize a 2-way fluid-structure interaction (FSI) approach, employing a Lagrangian-Eulerian formulation with second-order accuracy. We explore the influence of stenosis severity on variables including velocity profiles, pressure distribution, shear stress, wall displacement, and changes in the OSI parameter. Our investigation encompasses arteries with both elastic and viscoelastic walls. The key findings that arise from our results highlight the viscoelastic model’s demonstration of reduced radial wall displacement when compared to the linear elastic model. Additionally, we observe that elevated arterial stenosis percentages lead to the elongation of vortex length, heightened wall shear stress, and increased slope of velocity profiles downstream of the stenosed region. Furthermore, bulky obstruction of viscoelastic arteries as opposed to elastic, resulted in a maximum 5 percent increase in velocity profile and a 29.6% decrease in radial displacement. The zenith of shear stress occurs concomitantly with the velocity’s peak within the stenosed area. Viscoelastic arterial wall shear stress at the stenosis site escalates due to the rapid expansion of the stenosis. The viscoelastic wall, responding with a blend of viscous and elastic characteristics to applied stress, undergoes slight deformation in shape. Following stress reduction, the wall gradually reverts to its original form, thus alleviating some of the applied stress. In contrast, the elastic wall retains its altered shape due to stress preservation within the material. Additionally, we ascertain an augmentation in radial displacement corresponding with increased artery stenosis.

Pressure–Poisson equation in numerical simulation of cerebral arterial circulation and its effect on the electrical conductivity of the brain

Background and ObjectiveThis study considers dynamic modeling of the cerebral arterial circulation and reconstructing an atlas for the electrical conductivity of the brain. Electrical conductivity is a governing parameter in several electrophysiological modalities applied in neuroscience, such as electroencephalography (EEG), transcranial electrical stimulation (tES), and electrical impedance tomography (EIT). While high-resolution 7-Tesla (T) Magnetic Resonance Imaging (MRI) data allow for reconstructing the cerebral arteries with a cross-sectional diameter larger than the voxel size, electrical conductivity cannot be directly inferred from MRI data. Brain models of electrophysiology typically associate each brain tissue compartment with a constant electrical conductivity, omitting any dynamic effects of cerebral blood circulation. Incorporating those effects poses the challenge of solving a system of incompressible Navier–Stokes equations (NSEs) in a realistic multi-compartment head model. However, using a simplified circulation model is well-motivated since, on the one hand, the complete system does not always have a numerically stable solution and, on the other hand, the full set of arteries cannot be perfectly reconstructed from the MRI data, meaning that any solution will be approximative. MethodsWe postulate that circulation in the distinguishable arteries can be estimated via the pressure–Poisson equation (PPE), which is coupled with Fick's law of diffusion for microcirculation. To establish a fluid exchange model between arteries and microarteries, a boundary condition derived from the Hagen–Poisseuille model is applied. The relationship between the estimated volumetric blood concentration and the electrical conductivity of the brain tissue is approximated through Archie's law for fluid flow in porous media. ResultsThrough the formulation of the PPE and a set of boundary conditions (BCs) based on the Hagen–Poisseuille model, we obtained an equivalent formulation of the incompressible Stokes equation (SE). Thus, allowing effective blood pressure estimation in cerebral arteries segmented from open 7T MRI data. ConclusionsAs a result of this research, we developed and built a useful modeling framework that accounts for the effects of dynamic blood flow on a novel MRI-based electrical conductivity atlas. The electrical conductivity perturbation obtained in numerical experiments has an appropriate overall match with previous studies on this subject. Further research to validate these results will be necessary.

Advances in laser speckle imaging: From qualitative to quantitative hemodynamic assessment.

Laser speckle imaging (LSI) techniques have emerged as a promising method for visualizing functional blood vessels and tissue perfusion by analyzing the speckle patterns generated by coherent light interacting with living biological tissue. These patterns carry important biophysical tissue information including blood flow dynamics. The noninvasive, label-free, and wide-field attributes along with relatively simple instrumental schematics make it an appealing imaging modality in preclinical and clinical applications. The review outlines the fundamentals of speckle physics and the three categories of LSI techniques based on their degree of quantification: qualitative, semi-quantitative and quantitative. Qualitative LSI produces microvascular maps by capturing speckle contrast variations between blood vessels containing moving red blood cells and the surrounding static tissue. Semi-quantitative techniques provide a more accurate analysis of blood flow dynamics by accounting for the effect of static scattering on spatiotemporal parameters. Quantitative LSI such as optical speckle image velocimetry provides quantitative flow velocity measurements, which is inspired by the particle image velocimetry in fluid mechanics. Additionally, discussions regarding the prospects of future innovations in LSI techniques for optimizing the vascular flow quantification with associated clinical outlook are presented.

Blood Flow Simulation of Aneurysmatic and Sane Thoracic Aorta Using OpenFOAM CFD Software

Cardiovascular diseases still represent one of the most deadly pathologies worldwide. Knowledge of the blood flow dynamics within the cardio-vascular system is crucial in preventing these diseases and analysing their physiology and physio-pathology. CFD simulations are highly effective in guiding clinical predictions and, more importantly, allow the evaluation of physical and clinical parameters that are difficult to measure with common diagnostic techniques. Therefore, in particular, this study is focused on investigating the hemodynamics of the thoracic aorta. Real aortic geometries regarding a sane and diseased patient presenting an aneurysm were considered. CFD simulations were performed with the OpenFOAM C++ library using patient-specific pulsatile blood flow waveforms and implementing the Windkessel pressure boundary condition for the artery outflow. The adopted methodology was preliminarily verified for assessing the numerical uncertainty and convergence. Then, the CFD results were evaluated against experimental data concerning pressure and velocity of the thoracic aorta measured with standard diagnostic techniques. The normal aorta’s blood flow was also compared against the pattern regarding the patient-specific aortic aneurysm. Parameters such as wall pressure, wall shear stress (WSS) and velocity distribution were investigated and discussed. The research highlighted that the blood flow in the aorta is strongly affected by the aneurysm onset, with the growth of recirculation zones being potentially hazardous. The outcomes of the investigation finally demonstrate how CFD simulation tools, capturing the detailed physics of the aortic flow, are powerful tools for supporting clinical activities of the cardio-vascular system.

4D Flow Patterns and Relative Pressure Distribution in a Left Ventricle Model by Shake-the-Box and Proper Orthogonal Decomposition Analysis

PurposeIntraventricular blood flow dynamics are associated with cardiac function. Accurate, noninvasive, and easy assessments of hemodynamic quantities (such as velocity, vortex, and pressure) could be an important addition to the clinical diagnosis and treatment of heart diseases. However, the complex time-varying flow brings many challenges to the existing noninvasive image-based hemodynamic assessments. The development of reliable techniques and analysis tools is essential for the application of hemodynamic biomarkers in clinical practice.MethodsIn this study, a time-resolved particle tracking method, Shake-the-Box, was applied to reconstruct the flow in a realistic left ventricle (LV) silicone model with biological valves. Based on the obtained velocity, 4D pressure field was calculated using a Poisson equation-based pressure solver. Furthermore, flow analysis by proper orthogonal decomposition (POD) of the 4D velocity field has been performed.ResultsAs a result of the Shake-the-Box algorithm, we have extracted: (i) particle positions, (ii) particle tracks, and finally, (iii) 4D velocity fields. From the latter, the temporal evolution of the 3D pressure field during the full cardiac cycle was obtained. The obtained maximal pressure difference extracted along the base-to-apex was about 2.7 mmHg, which is in good agreement with those reported in vivo. The POD analysis results showed a clear picture of different scale of vortices in the pulsatile LV flow, together with their time-varying information and corresponding kinetic energy content. To reconstruct 95% of the kinetic energy of the LV flow, only the first six POD modes would be required, leading to significant data reduction.ConclusionsThis work demonstrated Shake-the-Box is a promising technique to accurately reconstruct the left ventricle flow field in vitro. The good spatial and temporal resolutions of the velocity measurements enabled a 4D reconstruction of the pressure field in the left ventricle. The application of POD analysis showed its potential in reducing the complexity of the high-resolution left ventricle flow measurements. For future work, image analysis, multi-modality flow assessments, and the development of new flow-derived biomarkers can benefit from fast and data-reducing POD analysis.