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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Estudo de comportamento de fluxo através de modelo físico e computacional de aneurisma de aorta infra-renal obtido por tomografia. / Flow behavior study through physical and computacional model of infrarenal aortic aneurysm obtained by tomography.

Legendre, Daniel Formariz 06 February 2009 (has links)
Aneurisma de Aorta Abdominal (AAA) é definido como uma dilatação localizada e permanente da parede arterial, geralmente com ocorrência entre as artérias renais e as ilíacas, como conseqüência do enfraquecimento dessa parede ou devido a uma solicitação anormal sobre sua estrutura normal. Essa afecção acomete principalmente a população idosa acima de 65 anos de idade, tendo como principais fatores de risco: tabagismo, hipertensão arterial, histórico familiar e doença obstrutiva crônica pulmonar. A prevalência está aumentando nos últimos anos, havendo uma duplicação dos casos diagnosticados nos Estados Unidos (Bonamigo e Von Ristow, 1999). Hoje o AAA é a 13ª causa de morte nos Estados Unidos, em homens com mais de 65 anos e no caso de aneurisma roto, é a 3ª causa de morte súbita nos Estados Unidos. A mortalidade global do AAA roto está em torno de 80% nos países que têm verificação sistemática e compulsória da causa de óbitos. Isto ocorre devido ao fato de uma hemorragia substancial intra-abdominal geralmente ser acompanhada de atraso no transporte e diagnóstico, e da necessidade de cirurgia de emergência em pacientes idosos que, freqüentemente, tem uma significativa comorbidade renal e cardiopulmonar. Acredita-se que a formação e o crescimento do aneurisma de aorta abdominal são acompanhados do crescimento da tensão na parede da aorta e/ou de uma diminuição da capacidade do tecido de suportar tal tensão. A ruptura ocorre quando a tensão atuante na parede excede a tensão que pode ser suportada pelo tecido. O risco de ruptura aumenta com o crescimento do tamanho do aneurisma, da tensão na parede e é agravado quando associado à hipertensão arterial. No estudo foram obtidos dados morfológicos da região torácica de um paciente com a utilização de tomografia computadorizada multi-fatias. Essas imagens DICOM (Comunicação de Imagens Digitais em Medicina) foram tratadas para selecionar apenas a região de interesse, obtendo-se um modelo tridimensional da aorta infra-renal e artérias ilíacas. A partir daí, foi confeccionado um modelo físico com a utilização de prototipagem rápida. Um simulador cardiovascular controlado por computador foi desenvolvido com o intuito de replicar características fisiológicas e patológicas do sistema cardiovascular humano. Esse modelo de aneurisma foi utilizado para simulação em bancada experimental, onde é possível reproduzir alguns parâmetros como pressão, fluxo, temperatura, resistência e complacência vascular. Também foi gerado um modelo computacional onde os parâmetros obtidos na simulação in vitro foram utilizados como condição de contorno inicial para o estudo computacional. Foram adotados padrões normotenso e hipertenso, e os resultados computacionais e experimentais foram analisados e comparados. O trabalho propõe uma metodologia que possibilite a obtenção de dados anatômicos e hemodinâmicos relativos ao segmento arterial acometido pela afecção, com o objetivo de fornecer informações adicionais no diagnóstico do aneurisma de aorta. / Abdominal Aortic Aneurysm (AAA) is defined as a focal and permanent dilatation of the arterial wall, most often occurring in between the renal and iliac arteries, as consequence of arterial wall weakness or because of an abnormal solicitation of that normal structure. This disease primarily affects elderly population over 65 years of age, and the most important risk factors are smoking, hypertension, family history and chronic obstructive pulmonary disease. In the last years, the prevalence is rising up almost twice the diagnosed cases in the United States (Bonamigo and Von Ristow, 1999). Nowadays, AAA is the thirtieth cause of death in the United States, in the elderly masculine population over 65 years of age, and in case of ruptured aneurysm, it is the third cause of sudden death in the United States. The overall mortality rate is about 80% in countries with systematic and compulsory evaluation of death cause. This is due to the fact that substantial intra-abdominal hemorrhage is often accompanied by delays in transport and diagnoses, and the need for emergency surgery in elderly patients that frequently have significant renal and cardiopulmonary comorbidity. It is suggested that the formation and expansion of the AAA are accompanied by wall stress increasing and / or decreasing in the tissue capacity to withstand this stress. The rupture occurs when the wall stress exceed the stress the tissue can accept. The risk of rupture increases with aneurysm expansion, wall stress increasing and it is exacerbated when associated with arterial hypertension. In the present work, morphological data from thoracic region of the patient was acquired by using multi-slice CT (Computed Tomography). These DICOM images had been treated to select only the interest region, getting a three-dimensional infra-renal aortic and iliac model. Then, it was made a physical model by using rapid prototyping. This model was used for in vitro experimentation in a computer controlled mock system, in which it is possible to replicate physiological and pathological characteristics of human being cardiovascular system. Some parameters such as pressure, flow, temperature, vascular resistance and compliance can be reproduced by the use of a mock circulatory system. These parameters were used as initial boundary conditions in order to calibrate a computational model. It was adopted normotensive and hypertensive patterns and computational and experimental results were analyzed and compared. The paper proposes a methodology which allows the acquisition of anatomical and hemodynamic data on the vessel segment affected by the pathology, with the goal of providing additional information in the diagnosis of aortic aneurysm.
2

Estudo de comportamento de fluxo através de modelo físico e computacional de aneurisma de aorta infra-renal obtido por tomografia. / Flow behavior study through physical and computacional model of infrarenal aortic aneurysm obtained by tomography.

Daniel Formariz Legendre 06 February 2009 (has links)
Aneurisma de Aorta Abdominal (AAA) é definido como uma dilatação localizada e permanente da parede arterial, geralmente com ocorrência entre as artérias renais e as ilíacas, como conseqüência do enfraquecimento dessa parede ou devido a uma solicitação anormal sobre sua estrutura normal. Essa afecção acomete principalmente a população idosa acima de 65 anos de idade, tendo como principais fatores de risco: tabagismo, hipertensão arterial, histórico familiar e doença obstrutiva crônica pulmonar. A prevalência está aumentando nos últimos anos, havendo uma duplicação dos casos diagnosticados nos Estados Unidos (Bonamigo e Von Ristow, 1999). Hoje o AAA é a 13ª causa de morte nos Estados Unidos, em homens com mais de 65 anos e no caso de aneurisma roto, é a 3ª causa de morte súbita nos Estados Unidos. A mortalidade global do AAA roto está em torno de 80% nos países que têm verificação sistemática e compulsória da causa de óbitos. Isto ocorre devido ao fato de uma hemorragia substancial intra-abdominal geralmente ser acompanhada de atraso no transporte e diagnóstico, e da necessidade de cirurgia de emergência em pacientes idosos que, freqüentemente, tem uma significativa comorbidade renal e cardiopulmonar. Acredita-se que a formação e o crescimento do aneurisma de aorta abdominal são acompanhados do crescimento da tensão na parede da aorta e/ou de uma diminuição da capacidade do tecido de suportar tal tensão. A ruptura ocorre quando a tensão atuante na parede excede a tensão que pode ser suportada pelo tecido. O risco de ruptura aumenta com o crescimento do tamanho do aneurisma, da tensão na parede e é agravado quando associado à hipertensão arterial. No estudo foram obtidos dados morfológicos da região torácica de um paciente com a utilização de tomografia computadorizada multi-fatias. Essas imagens DICOM (Comunicação de Imagens Digitais em Medicina) foram tratadas para selecionar apenas a região de interesse, obtendo-se um modelo tridimensional da aorta infra-renal e artérias ilíacas. A partir daí, foi confeccionado um modelo físico com a utilização de prototipagem rápida. Um simulador cardiovascular controlado por computador foi desenvolvido com o intuito de replicar características fisiológicas e patológicas do sistema cardiovascular humano. Esse modelo de aneurisma foi utilizado para simulação em bancada experimental, onde é possível reproduzir alguns parâmetros como pressão, fluxo, temperatura, resistência e complacência vascular. Também foi gerado um modelo computacional onde os parâmetros obtidos na simulação in vitro foram utilizados como condição de contorno inicial para o estudo computacional. Foram adotados padrões normotenso e hipertenso, e os resultados computacionais e experimentais foram analisados e comparados. O trabalho propõe uma metodologia que possibilite a obtenção de dados anatômicos e hemodinâmicos relativos ao segmento arterial acometido pela afecção, com o objetivo de fornecer informações adicionais no diagnóstico do aneurisma de aorta. / Abdominal Aortic Aneurysm (AAA) is defined as a focal and permanent dilatation of the arterial wall, most often occurring in between the renal and iliac arteries, as consequence of arterial wall weakness or because of an abnormal solicitation of that normal structure. This disease primarily affects elderly population over 65 years of age, and the most important risk factors are smoking, hypertension, family history and chronic obstructive pulmonary disease. In the last years, the prevalence is rising up almost twice the diagnosed cases in the United States (Bonamigo and Von Ristow, 1999). Nowadays, AAA is the thirtieth cause of death in the United States, in the elderly masculine population over 65 years of age, and in case of ruptured aneurysm, it is the third cause of sudden death in the United States. The overall mortality rate is about 80% in countries with systematic and compulsory evaluation of death cause. This is due to the fact that substantial intra-abdominal hemorrhage is often accompanied by delays in transport and diagnoses, and the need for emergency surgery in elderly patients that frequently have significant renal and cardiopulmonary comorbidity. It is suggested that the formation and expansion of the AAA are accompanied by wall stress increasing and / or decreasing in the tissue capacity to withstand this stress. The rupture occurs when the wall stress exceed the stress the tissue can accept. The risk of rupture increases with aneurysm expansion, wall stress increasing and it is exacerbated when associated with arterial hypertension. In the present work, morphological data from thoracic region of the patient was acquired by using multi-slice CT (Computed Tomography). These DICOM images had been treated to select only the interest region, getting a three-dimensional infra-renal aortic and iliac model. Then, it was made a physical model by using rapid prototyping. This model was used for in vitro experimentation in a computer controlled mock system, in which it is possible to replicate physiological and pathological characteristics of human being cardiovascular system. Some parameters such as pressure, flow, temperature, vascular resistance and compliance can be reproduced by the use of a mock circulatory system. These parameters were used as initial boundary conditions in order to calibrate a computational model. It was adopted normotensive and hypertensive patterns and computational and experimental results were analyzed and compared. The paper proposes a methodology which allows the acquisition of anatomical and hemodynamic data on the vessel segment affected by the pathology, with the goal of providing additional information in the diagnosis of aortic aneurysm.
3

Infrared Neural Modulation: Photothermal Effects on Cortex Neurons Using Infrared Laser Heating

Xia, Qingling January 2018 (has links)
It would be of great value to have a precise and non-damaging neuromodulation technique in the field of basic neuroscience research and for clinical treatment of neurological diseases. Infrared neural modulation (INM) is a new modulation modality developed in the last decade, which uses pulsed or continues infrared (IR) light with a wavelength of 1200 to 2200 nm to directly alter neural signals. INM includes both infrared neural stimulation (INS) and infrared neural inhibition (INI). INM is widely investigated for use on peripheral nerves, cochlear nerve fibers, cardiac cells, and the central nervous system. This technique holds the advantages of contact-free and high spatiotemporal precision compared to the traditional electrical stimulation. It does not depend on genetic modification and exogenous absorbers as other optical techniques, such as the optogenetic technique and the enhanced near-infrared neural stimulation (e-NIR). These advantages make INM a viable technique for research and clinical applications. The primary mechanism of the INM is believed to be a photothermal effect, where the IR laser energy absorbed by water leads to a rapid local temperature change. However, so far the details of the mechanism of action potential (AP) generation and inhibition remain elusive. Another issueis that the cells may be endangeredbythe heat exposure, consequently triggering a physiologicalmalfunction or even permanent damage.These concernshave hindered the transfer of the INM technique to the clinical therapy.Therefore, the general aim of this study was to improve the understanding of the details of how INM affects the cells. Laser parameters for safe and efficient stimulation were investigated on the basis of being useful for clinical applications. A tailored heating model and in vitro INM experiments on cortex neurons were used to reach this goal.The first paper was a feasibility study. A 1550nm laser with a beam spot diameter of around 6 mm was used to irradiate the rat cortex neurons, which were seeded on multi-electrode arrays (MEA) and formed well-connected networks. A heating model based on an estimated laser beam (standard Gaussian distribution) was used to simulate temperaturechanges. The damage signal ratio (DSR),based on the temperature,was calculated to predict the heat damage. The average spike rate of all the working electrodes from two MEAs was used to evaluate the degree of theinhibition of the neural networks. Results IVshowed that it is possible to use the 1550 nm laser to safely inhibit the neural network activity and that the degree of the INI is dependent on the power of the laser.The second paper wasan application and mechanism study. The aim of this study was to investigate the safety, efficiency, and cellular mechanism of INI. The same laser as in paper Iwas used in this study. A 20 X objective was used to decrease the beam spot diameteraround 240 μm. The measured laser profile (high order Gaussian beam) was used in the heating model to predict the temperature. The model was verified by local temperature measurements viamicropipette. The action potential rates, measured by the MEA electrodes, were quantified for different temperatures. Bicuculline was added to the cortex neuron cultures to induce hyperexcitation of the neural network. The results showed that the INI is temperature dependent and that the temperature needs to be less than 46 °C at 30 s laser irradiation for safe inhibition. The IR laser couldalso be used to inhibit the hyperexcitedactivity. The degree of inhibition, for the assessed subpopulation of neurons, was better correlated with the action potential amplitude than the width of it and INIcan be accomplished without inhibitory synapses / <p>QC 20180920</p><p></p>

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