Navegando por Assunto "Biomedical engineering"

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Acesso aberto (Open Access)
Desenvolvimento de métodos de processamento e inteligência computacional no ECG ambulatorial
(Universidade Federal do Pará, 2012-04-26) EVANGELISTA NETO, João; VÁZQUEZ SEISDEDOS, Carlos Román; http://lattes.cnpq.br/5337885650253619; OLIVEIRA, Roberto Célio Limão de; http://lattes.cnpq.br/4497607460894318
Ambulatory monitoring of the electrocardiogram (ECG) allows to follow the patient's daily activities during periods of 24 hours (or more) making possible the study of cases with potentially fatal arrhythmic episodes. However, the major technological challenge that this type of monitoring faces is the loss of information due to the presence movement-related noise and artefacts. The analysis of the QT interval of the surface electrocardiogram or ventricular depolarization and repolarization interval is a non-invasive technique with a high value for the diagnosis and prognostics of cardiopathies and neuropathies, as well as for the prediction of sudden cardiac death. The analysis of the QT-interval standard deviation provides information about the dispersion (time or spatial) of ventricular repolarization. Hovever the presence of noise leads to errors in the detection of the T-wave end, which are non negligible due to small values of QT standard deviation in both pathological and healthy subjects. The main aim of this PhD thesis is to improve ambulatory ECG processing methods using computational intelligence, and specifically those involved in the detection of the T wave end and morphologic recognition of heartbeats, which could invalidate the QT interval variability analysis. A new approach and algorithm was proposed to identify the T-wave end, based on the computation of Trapezium’s areas. The method was validated (in terms of accuracy and repeatability), using signals from the Physionet QT Database. The performance of the proposed method in noisy conditions has been tested and compared with one of the most used approaches for estimating the T-wave end point, based on the threshold on the first derivative. The suggested computational intelligence method combines the features extraction using non-linear principal components analysis method and the multilayer perceptron neural network. The trapezium-based approach showed a good performance in noisy conditions and does not rely on any empirical threshold. It is adequate for use in scenarios where the levels of broadband noise are significant. The beats morphologic recognition methods were evaluated using ambulatory signals with and without artefacts from international prestigious databases, showing a good performance.
Acesso aberto (Open Access)
Estudo e desenvolvimento de um protótipo para redução da interferência de modo comum usando balanceamento dinâmico de impedância aplicado em biosensores e sensores eletroresistivos
(Universidade Federal do Pará, 2013-10-25) NEGRÃO, João Francisco Ribeiro; ARAÚJO, Guilherme Augusto Limeira; http://lattes.cnpq.br/8261564685433904; COSTA JÚNIOR, Carlos Tavares da; http://lattes.cnpq.br/6328549183075122
Electromagnetic interference caused by the electric power line adversely affects the signals of electronic instruments, especially those with low amplitude levels. This type of interference is known as common-mode interference. There are many methods and architectures used to minimize the influence of this kind of interference on electronic instruments, the most common of which is the use of band-reject filters. This paper presents the analysis, development, prototype and test of a new reconfigurable filter architecture for biomedical instruments and measuring data of high complexity fluid flow, such as two phase flows, interference in the measurement circuit may affect the measured data, aiming to reduce the common-mode interference and preserve the useful signal components in the same frequency range as that of the noise, using the technique of dynamic impedance balancing. . Also, any measurement system also suffers interference in the power line frequency (50/60 Hz in Brazil and France, 60Hz in United States of America). The circuit blocks were mathematically modeled and the overall closed-loop transfer function was derived. Then the project was described and simulated in the VHDL_AMS language and also in an electronics simulation software, using discrete component blocks, with and without feedback. After theoretical analysis and simulation results, a prototype circuit was built and tested using as input a signal obtained from ECG electrodes and Resistivity Needle Probes. The results from the experimental circuit matched those from simulation: a 97.6% noise reduction was obtained in simulations using a sinusoidal signal, and an 86.66% reduction was achieved using ECG electrodes in experimental tests. In both cases, the useful signal was preserved. The method and its architecture can be applied to attenuate interferences, which occur in the same frequency band as that of the useful signal components, while preserving these signals.