MODELING OF COMBINED TWIST AND BENDING DEFORMATIONS OF THE FEMOROPOPLITEAL ARTERY

modeling of combined twist and bending deformations of the Femoropopliteal Artery Authors: Ali Ahmadi, Anastasia Desyatova Peripheral arterial disease (PAD) is a narrowing or blockage of the femoropopliteal artery (FPA), leading to reduced blood flow to the downstream tissues. PAD is recognized as one of the most financially demanding vascular disorders to manage, primarily due to the high frequency of reconstruction failures that necessitate subsequent interventions. One of the reasons for the high incidence of PAD and poor treatment results can be attributed to the complex mechanical deformations that FPA experiences during routine activities. The high intramural stresses and strains that can result from severe deformations of the FPA may contribute to arterial injury and the development of diseases or restenosis following treatment. The combined impact of twisting and bending on the stresses experienced by the FPA is not fully understood so far. In the current study, a model with combined limb-flextion induced deformations was developed using flexible rings to apply twist in addition to a guiding catheter and surrounding tissues to apply bending and compression. The current computational model accurately simulated the combined deformations of the FPA that occur during the acute bent leg position. We found that the areas of strain concentration generated by bending deformations were non-uniform. Specifically, regions exhibiting acute kinks, i.e., close to the Adductor Hiatus (AH) and the popliteal artery (PA) below the knee, harbor intense stresses and strains. Furthermore, these regions are highly prone to the development of atherosclerotic disease, which implies a plausible association between elevated strains and intramural stresses, and the pathogenesis of atherosclerotic disease in the FPA. ACKNOWLEDGEMENTS This work was supported by the UNO Student Research and Creative Activity Fair

Development of a methodology for calculating carbon units of heterogeneous territories based on machine learning

The paper describes a methodology for calculating carbon units of heterogeneous territories based on machine learning. The hierarchical structure of areal territories and the structure of the interconnection of of various scales images are described. The approach for identifying and classifying terrain objects for more accurately calculation of the carbon stock of the territory is presented

MECHANICAL STRESSES ASSOCIATED WITH FLATTENING OF HUMAN FEMOROPOPLITEAL ARTERY SPECIMENS DURING PLANAR BIAXIAL TESTING AND THEIR EFFECTS ON THE CALCULATED PHYSIOLOGIC STRESS-STRETCH STATE

Planar biaxial testing is commonly used to characterize the mechanical properties of arteries, but stresses associated with specimen flattening during this test are unknown. We quantified flattening effects in human femoropopliteal arteries (FPAs) of different ages, and determined how they affect the calculated arterial physiologic stress-stretch state. Human FPAs from 472 tissue donors (age 12-82 years, mean 53±16 years) were tested using planar biaxial extension, and morphometric and mechanical characteristics were used to assess the flattening effects. Constitutive parameters for the invariant-based model were adjusted to account for specimen flattening, and used to calculate the physiologic stresses, stretches, axial force, circumferential stiffness, and stored energy for the FPAs in 7 age groups. Flattened specimens were overall 12±4% stiffer longitudinally and 19±11% stiffer circumferentially when biaxially tested. Differences between the stress-stretch curves adjusted and non-adjusted for the effects of flattening were relatively constant across all age groups longitudinally, but increased with age circumferentially. In all age groups these differences were smaller than the intersubject variability. Physiologic stresses, stretches, axial force, circumferential stiffness, and stored energy were all qualitatively and quantitatively similar when calculated with and without the flattening effects. Stresses, stretches, axial force, and stored energy reduced with age, but circumferential stiffness remained relatively constant between 25 and 65 years of age suggesting a homeostatic target of 0.75±0.02 MPa. Flattening effects associated with planar biaxial testing are smaller than the intersubject variability, and have little influence on the calculated physiologic stress-stretch state of human FPAs

The role of editor in the creation of landing page

Статья посвящена изучению явления посадочных страниц как сервисов, организующих и направляющих человеческую деятельность, а также роли редактора в их создании. Выявлены основные структурные элементы «страниц». Особое внимание уделено обязанностям редактора вебсайта.The article is devoted to the study of the phenomenon of landing pages as the services that organize and direct human activity, as well as the role of the editor in their creation. The basic structural elements of "pages" are revealed. Special attention is paid to duties of the editor of the website

In vivo three-dimensional blood velocity profile shapes in the human common, internal, and external carotid arteries

Objective: True understanding of carotid bifurcation pathophysiology requires a detailed knowledge of the hemodynamic conditions within the arteries. Data on carotid artery hemodynamics are usually based on simplified, computer-based, or in vitro experimental models, most of which assume that the velocity profiles are axially symmetric away from the carotid bulb. Modeling accuracy and, more importantly, our understanding of the pathophysiology of carotid bifurcation disease could be considerably improved by more precise knowledge of the in vivo flow properties within the human carotid artery. The purpose of this work was to determine the three-dimensional pulsatile velocity profiles of human carotid arteries. Methods: Flow velocities were measured over the cardiac cycle using duplex ultrasonography, before and after endarterectomy, in the surgically exposed common (CCA), internal (ICA), and external (ECA) carotid arteries (n = 16) proximal and distal to the stenosis/endarterectomy zone. These measurements were linked to a standardized grid across the flow lumina of the CCA, ICA, and ECA. The individual velocities were then used to build mean three-dimensional pulsatile velocity profiles for each of the carotid artery branches. Results: Pulsatile velocity profiles in all arteries were asymmetric about the arterial centerline. Posterior velocities were higher than anterior velocities in all arteries. In the CCA and ECA, velocities were higher laterally, while in the ICA, velocities were higher medially. Pre- and postendarterectomy velocity profiles were significantly different. After endarterectomy, velocity values increased in the common and internal and decreased in the external carotid artery. Conclusions: The in vivo hemodynamics of the human carotid artery are different from those used in most current computer-based and in vitro models. The new information on three-dimensional blood velocity profiles can be used to design models that more closely replicate the actual hemodynamic conditions within the carotid bifurcation. Such models can be used to further improve our understanding of the pathophysiologic processes leading to stroke and for the rational design of medical and interventional therapies

МОДИФИКАЦИЯ СПОСОБА И АЛГОРИТМА КОНТРОЛЯ ИНЕРТНОСТИ ГАЗОХРОМАТОГРАФИЧЕСКИХ СИСТЕМ

The previously proposed approach for controlling the inertness of gas chroma­to­graphic (GC) systems was based on the determination of peak area ratios for polar and non-polar constituents of test-solutions (Srel = Spolar/Snon-polar) for the series of samples obtained by the consequent dilutions (for the 10-times dilutions the number of samp­les was five). This appro­ach was modified with the purpose of increasing the relia­bi­lity of evaluating the minimal quantities of analytes (mlim), for which one can neglect the insufficient inertness of GC systems. In addition to that, the simplification of experimental opera­tions and minimizing the number of parallel determina­ti­ons as well as more rational algorithm of data processing was achieved. The essence of the modified appro­ach was the approximation of Srel = f(pm) data sets with the 3rd degree polynomials, following by comparing these data with the averaged Srel (with standard deviations) values for the most reproducible Srel values of three test-so­lu­tions with the highest concentrations of test-compounds. It was shown that the limits of the inertness for the WCOT-column (with the standard non-polar polydimethylsiloxane stationary phase) were from the fractions of nano­gram to several nanograms of polar analytes in the chromatographic zone. The results for the test-samples contained some polar constituents (e.g., benzyl alco­hol) which lead to suggesting that the integral manifestations of the insufficient inertness could be caused not only by the influence of chromatographic systems, but also by the sorp­tion of polar analytes on the surfaces of vials used for the dilution of test-samples. The differences in mlim values for the same polar components at the same analytical conditions, when the dilutions were carried out in the glass or polypropylene vials, were revealed.Keywords: Gas chromatography, inertness control for chromatographic systems, mixtures of polar and non-polar analytes, consequent dilutions of test-solutions, insufficient inertness of sample preparation  DOI: http://dx.doi.org/10.15826/analitika.2020.24.2.004Igor G. Zenkevich,   Alena I. Desyatova St. Petersburg State University, Institute for ChemistryUniversitetskii prosp., 26, St. Petersburg 198504, Russian FederationРанее предложенный способ контроля инертности газохроматографических систем, основанный на определении отношений площадей пиков полярных и неполярных компонентов тест-растворов (Sотн = Sполярн/Sнеполярн) для серий их по­следовательных разбав­лений (при разбав­лениях в 10 раз их число равно пяти), модифицирован с целями по­лучения более надежных оце­нок минимальных количеств полярных анали­тов (mпред), для кото­рых можно пренебречь недостаточной инертностью си­с­тем. Кроме того, достиг­нуто упрощение эксперимен­та­льных операций, со­кращение числа парал­лельных определений, а также реализован более ра­циональный алго­ритм вычислений на стадии обработки данных. Суть модифицированного алго­ритма состоит в ап­про­к­симации наборов экспериментальных значений Sотн = f(pm) полино­ма­ми третьей степени и сравнении значений Sотн со сред­ни­ми величинами для наиболее воспроизводимых значений Sотн трех рас­т­во­ров с наи­боль­­ши­ми концентрациями тест-компонентов. Показано, что границы инертности WCOT-колонки (со стан­дартной не­по­лярной полидиметилсилоксановой неподвижной фазой) по раз­­ным сое­ди­­нениям составля­ют от долей нанограмма до нескольких нано­грам­мов по­лярных аналитов в хроматографической зоне. Результаты ана­лиза тест-образцов, содержащих некоторые полярные компо­нен­ты (например, бен­­зи­ловый спирт), позволяют предпо­ло­жить, что интегральные проявле­ния не­доста­точ­­ной инертности могут быть обуслов­лены не только влияни­ем хро­ма­т­ографических систем, но и сорбцией полярных аналитов на по­вер­х­­но­с­ти емкостей, используемых для приготовления разбавленных тест-раство­ров. Выявлены различия в значения mпред для од­них и тех же поляр­ных ком­­понентов при одинаковых условиях анализа, если разбавления тест-об­раз­цов про­водят в стеклянных или полипропиленовых емкостях.Ключевые слова: газовая хроматография, контроль инертности хромато­гра­фи­ческих систем, смеси полярных и неполярных аналитов, последова­тельные разбав­ле­ния тест-растворов, недостаточная инертность стадии под­готовки пробDOI: http://dx.doi.org/10.15826/analitika.2020.24.2.00

The choice of a constitutive formulation for modeling limb flexion-induced deformations and stresses in the human femoropopliteal arteries of different ages

Open and endovascular treatments for peripheral arterial disease are notorious for high failure rates. Severe mechanical deformations experienced by the femoropopliteal artery (FPA) during limb flexion and interactions between the artery and repair materials play important roles and may contribute to poor clinical outcomes. Computational modeling can help optimize FPA repair, but these simulations heavily depend on the choice of constitutive model describing the arterial behavior. In this study finite element model of the FPA in the standing (straight) and gardening (acutely bent) postures was built using computed tomography data, longitudinal pre-stretch and biaxially determined mechanical properties. Springs and dashpots were used to represent surrounding tissue forces associated with limb flexion-induced deformations. These forces were then used with age-specific longitudinal pre-stretch and mechanical properties to obtain deformed FPA configurations for seven age groups. Four commonly used invariant-based constitutive models were compared to determine the accuracy of capturing deformations and stresses in each age group. The four-fiber FPA model most accurately portrayed arterial behavior in all ages, but in subjects younger than 40 years, the performance of all constitutive formulations was similar. In older subjects, Demiray (Delfino) and classic two-fiber Holzapfel–Gasser–Ogden formulations were better than the Neo-Hookean model for predicting deformations due to limb flexion, but both significantly overestimated principal stresses compared to the FPA or Neo-Hookean models

In situ longitudinal pre-stretch in the human femoropopliteal artery

In situ longitudinal (axial) pre-stretch (LPS) plays a fundamental role in the mechanics of the femoropopliteal artery (FPA). It conserves energy during pulsation and prevents buckling of the artery during limb movement. We investigated how LPS is affected by demographics and risk factors, and how these patient characteristics associate with the structural and physiologic features of the FPA. LPS was measured in n = 148 fresh human FPAs (14–80 years old). Mechanical properties were characterized with biaxial extension and histopathological characteristics were quantified with Verhoeff–Van Gieson Staining. Constitutive modeling was used to calculate physiological stresses and stretches which were then analyzed in the context of demographics, risk factors and structural characteristics. Age had the strongest negative effect (r = −0.812, p \u3c 0.01) on LPS and could alone explain 66% of LPS variability. Male gender, higher body mass index, hypertension, diabetes, coronary artery disease, dyslipidemia and tobacco use had negative effects on LPS, but only the effect of tobacco was not associated with aging. FPAs with less pre-stretch had thicker medial layers, but thinner intramural elastic fibers with less dense and more fragmented external elastic laminae. Elastin degradation was associated with decreased physiological tethering force and longitudinal stress, while circumferential stress remained constant. FPA wall pathology was negatively associated with LPS (r = −0.553, p \u3c 0.01), but the effect was due primarily to aging. LPS in the FPA may serve as an energy reserve for adaptive remodeling. Reduction of LPS due to degradation and fragmentation of intramural longitudinal elastin during aging can be accelerated in tobacco users

Non-Destructive Characterization of Peripheral Arteries using Intravascular Ultrasound

Peripheral Artery Disease (PAD) is the chronic obstruction of blood flow to the extremities caused by plaque buildup. Poor circulation results in exertional pain, numbness, and weakness, and in severe cases, can manifest critical conditions, including gangrene and limb loss. PAD affects approximately 8.5 million Americans and costs the United States $21 billion annually in direct medical expenses. High expenditures are attributed to operation and intervention failures resulting in frequent need for revascularization. Treatment of PAD typically involves lifestyle/diet adjustments, bypass surgery, or angioplasty/stenting. Unfortunately, repeated limb deformation during locomotion often results in adverse repair device-artery interactions, which hinder the long-term efficacy of endovascular therapies. Patient and lesion-specific device selection guided by computational modeling can help improve clinical outcomes, but these models rely heavily on accurately recorded three-dimensional arterial geometry and plaque composition. Intravascular ultrasound (IVUS) is a minimally invasive method of endovascular imaging that allows evaluation of the geometry and composition of the arterial wall, but its two-dimensional nature is often insufficient to capture complex three-dimensional plaques. We have developed a method of obtaining three-dimensional arterial geometry from two-dimensional IVUS images to build Computer-Aided Design models of calcified human femoropopliteal arteries. Our imaging method will allow for the characterization of calcium, necrotic core, fibrofatty, and fibrous tissue using IVUS. Correlation of IVUS images with conventional histology, micro-CT imaging, and clinical CTA data will help inform computational models.https://digitalcommons.unmc.edu/surp2021/1025/thumbnail.jp

In situ longitudinal pre-stretch in the human femoropopliteal artery

In situ longitudinal (axial) pre-stretch (LPS) plays a fundamental role in the mechanics of the femoropopliteal artery (FPA). It conserves energy during pulsation and prevents buckling of the artery during limb movement. We investigated how LPS is affected by demographics and risk factors, and how these patient characteristics associate with the structural and physiologic features of the FPA. LPS was measured in n = 148 fresh human FPAs (14–80 years old). Mechanical properties were characterized with biaxial extension and histopathological characteristics were quantified with Verhoeff–Van Gieson Staining. Constitutive modeling was used to calculate physiological stresses and stretches which were then analyzed in the context of demographics, risk factors and structural characteristics. Age had the strongest negative effect (r = −0.812, p \u3c 0.01) on LPS and could alone explain 66% of LPS variability. Male gender, higher body mass index, hypertension, diabetes, coronary artery disease, dyslipidemia and tobacco use had negative effects on LPS, but only the effect of tobacco was not associated with aging. FPAs with less pre-stretch had thicker medial layers, but thinner intramural elastic fibers with less dense and more fragmented external elastic laminae. Elastin degradation was associated with decreased physiological tethering force and longitudinal stress, while circumferential stress remained constant. FPA wall pathology was negatively associated with LPS (r = −0.553, p \u3c 0.01), but the effect was due primarily to aging. LPS in the FPA may serve as an energy reserve for adaptive remodeling. Reduction of LPS due to degradation and fragmentation of intramural longitudinal elastin during aging can be accelerated in tobacco users