Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 5.689
Filtrar
1.
Expert Rev Med Devices ; 18(4): 395-405, 2021 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-33710950

RESUMO

Introduction: Electromagnetic interference (EMI) of cardiovascular implantable electronic devices (CIED) can lead to malfunctions and pose a danger for implant carriers. The increased use of DC technologies, e.g. in electric mobility, creates more static fields representing an increasing hazard for implant carriers.Areas covered: A combination of approaches was used to determine thresholds for EMI by static fields. A literature search was conducted to identify relevant EMI mechanisms and to extract possible thresholds. The literature search revealed four interference mechanisms caused by static magnetic fields and none for static electric fields. Due to the scarce information on motion-induced EMI, numerical simulations were performed to obtain a threshold. The simulation results were evaluated using medical product standards and benchmark tests on commercially available CIEDs. The results show that motion-induced interference should not occur below the activation of the magnetic safety switch (reed switch or Hall-effect sensor, MSS).Expert opinion: The determined threshold for motion-induced EMI at 24.8 mT shows that the MSS activation is still the most relevant mechanism that can occur at 0.8 mT. Limit values for the general population do not protect implant carriers from EMI.


Assuntos
Desfibriladores Implantáveis , Campos Eletromagnéticos , Campos Magnéticos , Simulação por Computador , Humanos , Movimento (Física) , Análise Numérica Assistida por Computador
2.
Toxicol Appl Pharmacol ; 414: 115424, 2021 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-33524444

RESUMO

For the determination of acute toxicity of chemicals in zebrafish (Danio rerio) embryos, the OECD test guideline 236, relative to the Fish Embryo Toxicity Test (FET), stipulates a dose-response analysis of four lethal core endpoints and a quantitative characterization of abnormalities including their time-dependency. Routinely, the data are analyzed at the different observation times separately. However, observations at a given time strongly depend on the previous effects and should be analyzed jointly with them. To solve this problem, we developed multistate models for occurrence of developmental malformations and live events in zebrafish embryos exposed to eight concentrations of valproic acid (VPA) the first five days of life. Observations were recorded daily per embryo. We statistically infer on model structure and parameters using a numerical Bayesian framework. Hatching probability rate changed with time and we compared five forms of its time-dependence; a constant rate, a piecewise constant rate with a fixed hatching time at 48 h post fertilization, a piecewise constant rate with a variable hatching time, as well as a Hill and Gaussian form. A piecewise constant function of time adequately described the hatching data. The other transition rates were conditioned on the embryo body concentration of VPA, obtained using a physiologically-based pharmacokinetic model. VPA impacted mostly the malformation probability rate in hatched and non-hatched embryos. Malformation reversion probability rates were lowered by VPA. Direct mortality was low at the concentrations tested, but increased linearly with internal concentration. The model makes full use of data and gives a finer grain analysis of the teratogenic effects of VPA in zebrafish than the OECD-prescribed approach. We discuss the use of the model for obtaining toxicological reference values suitable for inter-species extrapolation. A general result is that complex multistate models can be efficiently evaluated numerically.


Assuntos
Anormalidades Induzidas por Medicamentos/etiologia , Modelos Biológicos , Teratógenos/toxicidade , Testes de Toxicidade Aguda , Ácido Valproico/toxicidade , Anormalidades Induzidas por Medicamentos/embriologia , Animais , Teorema de Bayes , Simulação por Computador , Relação Dose-Resposta a Droga , Embrião não Mamífero/anormalidades , Embrião não Mamífero/efeitos dos fármacos , Análise Numérica Assistida por Computador , Teratógenos/farmacocinética , Toxicocinética , Ácido Valproico/farmacocinética , Peixe-Zebra/embriologia
3.
Am J Physiol Heart Circ Physiol ; 320(4): H1601-H1608, 2021 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-33606582

RESUMO

Central systolic blood pressure (cSBP, the peak of the central waveform) is usually regarded as the determinant of peripheral systolic blood pressure with amplification of peripheral systolic blood pressure (pSBP) measured with reference to cSBP. However, the earlier portion of the central waveform up to the first systolic shoulder (P1) may be the major determinant of pSBP. We performed in silico simulation studies and examined previously acquired experimental data (n = 131) in which peripheral and central blood pressure waveforms had been acquired both invasively and noninvasively to examine the determinants of pSBP. Measurements were made at baseline and during perturbation of hemodynamics by inotropic and vasoactive drugs. In silico simulations using a central-to-peripheral transfer function demonstrated that pSBP is dependent on P1 and the rate of change (dP/dt) of central pressure up to the time of P1 but not cSBP. In computational simulations, peripheral reflection in the radial artery was closely related to dP/dt, and 97% of the variability in amplification as measured with reference to P1 was explained by dP/dt. In vivo, amplification of pSBP over P1 was correlated with dP/dt (R > 0.75, P < 0.0001 for all data sets), and P1 and dP/dt were independently correlated with pSBP, explaining 90% of the variability in pSBP. We conclude that P1 and dP/dt are major determinants of pSBP and that pSBP and cSBP are, in part, determined by different cardiac, central, and peripheral vascular properties.NEW & NOTEWORTHY Peripheral systolic BP is determined mainly by the first shoulder and the rate of rise of the central systolic blood pressure waveform rather than the peak of this waveform (central systolic BP). Peripheral and central systolic blood pressure are determined by different cardiac and vascular properties.


Assuntos
Pressão Arterial , Artérias/fisiopatologia , Determinação da Pressão Arterial , Hipertensão/diagnóstico , Modelos Cardiovasculares , Função Ventricular Esquerda , Adulto , Idoso , Estudos de Casos e Controles , Simulação por Computador , Feminino , Humanos , Hipertensão/fisiopatologia , Masculino , Pessoa de Meia-Idade , Análise Numérica Assistida por Computador , Valor Preditivo dos Testes , Sístole , Fatores de Tempo
4.
Microvasc Res ; 133: 104102, 2021 01.
Artigo em Inglês | MEDLINE | ID: mdl-33166578

RESUMO

This study describes a computational algorithm to determine vascular permeability constants from time-lapse imaging data without concurrent knowledge of the arterial input function. The algorithm is based on "blind" deconvolution of imaging data, which were generated with analytical and finite-element models of bidirectional solute transport between a capillary and its surrounding tissue. Compared to the commonly used Patlak analysis, the blind algorithm is substantially more accurate in the presence of solute delay and dispersion. We also compared the performance of the blind algorithm with that of a simpler one that assumed unidirectional transport from capillary to tissue [as described in Truslow et al., Microvasc. Res. 90, 117-120 (2013)]. The algorithm based on bidirectional transport was more accurate than the one based on unidirectional transport for more permeable vessels and smaller extravascular distribution volumes, and less accurate for less permeable vessels and larger extravascular distribution volumes. Our results indicate that blind deconvolution is superior to Patlak analysis for permeability mapping under clinically relevant conditions, and can thus potentially improve the detection of tissue regions with a compromised vascular barrier.


Assuntos
Algoritmos , Permeabilidade Capilar , Processamento de Imagem Assistida por Computador , Microcirculação , Modelos Cardiovasculares , Imagem com Lapso de Tempo , Animais , Velocidade do Fluxo Sanguíneo , Análise de Elementos Finitos , Humanos , Análise Numérica Assistida por Computador , Fatores de Tempo
5.
PLoS One ; 15(12): e0243832, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-33318708

RESUMO

Precise and reasonable evaluation of the multi-attribute value of medical system is the basis for hospitals to implement total quality management. Excellent medical system is necessary as a part of modern urban governance. However, most of medical value evaluation work relies on scale and artificial scoring at present, lacking in objectivity. Therefore, a scientific and comprehensive medical value evaluation system is needed urgently to give full play to the guiding role of value evaluation and promote the improvement of the medical service system. In this study, DEMATEL and information entropy are used to quantify the degree of mutual influence between system indicators and the differences in medical market performance respectively, so as to obtain the objective index weight. Hypertension has the highest incidence in the whole chronic disease system, which seriously affects people's daily life. Based on the existing hypertension diagnosis and treatment index system, a comprehensive and objective evaluation model is established to evaluate the hypertension diagnosis and treatment behaviors of different medical institutions, which achieves good result. This method has effectively improved the relative deficiency of one-sided subjective evaluation and has a great guiding significance for the comparison of treatment in departments and the economical use of medical resources.


Assuntos
Tomada de Decisão Clínica , Entropia , Serviços de Saúde , Hipertensão/diagnóstico , Idoso , China , Hospitais , Humanos , Análise Numérica Assistida por Computador , Padrões de Referência
6.
PLoS One ; 15(8): e0237862, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32853210

RESUMO

As passive investment through index funds and Exchange Traded Funds (ETFs) has become pervasive, the structure of corporate control in the global capital market is more complex than before. We propose a new model and calculation algorithm to measure a shareholder's power to control corporations in the global economy. Our method takes into account how fragmented voting rights attached to dispersed ownership may be consolidated to generate corporate control. Analyzing the ownership holdings in 49 million companies worldwide by 69 million shareholders in 2016, we find that the landscape of global corporate control appears differently if we adequately evaluate indirect influence via dispersed ownership. In particular, a larger portion of corporate control appears to be concentrated in the hands of sovereign governments than has been recognized before. Yet, such governmental capacities are "hidden" if we use the conventional method. Moreover, financial institutions appear to not be as powerful as emphasized before. These results point to important financial and political risks both for scholars and policymakers.


Assuntos
Organizações/economia , Propriedade/economia , Algoritmos , Análise Numérica Assistida por Computador
7.
PLoS Biol ; 18(7): e3000462, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32697779

RESUMO

Most fish swim with body undulations that result from fluid-structure interactions between the fish's internal tissues and the surrounding water. Gaining insight into these complex fluid-structure interactions is essential to understand how fish swim. To this end, we developed a dedicated experimental-numerical inverse dynamics approach to calculate the lateral bending moment distributions for a large-amplitude undulatory swimmer that moves freely in three-dimensional space. We combined automated motion tracking from multiple synchronised high-speed video sequences, computation of fluid dynamic stresses on the swimmer's body from computational fluid dynamics, and bending moment calculations using these stresses as input for a novel beam model of the body. The bending moment, which represent the system's net actuation, varies over time and along the fish's central axis due to muscle actions, passive tissues, inertia, and fluid dynamics. Our three-dimensional analysis of 113 swimming events of zebrafish larvae ranging in age from 3 to 12 days after fertilisation shows that these bending moment patterns are not only relatively simple but also strikingly similar throughout early development and from fast starts to periodic swimming. This suggests that fish larvae may produce and adjust swimming movements relatively simply, yet effectively, while restructuring their neuromuscular control system throughout their rapid development.


Assuntos
Análise Numérica Assistida por Computador , Natação/fisiologia , Peixe-Zebra/fisiologia , Animais , Fenômenos Biomecânicos , Fertilização , Larva/fisiologia , Modelos Biológicos , Movimento (Física) , Cauda
8.
Comput Methods Biomech Biomed Engin ; 23(13): 987-1004, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32594768

RESUMO

An image-based numerical algorithm is presented for simulating blood flow through the liver tissue. First, a geometric model is constructed by applying image processing techniques on a real microscopic image of a liver tissue. Then, incompressible blood flow through liver lobules is simulated. Effects of tissue heterogeneity and deformity, presence/absence of the second central vein in a particular lobule, and apparent sinusoids density in the liver cross section on the blood flow are investigated. Numerical results indicate that the existence of thick low permeability vascular septum, high permeability sinusoids, and lobule tissue heterogeneity can considerably affect interlobular and intralobular blood flow.


Assuntos
Processamento de Imagem Assistida por Computador , Circulação Hepática/fisiologia , Fígado/irrigação sanguínea , Fígado/diagnóstico por imagem , Modelos Anatômicos , Análise Numérica Assistida por Computador , Perfusão , Animais , Velocidade do Fluxo Sanguíneo , Pressão Sanguínea , Simulação por Computador , Hemorreologia , Permeabilidade , Reprodutibilidade dos Testes , Suínos
9.
Comput Methods Biomech Biomed Engin ; 23(13): 968-980, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32530754

RESUMO

A solid multi-layered concentric sphere with Gaussian space source is considered as the tissue model for magnetic hyperthermia treatment. The generalized dual-phase-lag model of bioheat transfer is used to describe the behavior of heat transport in tissue in the hyperthermia treatment process for accounting the local non-equilibrium effect. The effects of blood perfusion with the transient temperature are included in the tissue model. The hybrid numerical scheme based on Laplace transform, change of variables, and the modified discretization technique is extended to solve the present problem. The analytical solution for constant heat generation in the inner sphere is presented and evidences the accuracy and rationality of the present numerical results. In an ideal hyperthermia treatment, all the diseased tissues should be selectively heated without affecting any healthy tissue. Attempting to achieve the ideal temperature distribution, the thermal dose is estimated at the specified condition. The corresponding thermal efficacy of tumor damage has also been assessed based on the Arrenius equation.


Assuntos
Temperatura Alta , Hipertermia Induzida , Fenômenos Magnéticos , Análise Numérica Assistida por Computador , Humanos , Modelos Biológicos , Neoplasias/terapia , Distribuição Normal , Reprodutibilidade dos Testes
10.
Comput Methods Biomech Biomed Engin ; 23(12): 894-905, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32519914

RESUMO

Stenosis in the bifurcated coronary artery has attracted wide attention among the researchers. Many investigations have been carried out by means of Computational Fluid Dynamics (CFD) to better understand the physical mechanism inside the stenotic bifurcated artery. However, the main focus of the existing publications is limited to the variation of hemodynamic parameters affected by the stenosis and bifurcation structure. The present study aims to make further evaluations of stenosis development and diagnostic lesion assessments based on the critical values of hemodynamic and practical diagnostic parameters. The bifurcated coronary artery with initial stenosis source has been studied in 2 D unsteady model. Different locations of initial stenosis source have been found to greatly affect the orientation of the further stenosis development. In addition, different stenosis severities (diameter stenosis: 30%, 50% and 70%), different stenosis lengths (3 mm, 6 mm and 9 mm) and different pulse rates (75 bpm, 100 bpm and 120 bpm) as controlling parameters have been investigated.


Assuntos
Estenose Coronária/diagnóstico , Estenose Coronária/fisiopatologia , Vasos Coronários/fisiopatologia , Análise Numérica Assistida por Computador , Velocidade do Fluxo Sanguíneo , Simulação por Computador , Hemodinâmica , Humanos , Hidrodinâmica , Modelos Cardiovasculares , Estresse Mecânico
11.
Comput Methods Biomech Biomed Engin ; 23(12): 854-867, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32479190

RESUMO

Design optimization for cementless hip prosthesis signifies one of the key topics of research to improve its performances. However, majority of the studies have not considered the presence of uncertainties while it has been shown that a deterministic optimization leads to an unreliable design. In this paper, a multi-objective reliability-based design optimization (MORBDO) procedure is proposed for cementless hip prosthesis design. The proposed methodology consists in combining the finite element simulation (FES), surrogating techniques and optimization procedure. The constructed meta-models are validated and compared using different measures such as error predictions and cross-validation (CV). The results show that the constrained non-dominated sorting genetic algorithm (C-NSGA-II) coupled with the hybrid method (HM) was capable to generate well-distributed reliable Pareto solutions.


Assuntos
Algoritmos , Cimentos Ósseos/farmacologia , Prótese de Quadril , Simulação por Computador , Humanos , Análise Numérica Assistida por Computador , Reprodutibilidade dos Testes , Estresse Mecânico
12.
Microvasc Res ; 131: 104010, 2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-32335268

RESUMO

Glutathione (GSH) and GSH/glutathione peroxidase (GPX) enzyme system is essential for normal intracellular homeostasis and gets disturbed under pathophysiologic conditions including endothelial dysfunction. Overproduction of reactive oxidative species (ROS) and reactive nitrogen species (RNS) including superoxide (O2•-), and the loss of nitric oxide (NO) bioavailability is a characteristic of endothelial dysfunction. The GSH/GPX system play an important role in eliminating ROS/RNS. Studies have provided important information regarding the interactions of ROS/RNS with the GSH/GPX in biological systems; however, it is not clear how this cross talk affect these reactive species and GSH/GPX enzyme system, under physiologic and oxidative/nitrosative stress conditions. In the present study, we developed a detailed endothelial cell kinetic model to understand the relationship amongst the key enzyme systems including GSH, GPX, peroxiredoxin (Prx) and reactive species, such as hydrogen peroxide (H2O2), peroxynitrite (ONOO-), and dinitrogen trioxide (N2O3). Our simulation results showed that the alterations in the generation rates of O2•- and NO led to the formation of a wide range of ROS and RNS. Simulations performed by varying the ratio of O2•- to NO generation rates as well as GSH and GPX concentrations showed that the GPX reducing capacity was dependent on GSH availability, level of oxidative/nitrosative stress, and can be attributed to N2O3 levels, but not to H2O2 and ONOO-. Our results showed that N2O3 mediated switch-like depletion in GSH and the incorporation of Prx had no considerable effect on the ROS/RNS species other than ONOO- and H2O2. The analysis presented in this study will improve our understanding of vascular diseases in which the levels and oxidation states of GSH, GPX and/or Prx are significantly altered and pharmacological interventions show limited benefits.


Assuntos
Células Endoteliais/enzimologia , Glutationa Peroxidase/metabolismo , Glutationa/metabolismo , Modelos Cardiovasculares , Espécies Reativas de Nitrogênio/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Animais , Simulação por Computador , Humanos , Cinética , Estresse Nitrosativo , Análise Numérica Assistida por Computador , Oxirredução , Estresse Oxidativo , Transdução de Sinais
13.
Microvasc Res ; 130: 104007, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32305349

RESUMO

Magnetic nanoparticle targeting in tumor areas is examined by an integrated consideration of the transport steps from the microcirculation to the vascular walls, through their pores and into the interstitium. Brownian, flow- and magnetically induced forces and fluxes are compared on the basis of order-of-magnitude estimates and numerical simulations. The main resistance to nanoparticle transport is found to be within the interstitium, since fluxes there are much smaller than the extravasation fluxes, and the latter are much smaller than the convective-diffusive ones within the microvasculature. For typical nanoparticle sizes, magnetic properties and strengths of magnetic fields as in MRI equipment, magnetic targeting is rather unlikely to play a significant role in directing nanoparticles towards vascular walls or through vascular pores. However, magnetic drift can have an effect within the interstitium and a tangible overall outcome, despite the fact that typical magnetic forces are smaller than Brownian ones or interstitial flow convective forces. The reason behind such an effect has to do with the much larger length scales involved in interstitial transport. Magnetic drift creates a front of large nanoparticle concentrations, flooding the inadequately perfused and poorly accessible tumor area. On the basis of time-scale estimates, it is suggested that sequential cycles of magnetic nanoparticle dosage may help in more efficient access of cell layers ever closer to the tumor center. The present results may assist in the quest for optimal parameters and conditions, given the conflicting requirements for particles small enough to evade hydrodynamic and steric hindrances in vascular pores and the interstitium, yet large enough to bear a substantial magnetic load.


Assuntos
Antineoplásicos/metabolismo , Portadores de Fármacos , Magnetismo , Nanopartículas de Magnetita/química , Microvasos/metabolismo , Modelos Biológicos , Nanomedicina , Neoplasias/irrigação sanguínea , Neoplasias/metabolismo , Animais , Antineoplásicos/administração & dosagem , Antineoplásicos/química , Transporte Biológico , Permeabilidade Capilar , Difusão , Composição de Medicamentos , Humanos , Hidrodinâmica , Neoplasias/tratamento farmacológico , Análise Numérica Assistida por Computador
14.
Sci Rep ; 10(1): 6537, 2020 04 16.
Artigo em Inglês | MEDLINE | ID: mdl-32300180

RESUMO

Ultrasounds (US) has been used in the past decades as a non-invasive imaging modality. Although employed extensively in clinical applications for soft tissue imaging, the acoustic beams can also be used for sensing and actuation for biological implants. In this paper we present a unified three dimensional (3D) computational framework to simulate the performance and response of deeply implanted devices to US stimulation and composed by a double piezoelectric layer with different material composition and configurations. The model combines the temporally-invariant distribution of the scattered pressure field arising from the presence of scatterers and attenuators in the domain of simulation, with the time-delay propagation of waves caused by refraction, to solve the Forward Problem in US within the breast and lower abdominal regions. It was found that a lens-shaped implant produces higher peak echoes in the breast for frequencies ≤ 6 MHz whereas, in the liver, similar strengths are obtained for the lens and disk-shaped implants in the higher spectrum. Regarding material composition, a combination of LiNbO3 with PZT-5A yielded higher amplitude signals, when the double layer thickness is comparable to the wavelength of excitation. Experimental validation of the proposed model was carried out in the presence of a synthetic anatomical phantom of the breast and water tank to investigate the acoustic signals generated by disk-shaped implants when stimulated by external US sources in the harmonic and impulsive regimes of wave propagation. The implantation of a double piezoelectric layer inside the human body can, in the future, provide a high resolution system for the detection of surgical site infection as well as tumour growth and other systemic inflammatory responses originating deeply in soft tissues.


Assuntos
Simulação por Computador , Próteses e Implantes , Desenho de Prótese , Ultrassonografia , Acústica , Mama/diagnóstico por imagem , Eletricidade , Feminino , Humanos , Imageamento Tridimensional , Análise Numérica Assistida por Computador , Imagens de Fantasmas , Reprodutibilidade dos Testes , Processamento de Sinais Assistido por Computador , Transdutores
15.
Cardiovasc Eng Technol ; 11(3): 254-267, 2020 06.
Artigo em Inglês | MEDLINE | ID: mdl-32297154

RESUMO

PURPOSE: Modeling of hemolysis due to fluid stresses faces significant methodological challenges, particularly in geometries with turbulence or complex flow patterns. It is currently unclear how existing phenomenological blood-damage models based on laminar viscous stresses can be implemented into turbulent computational fluid dynamics simulations. The aim of this work is to generalize the existing laminar models to turbulent flows based on first principles, and validate this generalization with existing experimental data. METHODS: A novel analytical and numerical framework for the simulation of flow-induced hemolysis based on the intermittency-corrected turbulent viscous shear stress (ICTVSS) is introduced. The proposed large-eddy simulation framework is able to seamlessly transition from laminar to turbulent conditions in a single flow domain by linking laminar shear stresses to dissipation of mechanical energy, accounting for intermittency in turbulent dissipation, and relying on existing power-law hemolysis models. Simulations are run to reproduce previously published hemolysis data with bovine blood in a benchmark geometry. Two sets of experimental data are relied upon to tune power-law parameters and justify that tuning. The first presents hemolysis measurements in a simple laminar flow, and the second is hemolysis in turbulent flow through the FDA benchmark nozzle. Validation is performed by simulation of blood injected into a turbulent jet of phosphate-buffered saline, with modifications made to account for the local concentration of blood. RESULTS: Hemolysis predictions are found to be very sensitive to power-law parameters in the turbulent case, though a set of parameters is presented that both matches the turbulent data and is well-justified by the laminar data. The model is shown to be able to predict the general behavior of hemolysis in a second turbulent case. Results suggest that wall shear may play a dominant role in most cases. CONCLUSION: The ICTVSS framework of generalizing laminar power-law models to turbulent flows shows promise, but would benefit from further numerical validation and carefully designed experiments.


Assuntos
Simulação por Computador , Aprovação de Equipamentos , Coração Auxiliar/efeitos adversos , Hemodinâmica , Hemólise , Modelos Teóricos , United States Food and Drug Administration , Velocidade do Fluxo Sanguíneo , Viscosidade Sanguínea , Teste de Materiais , Análise Numérica Assistida por Computador , Desenho de Prótese , Reprodutibilidade dos Testes , Medição de Risco , Fatores de Risco , Estresse Mecânico , Estados Unidos
16.
Artigo em Chinês | MEDLINE | ID: mdl-32268688

RESUMO

Objective: To investigate the effect of nasal septum perforation (SP) with different locations and sizes on nasal airflow by means of numerical simulation. Methods: Two healthy persons with normal nasal anatomy were enrolled in this study, including a 45 years old male (case 1) and a 36 years old female (case 2). Nasal CT data was used as the basis to create nasal airway numerical models of nasal SP with different locations (anterior caudal, central caudal, posterior caudal and anterior cranial) and sizes (diameter of 10 mm and 5 mm respectively). The inspiratory airflow characteristics (nasal cavity volume, nasal cavity wall area, pressure, nasal resistance, temperature, airflow velocity, wall shear stress, airflow-rate partitioning and vortex) of these nasal airway numerical models were simulated and analyzed. Pearson correlation analysis was performed between nasal resistances, airflow temperature and nasal cavity wall area. Results: In terms of pressure and nose resistance, the anterior caudal and larger size SP lead to more obvious variation of pressure distribution, and increased nasal resistance was especially found in the nasal cavity with anterior and medium caudal SP. In terms of temperature, the anterior (caudal and cranial) and larger size SP had significant effect on local temperature gradient as same as the anterior cranial and smaller size SP. Nasal heating efficiency was lower in nasal model with the anterior and larger size SP than that in the normal model. The temperature difference from the nostril to the end of nasal septum had positive correlation with nasal cavity wall area (R(2) value of case 1 and case 2 was 0.69, 0.41, respectively, all P<0.01). In terms of airflow velocity, the anterior caudal and cranial SP had more significant effect on the average airflow velocity in the nasal cavity. The anterior and medium caudal SP could make the airflow distribution in the asymmetric bilateral nasal cavity more unbalanced compared to the bilateral symmetrical nasal models. The anterior and medium SP resulted in a more pronounced vortex distribution than the posterior SP. Conclusions: The effect of SP on nasal cavity is related to its location and size. The anterior and larger size SP shows more negative influence on intranasal pressure, nasal resistance, heat transmission efficiency, airflow-rate partitioning than the posterior and smaller size SP.


Assuntos
Simulação por Computador , Modelos Biológicos , Cavidade Nasal , Perfuração do Septo Nasal/patologia , Adulto , Feminino , Humanos , Inalação , Masculino , Pessoa de Meia-Idade , Septo Nasal , Análise Numérica Assistida por Computador , Temperatura
17.
Comput Methods Biomech Biomed Engin ; 23(8): 432-444, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32126825

RESUMO

Modeling the evolution of bone density is relevant for understanding, simulation and possible prediction of bone response to external and internal influences. In this work we present a formulation for the bone density evolution process that takes into account not only the commonly considered mechanical stimulus, but, as novelty, also the influence of the availability of nutrients and hormones, with its implementation pursued within the finite element method. A simple uni-axial extension test is used to illustrate and compare our novel model against the classical approach. The results of the proposed modified model are promising for application to real-life problems.


Assuntos
Remodelação Óssea/fisiologia , Disponibilidade Biológica , Fenômenos Biomecânicos , Densidade Óssea/fisiologia , Simulação por Computador , Fêmur/fisiologia , Análise de Elementos Finitos , Humanos , Úmero/fisiologia , Modelos Biológicos , Análise Numérica Assistida por Computador , Estresse Mecânico , Suporte de Carga
18.
Chaos ; 30(2): 023131, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-32113239

RESUMO

The interaction among spreading processes on a complex network is a nontrivial phenomenon of great importance. It has recently been realized that cooperative effects among infective diseases can give rise to qualitative changes in the phenomenology of epidemic spreading, leading, for instance, to abrupt transitions and hysteresis. Here, we consider a simple model for two interacting pathogens on a network and we study it by using the message-passing approach. In this way, we are able to provide detailed predictions for the behavior of the model in the whole phase-diagram for any given network structure. Numerical simulations on synthetic networks (both homogeneous and heterogeneous) confirm the great accuracy of the theoretical results. We finally consider the issue of identifying the nodes where it is better to seed the infection in order to maximize the probability of observing an extensive outbreak. The message-passing approach provides an accurate solution also for this problem.


Assuntos
Epidemias , Modelos Biológicos , Coinfecção/epidemiologia , Simulação por Computador , Surtos de Doenças , Humanos , Análise Numérica Assistida por Computador , Probabilidade
19.
Comput Methods Biomech Biomed Engin ; 23(9): 467-475, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32159397

RESUMO

The purpose of this study is to investigate the hemodynamic significance of various degrees of coronary area of stenosis (AS) and multiple sequential stenoses (MSS) in normal and hypertension pressure conditions. MSS in a single branch coronary artery pose challenges to determine the physiological assessment in the prevalent invasive intervention. The hemodynamic parameters of each stenosis are influenced by other stenoses in the single branch of MSS coronary artery. In this study, we entirely use open source tools and techniques for coronary computed tomography angiography (CCTA) image segmentation, 3D reconstruction, grid generation and hemodynamic simulations. The results yield different hemodynamic parameters such as velocity magnitude, mean arterial pressure difference, flow-pressure linear relation, wall shear stress (WSS) and eventually virtual fractional flow reserve (vFFR) allowing for the prediction and the assessment of lumen area severity conditions in MSS coronaries.


Assuntos
Estenose Coronária/fisiopatologia , Vasos Coronários/fisiopatologia , Hemodinâmica , Hipertensão/fisiopatologia , Modelos Cardiovasculares , Idoso , Simulação por Computador , Constrição Patológica , Estenose Coronária/diagnóstico por imagem , Vasos Coronários/diagnóstico por imagem , Humanos , Masculino , Análise Numérica Assistida por Computador
20.
PLoS One ; 15(3): e0229738, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32160222

RESUMO

Ultrasound has many uses, such as in medical imaging, monitoring of crystallization, characterization of emulsions and suspensions, and disruption of cell membranes in the food industry. It can also affect microbial cells by promoting or slowing their growth and increasing the production of some metabolites. However, the exact mechanism explaining the effect of ultrasound has not been identified yet. Most equipment employed to study the effect of ultrasound on microorganisms has been designed for other applications and then only slightly modified. This results in limited control over ultrasound frequency and input power, or pressure distribution in the reactor. The present study aimed to obtain a well-defined reactor by simulating the pressure distribution of a sonobioreactor. Specifically, we optimized a sonotrode to match the bottle frequency and compared it to measured results to verify the accuracy of the simulation. The measured pressure distribution spectrum presented the same overall trend as the simulated spectrum. However, the peaks were much less intense, likely due to non-linear events such as the collapse of cavitation bubbles. To test the application of the sonobioreactor in biological systems, two biotechnologically interesting microorganisms were assessed: an electroactive bacterium, Geobacter sulfurreducens, and a lignocellulose-degrading fungus, Fusarium oxysporum. Sonication resulted in increased malate production by G. sulfurreducens, but no major effect on growth. In comparison, morphology and growth of F. oxysporum were more sensitive to ultrasound intensity. Despite considerable morphological changes at 4 W input power, the growth rate was not adversely affected; however, at 12 W, growth was nearly halted. The above findings indicate that the novel sonobioreactor provides an effective tool for studying the impact of ultrasound on microorganisms.


Assuntos
Reatores Biológicos/microbiologia , Fusarium/crescimento & desenvolvimento , Geobacter/crescimento & desenvolvimento , Análise Numérica Assistida por Computador , Sonicação , Calorimetria , Simulação por Computador , Fusarium/ultraestrutura , Geobacter/metabolismo , Malatos/metabolismo , Metaboloma , Pressão , Vibração
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...