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1.
Vasc Endovascular Surg ; 54(1): 5-11, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31506033

RESUMO

INTRODUCTION: High flow rates may develop in arteriovenous fistula (AVF), resulting in clinical syndromes of steal, aneurysmal fistula, or high-output cardiac failure. Various techniques with varying success have been advocated to treat this difficult problem. We present a hemodynamically validated novel banding technique. METHODS: We designed a computational fluid dynamic (CFD) model of the native high-flow AVF and tested various juxta-anastomotic venous diameters to determine the effect on AVF blood flow and pressure. We translated this principle in our banding technique, wherein adjustable banding was performed in conjunction with ultrasound-guided brachial artery flow measurement to determine the optimal band diameter. Polyurethane patch was used to fashion the adjustable band. Patient demographics, AVF flow parameters pre- and postintervention, operative intervention, and ultrasound follow-up data were collected prospectively. RESULTS: Our CFD testing demonstrated that the band diameter needed to achieve optimal distal blood pressure and preserve AVF flow depending on blood pressure, end capillary pressure, venous pressure, and vascular diameters. Five patients subsequently underwent dynamic banding of symptomatic high-flow AVF. Mean brachial artery blood flow rates pre- and postbanding were 2964 mL/min (confidence interval [CI]: 1487-4440 mL/min) and 1099 mL/min (CI: 571.7-1627 mL/min), respectively (P = .01). All patients had symptomatic improvement, and at a mean follow-up of 1 year, this benefit was sustained with no AVF thrombosis or loss. CONCLUSION: Adjustable dynamic band using ultrasound-guided brachial artery flow shows promising results in producing accurate AVF blood flow reduction with sustained efficacy in the short term for patients with symptomatic high-flow AVF.


Assuntos
Derivação Arteriovenosa Cirúrgica/efeitos adversos , Artéria Braquial/fisiopatologia , Hemodinâmica , Complicações Pós-Operatórias/cirurgia , Diálise Renal , Adolescente , Idoso , Idoso de 80 Anos ou mais , Velocidade do Fluxo Sanguíneo , Artéria Braquial/diagnóstico por imagem , Simulação por Computador , Humanos , Ligadura , Pessoa de Meia-Idade , Modelos Cardiovasculares , Complicações Pós-Operatórias/diagnóstico por imagem , Complicações Pós-Operatórias/fisiopatologia , Estudos Prospectivos , Fluxo Sanguíneo Regional , Reoperação , Fatores de Tempo , Resultado do Tratamento , Ultrassonografia de Intervenção
2.
Phys Rev Lett ; 123(21): 218101, 2019 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-31809131

RESUMO

We develop an iterated map model to describe the bifurcations and complex dynamics caused by the feedback between voltage and intracellular Ca^{2+} and Na^{+} concentrations in paced ventricular myocytes. Voltage and Ca^{2+} can form either a positive or a negative feedback loop, while voltage and Na^{+} form a negative feedback loop. Under certain diseased conditions, when the feedback between voltage and Ca^{2+} is positive, Hopf bifurcations occur, leading to periodic oscillatory behaviors. When this feedback is negative, period-doubling bifurcation routes to alternans and chaos occur.


Assuntos
Cálcio/metabolismo , Modelos Cardiovasculares , Miócitos Cardíacos/metabolismo , Sódio/metabolismo , Relógios Biológicos , Cátions Bivalentes/metabolismo , Cátions Monovalentes/metabolismo , Membrana Celular/metabolismo , Polaridade Celular , Retroalimentação Fisiológica , Ventrículos do Coração/citologia , Ventrículos do Coração/metabolismo , Potenciais da Membrana , Miócitos Cardíacos/citologia , Trocador de Sódio e Cálcio/metabolismo
3.
Phys Rev Lett ; 123(22): 228103, 2019 Nov 29.
Artigo em Inglês | MEDLINE | ID: mdl-31868401

RESUMO

Neuronal activity induces changes in blood flow by locally dilating vessels in the brain microvasculature. How can the local dilation of a single vessel increase flow-based metabolite supply, given that flows are globally coupled within microvasculature? Solving the supply dynamics for rat brain microvasculature, we find one parameter regime to dominate physiologically. This regime allows for robust increase in supply independent of the position in the network, which we explain analytically. We show that local coupling of vessels promotes spatially correlated increased supply by dilation.


Assuntos
Encéfalo/irrigação sanguínea , Microvasos/fisiologia , Modelos Cardiovasculares , Animais , Encéfalo/metabolismo , Microcirculação/fisiologia , Microvasos/inervação , Microvasos/metabolismo , Neurônios/fisiologia , Ratos
4.
J Vasc Res ; 56(6): 296-307, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31671424

RESUMO

In this study, using fluid-structure interaction (FSI), 3-dimensional blood flow in an aneurysm in the circle of Willis - which is located in the middle cerebral artery (MCA) - has been simulated. The purpose of this study is to evaluate the effect of a partly blocked vessel on an aneurysm. To achieve this purpose, two cases have been investigated using the FSI method: in the first case, an ideal geometry of aneurysm in the MCA has been simulated; in the second case, modeling is performed for an ideal geometry of the aneurysm in the MCA with a partly blocked vessel. All boundary conditions, properties and modeling methods were considered the same for both cases. The only difference between the two cases was that part of the MCA parent artery was blocked in the second case. In order to consider the hyperelastic property of the wall and the non-Newtonian properties of the blood, the Mooney-Rivlin model and the Carreau model have been used, respectively. In the second case, the Von Mises stress in the peak systole is 26% higher than in the first case. With regard to the high amount of Von Mises stress, the risk of rupture of the aneurysm is higher in this case. In the second case, the maximum wall shear stress (WSS) is 12% higher than in the first case. And maximum displacement in the second case is also higher than in the first. So, the risk of growth of the aneurysm is higher in cases with a partly blocked vessel.


Assuntos
Circulação Cerebrovascular , Círculo Arterial do Cérebro/fisiopatologia , Simulação por Computador , Infarto da Artéria Cerebral Média/fisiopatologia , Aneurisma Intracraniano/fisiopatologia , Modelos Cardiovasculares , Idoso , Velocidade do Fluxo Sanguíneo , Angiografia Cerebral/métodos , Círculo Arterial do Cérebro/diagnóstico por imagem , Angiografia por Tomografia Computadorizada , Progressão da Doença , Feminino , Humanos , Aneurisma Intracraniano/diagnóstico por imagem , Fluxo Sanguíneo Regional
5.
Angiol Sosud Khir ; 25(3): 107-112, 2019.
Artigo em Russo | MEDLINE | ID: mdl-31503254

RESUMO

Computer-aided simulation appropriately using the method of computational fluid dynamics (CFD) makes it possible to determine the elevated-risk zones of most probable formation of restenosis. The main idea of the method described in our article consists in a possibility of creating by the model of the geometrical shape of the vessel and characteristics of the flow at inlets and outlets the parameters of flow in each point of a vessel. The curves of velocity are used to create the curves of pressure at inlets and outlets, which are used in a CFD model. The resulting from CFD simulation of blood flow are nonstationary three-dimensional fields of pressure and velocity in the area under study. Visual examination of the dynamics of these fields makes it possible to judge about possible problem zones inside the area of flow and on the internal wall of the vessel. This article also presents a clinical case report illustrating the use of this technique.


Assuntos
Artérias Carótidas , Endarterectomia das Carótidas , Velocidade do Fluxo Sanguíneo , Artérias Carótidas/fisiopatologia , Hemodinâmica , Humanos , Modelos Cardiovasculares
6.
PLoS Comput Biol ; 15(8): e1007259, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-31415554

RESUMO

Recent developments in cardiovascular modelling allow us to simulate blood flow in an entire human body. Such model can also be used to create databases of virtual subjects, with sizes limited only by computational resources. In this work, we study if it is possible to estimate cardiovascular health indices using machine learning approaches. In particular, we carry out theoretical assessment of estimating aortic pulse wave velocity, diastolic and systolic blood pressure and stroke volume using pulse transit/arrival timings derived from photopletyshmography signals. For predictions, we train Gaussian process regression using a database of virtual subjects generated with a cardiovascular simulator. Simulated results provides theoretical assessment of accuracy for predictions of the health indices. For instance, aortic pulse wave velocity can be estimated with a high accuracy (r > 0.9) when photopletyshmography is measured from left carotid artery using a combination of foot-to-foot pulse transmit time and peak location derived for the predictions. Similar accuracy can be reached for diastolic blood pressure, but predictions of systolic blood pressure are less accurate (r > 0.75) and the stroke volume predictions are mostly contributed by heart rate.


Assuntos
Pressão Sanguínea , Modelos Cardiovasculares , Análise de Onda de Pulso/estatística & dados numéricos , Aorta/fisiologia , Velocidade do Fluxo Sanguíneo/fisiologia , Pressão Sanguínea/fisiologia , Biologia Computacional , Simulação por Computador , Bases de Dados Factuais , Humanos , Aprendizado de Máquina , Distribuição Normal , Fotopletismografia/estatística & dados numéricos , Volume Sistólico/fisiologia , Interface Usuário-Computador , Rigidez Vascular , Dispositivos Eletrônicos Vestíveis/estatística & dados numéricos
7.
Nanoscale ; 11(33): 15537-15549, 2019 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-31393488

RESUMO

Inhaled atmospheric nanoparticles (ANPs) can migrate into human blood vessels. However, the exact pathogenesis has not yet been well elucidated. In this study, a perfusable 3D human microvessel network was constructed in a microfluidic device. This functional 3D micro-tissue partly mimicked the physiological response of human vessels. Intravascular nanoparticles tend to adsorb proteins to form a protein corona. Based on this pathological response, vessel permeability and vasoconstriction resulting from ANP stimulation might be related to vascular inflammation. It mediated abnormal expression of nuclear factor-κB (NF-κB) and an influx of intracellular Ca2+ ([Ca2+]i). This biological behavior disturbed the normal expression of intercellular cell adhesion molecule 1 (ICAM-1) and vascular endothelial growth factor (VEGF). The imbalance of nitric oxide (NO) and endothelin-1 (ET-1) further resulted in endothelial cell contraction. All these bio-events induced the loss of tight junctions (ZO-1) which enhanced vessel permeability. Meanwhile, ANP induced-vascular toxicity was also found in mice. Our observations provide a plausible explanation for how the ANPs affect human vascular function. The vessel-on-chip provides a bridge between in vitro results and human responses. We aimed to use this human 3D functional microvascular model to mimic the physiological responses of human vessels. This model is suitable for the evaluation of vascular toxicity after the human vessel exposure to ANPs.


Assuntos
Dispositivos Lab-On-A-Chip , Microvasos/química , Modelos Cardiovasculares , Nanopartículas/química , Animais , Cálcio/metabolismo , Técnicas de Cultura de Células , Células Endoteliais da Veia Umbilical Humana , Humanos , Molécula 1 de Adesão Intercelular/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Microscopia Confocal , Microvasos/patologia , NF-kappa B/metabolismo , Óxido Nítrico/metabolismo , Coroa de Proteína/química , Engenharia Tecidual , Fator A de Crescimento do Endotélio Vascular/metabolismo , Proteína da Zônula de Oclusão-1/metabolismo
8.
PLoS Comput Biol ; 15(8): e1007260, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-31393876

RESUMO

Spontaneous sub-cellular calcium release events (SCRE) are conjectured to promote rapid arrhythmias associated with conditions such as heart failure and atrial fibrillation: they can underlie the emergence of spontaneous action potentials in single cells which can lead to arrhythmogenic triggers in tissue. The multi-scale mechanisms of the development of SCRE into arrhythmia triggers, and their dynamic interaction with the tissue substrate, remain elusive; rigorous and simultaneous study of dynamics from the nanometre to the centimetre scale is a major challenge. The aim of this study was to develop a computational approach to overcome this challenge and study potential bi-directional coupling between sub-cellular and tissue-scale arrhythmia phenomena. A framework comprising a hierarchy of computational models was developed, which includes detailed single-cell models describing spatio-temporal calcium dynamics in 3D, efficient non-spatial cell models, and both idealised and realistic tissue models. A phenomenological approach was implemented to reproduce SCRE morphology and variability in the efficient cell models, comprising the definition of analytical Spontaneous Release Functions (SRF) whose parameters may be randomly sampled from appropriate distributions in order to match either the 3D cell models or experimental data. Pro-arrhythmogenic pacing protocols were applied to initiate re-entry and promote calcium overload, leading to the emergence of SCRE. The SRF accurately reproduced the dynamics of SCRE and its dependence on environment variables under multiple different conditions. Sustained re-entrant excitation promoted calcium overload, and led to the emergence of focal excitations after termination. A purely functional mechanism of re-entry and focal activity localisation was demonstrated, related to the unexcited spiral wave core. In conclusion, a novel approach has been developed to dynamically model SCRE at the tissue scale, which facilitates novel, detailed multi-scale mechanistic analysis. It was revealed that complex re-entrant excitation patterns and SCRE may be bi-directionally coupled, promoting novel mechanisms of arrhythmia perpetuation.


Assuntos
Arritmias Cardíacas/fisiopatologia , Sinalização do Cálcio/fisiologia , Modelos Cardiovasculares , Potenciais de Ação/fisiologia , Algoritmos , Arritmias Cardíacas/etiologia , Fibrilação Atrial/fisiopatologia , Biologia Computacional , Simulação por Computador , Insuficiência Cardíaca/fisiopatologia , Humanos , Imagem Tridimensional , Análise de Célula Única/estatística & dados numéricos , Processos Estocásticos
9.
Chaos ; 29(7): 073102, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31370420

RESUMO

Mathematical models describing the dynamics of the cardiac action potential are of great value for understanding how changes to the system can disrupt the normal electrical activity of cells and tissue in the heart. However, to represent specific data, these models must be parameterized, and adjustment of the maximum conductances of the individual contributing ionic currents is a commonly used method. Here, we present a method for investigating the uniqueness of such resulting parameterizations. Our key question is: Can the maximum conductances of a model be changed without giving any appreciable changes in the action potential? If so, the model parameters are not unique and this poses a major problem in using the models to identify changes in parameters from data, for instance, to evaluate potential drug effects. We propose a method for evaluating this uniqueness, founded on the singular value decomposition of a matrix consisting of the individual ionic currents. Small singular values of this matrix signify lack of parameter uniqueness and we show that the conclusion from linear analysis of the matrix carries over to provide insight into the uniqueness of the parameters in the nonlinear case. Using numerical experiments, we quantify the identifiability of the maximum conductances of well-known models of the cardiac action potential. Furthermore, we show how the identifiability depends on the time step used in the observation of the currents, how the application of drugs may change identifiability, and, finally, how the stimulation protocol can be used to improve the identifiability of a model.


Assuntos
Potenciais de Ação/fisiologia , Simulação por Computador , Coração/fisiologia , Modelos Cardiovasculares , Humanos
10.
Comput Methods Biomech Biomed Engin ; 22(15): 1174-1185, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31423837

RESUMO

Prestretch is observed in many soft biological tissues, directly influencing the mechanical behavior of the tissue in question. The development of this prestretch occurs through complex growth and remodeling phenomena, which yet remain to be elucidated. In the present study it was investigated whether local cell-mediated traction forces can explain the development of global anisotropic tissue prestretch in the mitral valve. Towards this end, a model predicting actin stress fiber-generated traction forces was implemented in a finite element framework of the mitral valve. The overall predicted magnitude of prestretch induced valvular contraction after release of in vivo boundary constraints was in good agreement with data reported on valvular retraction after excision from the heart. Next, by using a systematic variation of model parameters and structural properties, a more anisotropic prestretch development in the valve could be obtained, which was also similar to physiological values. In conclusion, this study shows that cell-generated traction forces could explain prestretch magnitude and anisotropy in the mitral valve.


Assuntos
Valva Mitral/fisiopatologia , Modelos Cardiovasculares , Estresse Mecânico , Anisotropia , Fenômenos Biomecânicos , Simulação por Computador , Elasticidade , Análise de Elementos Finitos
11.
Sheng Wu Yi Xue Gong Cheng Xue Za Zhi ; 36(4): 649-656, 2019 Aug 25.
Artigo em Chinês | MEDLINE | ID: mdl-31441267

RESUMO

Based on the noninvasive detection indeices and fuzzy mathematics method, this paper studied the noninvasive, convenient and economical cardiovascular health assessment system. The health evaluation index of cardiovascular function was built based on the internationally recognized risk factors of cardiovascular disease and the noninvasive detection index. The weight of 12 indexes was completed by the analytic hierarchy process, and the consistency test was passed. The membership function, evaluation matrix and evaluation model were built by fuzzy mathematics. The introducted methods enhanced the scientificity of the evaluation system. Through the Kappa consistency test, McNemer statistical results ( P = 0.995 > 0.05) and Kappa values (Kappa = 0.616, P < 0.001) suggest that the comprehensive evaluation results of model in this paper are relatively consistent with the clinical, which is of certain scientific significance for the early detection of cardiovascular diseases.


Assuntos
Doenças Cardiovasculares/diagnóstico , Sistema Cardiovascular , Lógica Fuzzy , Modelos Cardiovasculares , Humanos , Pesquisa
12.
Comput Methods Biomech Biomed Engin ; 22(15): 1197-1208, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31432696

RESUMO

Despite the general interest in aneurysm rupture prediction, the aneurysm formation has received limited attention. The goal of this study is to assess whether an aneurysm may be instigated in a healthy model of an aorta inflated by a supra-physiological pressure. The effect of two main aspects on numerical predictions has been explored: i) the geometric design and ii) the constitutive law adopted to represent the material properties. Firstly, higher values of wall stress and displacement magnitude were generated in the physiologic model compared to the cylindrical one when assigning the same material properties. Secondly, greater deformations are observed in the anisotropic model compared to the isotropic one.


Assuntos
Aneurisma/fisiopatologia , Aorta Torácica/fisiopatologia , Análise de Elementos Finitos , Modelos Cardiovasculares , Anisotropia , Fenômenos Biomecânicos , Humanos , Pressão , Estresse Mecânico
13.
J Stroke Cerebrovasc Dis ; 28(11): 104339, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31451338

RESUMO

BACKGROUND: Infarcts in the lateral striate artery (LSA) territory can be caused by several pathological changes, including lipohyalinosis and microatheroma. However, fluid dynamic effects on these changes remain unknown. Thus, we investigated whether the fluid dynamic metrics of the LSAs were altered in patients with acute ischemic stroke using computational fluid dynamics (CFD) analysis. METHODS: Fifty-one patients with acute ischemic stroke confined in the basal ganglia and/or corona radiata underwent high-resolution magnetic resonance angiography (HR-MRA) at 7T. We performed CFD analyses to obtain indices including the wall shear stress (WSS), WSS gradient (WSSG), and flow velocity (FV) and compared these values between the ipsilesional and contralesional sides in the patients with infarcts in the LSA or non-LSA territories. RESULTS: In patients with LSA-territory infarcts, the WSS, WSSG, and FV values were significantly lower in the ipsilesional LSAs than in the contralesional LSAs (P = .01-.03), while these values in the proximal middle cerebral arteries showed no significant lateralities. In contrast, in patients with non-LSA-territory infarcts, there were no significant lateralities in the metrics between the ipsilesional and contralesional sides. CONCLUSIONS: The CFD analyses using HR-MRA revealed significantly low WSS and WSSG values of the ipsilesional LSAs compared with that of the contralesional side in patients with LSA-territory infarcts, suggesting that fluid dynamic factors of LSAs can be one of the risk factors for LSA-territory infarctions.


Assuntos
Isquemia Encefálica/diagnóstico por imagem , Angiografia Cerebral/métodos , Artérias Cerebrais/diagnóstico por imagem , Circulação Cerebrovascular , Angiografia por Ressonância Magnética , Modelos Cardiovasculares , Modelagem Computacional Específica para o Paciente , Acidente Vascular Cerebral/diagnóstico por imagem , Adulto , Idoso , Idoso de 80 Anos ou mais , Velocidade do Fluxo Sanguíneo , Isquemia Encefálica/fisiopatologia , Artérias Cerebrais/fisiopatologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Valor Preditivo dos Testes , Estudos Prospectivos , Estresse Mecânico , Acidente Vascular Cerebral/fisiopatologia
14.
Comput Methods Biomech Biomed Engin ; 22(15): 1229-1238, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31437018

RESUMO

Vortex structures, as one of the most important features of cardiac flow, have a crucial impact on the left ventricle function and pathological conditions. These swirling flows are closely related to the presence of turbulence in left ventricle which is investigated in the current study. Using an extended model of the left heart, including a fluid-structure interaction (FSI) model of the mitral valve with a realistic geometry, the effect of using two numerical turbulent models, k-ε and Spalart-Allmaras (SA), on diastolic flow patterns is studied and compared with results from laminar flow model. As a result of the higher dissipation rate in turbulent models (k-ε and SA), vortices are larger and stronger in the laminar flow model. Comparing E/A ratio in the three models (Laminar, k-ε, and SA) with experimental data from healthy subjects, it is concluded that the results from k-ε model are more accurate.


Assuntos
Simulação por Computador , Circulação Coronária/fisiologia , Modelos Cardiovasculares , Função Ventricular/fisiologia , Velocidade do Fluxo Sanguíneo , Humanos , Valva Mitral/fisiologia , Análise Numérica Assistida por Computador , Pressão , Estresse Mecânico
15.
Adv Physiol Educ ; 43(3): 423-429, 2019 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-31408386

RESUMO

An understanding of the complexity of the cardiovascular system is incomplete without a knowledge of the venous system. It is important for students to understand that, in a closed system, like the circulatory system, changes to the venous side of the circulation have a knock-on effect on heart function and the arterial system and vice versa. Veins are capacitance vessels feeding blood to the right side of the heart. Changes in venous compliance have large effects on the volume of blood entering the heart and hence cardiac output by the Frank-Starling Law. In healthy steady-state conditions, venous return has to equal cardiac output, i.e., the heart cannot pump more blood than is delivered to it. A sound understanding of the venous system is essential in understanding how changes in cardiac output occur with changes in right atrial pressure or central venous pressure, and the effect these changes have on arterial blood pressure regulation. The aim of this paper is to detail simple hands-on physiological assessments that can be easily undertaken in the practical laboratory setting and that illustrate some key functions of veins. Specifically, we illustrate that venous valves prevent the backflow of blood, that venous blood pressure increases from the heart to the feet, that the skeletal muscle pump facilitates venous return, and we investigate the physiological and clinical significance of central venous pressure and how it may be assessed.


Assuntos
Compreensão , Modelos Cardiovasculares , Fisiologia/educação , Veias/fisiologia , Pressão Venosa/fisiologia , Volume Sanguíneo/fisiologia , Débito Cardíaco/fisiologia , Humanos
16.
Vasc Endovascular Surg ; 53(7): 572-582, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31382837

RESUMO

BACKGROUND-AIM: Limited data exist concerning the fluid dynamic changes induced by endovascular aortic repair with fenestrated and chimney graft modalities in pararenal aneurysms. We aimed to investigate and compare the wall shear stress (WSS) and flow dynamics for the branch vessels before and after endovascular aortic repair with fenestrated and chimney techniques. METHODS: Modeling was done for patient specific pararenal aortic aneurysms employing fenestrated and chimney grafts (Materialise Mimics 10.0) before and after the endovascular procedure, using computed tomography scans of patients. Surface and spatial grids were created using the ANSYS CFD meshing software 2019 R2. Assessment of blood flow, streamlines, and WSS before and after aneurysm repair was performed. RESULTS: The endovascular repair with chimney grafts leaded to a 43% to 53% reduction in perfusion in renal arteries. In fenestrated reconstruction, we observed a 15% reduced perfusion in both renal arteries. In both cases, we observed a decrease in the recirculation phenomena of the aorta after endovascular repair. Concerning the grafts of the renal arteries, we observed in both the transverse and longitudinal axes low WSS regions with simultaneous recirculation of the flow 1 cm distal to the ostium sites in both aortic graft models. High WSS regions appeared in the sites of ostium. CONCLUSIONS: We observed reduced renal perfusion in chimney grafts compared to fenestrated grafts, probably caused by the long and kinked characteristics of these devices.


Assuntos
Aneurisma da Aorta Abdominal/cirurgia , Implante de Prótese Vascular/instrumentação , Prótese Vascular , Tomada de Decisão Clínica , Procedimentos Endovasculares/instrumentação , Modelos Cardiovasculares , Modelagem Computacional Específica para o Paciente , Aneurisma da Aorta Abdominal/diagnóstico por imagem , Aneurisma da Aorta Abdominal/fisiopatologia , Aortografia/métodos , Implante de Prótese Vascular/efeitos adversos , Angiografia por Tomografia Computadorizada , Procedimentos Endovasculares/efeitos adversos , Hemodinâmica , Humanos , Hidrodinâmica , Seleção de Pacientes , Complicações Pós-Operatórias/diagnóstico por imagem , Complicações Pós-Operatórias/etiologia , Complicações Pós-Operatórias/fisiopatologia , Valor Preditivo dos Testes , Desenho de Prótese , Interpretação de Imagem Radiográfica Assistida por Computador , Circulação Renal , Estresse Mecânico , Resultado do Tratamento
17.
PLoS Comput Biol ; 15(8): e1007231, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-31469820

RESUMO

Capillaries are the prime location for oxygen and nutrient exchange in all tissues. Despite their fundamental role, our knowledge of perfusion and flow regulation in cortical capillary beds is still limited. Here, we use in vivo measurements and blood flow simulations in anatomically accurate microvascular network to investigate the impact of red blood cells (RBCs) on microvascular flow. Based on these in vivo and in silico experiments, we show that the impact of RBCs leads to a bias toward equating the values of the outflow velocities at divergent capillary bifurcations, for which we coin the term "well-balanced bifurcations". Our simulation results further reveal that hematocrit heterogeneity is directly caused by the RBC dynamics, i.e. by their unequal partitioning at bifurcations and their effect on vessel resistance. These results provide the first in vivo evidence of the impact of RBC dynamics on the flow field in the cortical microvasculature. By structural and functional analyses of our blood flow simulations we show that capillary diameter changes locally alter flow and RBC distribution. A dilation of 10% along a vessel length of 100 µm increases the flow on average by 21% in the dilated vessel downstream a well-balanced bifurcation. The number of RBCs rises on average by 27%. Importantly, RBC up-regulation proves to be more effective the more balanced the outflow velocities at the upstream bifurcation are. Taken together, we conclude that diameter changes at capillary level bear potential to locally change the flow field and the RBC distribution. Moreover, our results suggest that the balancing of outflow velocities contributes to the robustness of perfusion. Based on our in silico results, we anticipate that the bi-phasic nature of blood and small-scale regulations are essential for a well-adjusted oxygen and energy substrate supply.


Assuntos
Encéfalo/irrigação sanguínea , Eritrócitos/fisiologia , Microvasos/fisiologia , Animais , Velocidade do Fluxo Sanguíneo/fisiologia , Capilares/anatomia & histologia , Capilares/fisiologia , Circulação Cerebrovascular/fisiologia , Biologia Computacional , Simulação por Computador , Feminino , Hematócrito , Camundongos , Camundongos Endogâmicos C57BL , Microvasos/anatomia & histologia , Modelos Cardiovasculares , Modelos Neurológicos , Vasodilatação/fisiologia
18.
J Med Eng Technol ; 43(4): 223-234, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31464556

RESUMO

In vitro study plays an important role in the experimental study of cardiovascular dynamics. An essential hardware facility that mimics the blood flow changes and provides the required test conditions, a mock circulatory test rig (MCTR), is imperative for the execution of in vitro study. This paper examines the current MCTRs in use for the testing of artificial cardiovascular organs. Various aspects of the MCTRs are surveyed, including the necessity of in vitro study, the building of MCTRs, relevant standards, general system structure (e.g., the motion and driving, fluid, measurement subsystems), classification, motion driving mechanism of MCTRs, and the considerations for the modelling of the physiological impedance of MCTRs. Examples of the steady and pulsatile flow types of the MCTRs are introduced. Recent developments in MCTRs are inspected and possible future design improvements suggested. This study will help researchers in the design, construction, analysis, and selection of MCTRs for cardiovascular research.


Assuntos
Órgãos Artificiais , Modelos Cardiovasculares , Animais , Desenho de Equipamento , Humanos , Fluxo Pulsátil
19.
Int J Comput Assist Radiol Surg ; 14(10): 1805-1813, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31363984

RESUMO

PURPOSE: Image-based hemodynamic simulations have great potential for precise blood flow predictions in intracranial aneurysms. Due to model assumptions and simplifications with respect to boundary conditions, clinical acceptance remains limited. METHODS: Within this study, we analyzed the influence of outflow-splitting approaches on multiple aneurysm studies and present a new outflow-splitting approach that takes the precise morphological vessel cross sections into account. We provide a detailed comparison of five outflow strategies considering eight intracranial aneurysms: zero-pressure configuration (1), a flow splitting inspired by Murray's law with a square (2) and a cubic (3) vessel diameter, a flow splitting incorporating vessel bifurcations based on circular vessel cross sections (4) and our novel flow splitting including vessel bifurcations and anatomical vessel cross sections (5). Other boundary conditions remain constant. For each simulation and each aneurysm, we conducted an evaluation based on common hemodynamic parameters, e.g., normalized wall shear stress and inflow concentration index. RESULTS: The comparison of five outflow strategies for image-based simulations shows a large variability regarding the parameters of interest. Qualitatively, our strategy based on anatomical cross sections yields a more uniform flow rate distribution with increased aneurysm inflow rates. The commonly used zero-pressure approach shows the largest variations, especially for more distal aneurysms. A rank ordering of multiple aneurysms in one patient might still be possible, since the ordering appeared to be independent of the outflow strategy. CONCLUSIONS: The results reveal that outlet boundary conditions have a crucial impact on image-based blood flow simulations, especially for multiple aneurysm studies. We could confirm the advantages of the more complex outflow-splitting model (4) including an incremental improvement (5) compared to strategies (1), (2) and (3) for this application scenario. Furthermore, we discourage from using zero-pressure configurations that lack a physiological basis.


Assuntos
Circulação Cerebrovascular/fisiologia , Simulação por Computador , Aneurisma Intracraniano/fisiopatologia , Modelos Cardiovasculares , Velocidade do Fluxo Sanguíneo/fisiologia , Hemodinâmica/fisiologia , Humanos , Processamento de Imagem Assistida por Computador/métodos
20.
Int J Cardiovasc Imaging ; 35(12): 2139-2146, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31352559

RESUMO

Percentage diameter stenosis (%DS) by angiography is still commonly used to determine luminal obstruction of coronary artery disease (CAD) lesions. While visual estimation of %DS is widespread, because of high inter-operator variability, quantitative coronary arteriography (QCA) analysis is the gold standard. There are two %DS formulas: %DS1 averages the proximal and distal reference vessel diameter (RVD); %DS2 interpolates the RVD. This study aims to evaluate the difference between %DS assessed by QCA in two datasets, phantom lesion models and CAD patients. Ten phantom lesion models (PLMs) and 354 CAD lesions from the FIRST trial were assessed by QCA. In the latter, two scenarios were assessed: Scenario A (worst view), the most common approach in the clinical setting; and Scenario B (average of two complementary views), the standard core-laboratory analysis. In the PLMs, %DS1 and %DS2 mean ± standard deviation (median) was 58.5 ± 21.7 (61.6) and 58.7 ± 21.6 (61.8), respectively, with a signed difference of - 0.2% ± 0.3% (- 0.1%). In Scenario A, the mean %DS1 was 43.8 ± 9.1 (43.3) and 44.0 ± 9.1 (42 .9) in %DS2. In Scenario B, the mean %DS1 was 45.3 ± 8.8 (45.1) and 45.5 ± 9.0 (45.1) in %DS2. The signed difference was - 0.2% ± 2.4% (0.0%) and - 0.2% ± 2.1% (0.0%) in Scenario A and B, respectively. These differences between formulas ranged from - 1.2 to 0.5% for the phantom cases compared to - 17.7% to 7.7% in Scenario A and to - 15.5% to 7.1% in Scenario B. Although the overall means of the formulas provide similar results, significant lesion-level differences are observed. The use of the worst view versus the average of two views provided similar results.


Assuntos
Angiografia Coronária/instrumentação , Estenose Coronária/diagnóstico por imagem , Vasos Coronários/diagnóstico por imagem , Modelos Cardiovasculares , Imagens de Fantasmas , Interpretação de Imagem Radiográfica Assistida por Computador/métodos , Idoso , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Valor Preditivo dos Testes , Reprodutibilidade dos Testes , Índice de Gravidade de Doença
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