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Three-dimensional electrical impedance, tomography: A topology optimization approach

MELLO, Luis Augusto Motta; LIMA, Cicero Ribeiro De; AMATO, Marcelo Britto Passos; LIMA, Raul Gonzalez; SILVA, Emilio Carlos Nelli
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.45%
Electrical impedance tomography is a technique to estimate the impedance distribution within a domain, based on measurements on its boundary. In other words, given the mathematical model of the domain, its geometry and boundary conditions, a nonlinear inverse problem of estimating the electric impedance distribution can be solved. Several impedance estimation algorithms have been proposed to solve this problem. In this paper, we present a three-dimensional algorithm, based on the topology optimization method, as an alternative. A sequence of linear programming problems, allowing for constraints, is solved utilizing this method. In each iteration, the finite element method provides the electric potential field within the model of the domain. An electrode model is also proposed (thus, increasing the accuracy of the finite element results). The algorithm is tested using numerically simulated data and also experimental data, and absolute resistivity values are obtained. These results, corresponding to phantoms with two different conductive materials, exhibit relatively well-defined boundaries between them, and show that this is a practical and potentially useful technique to be applied to monitor lung aeration, including the possibility of imaging a pneumothorax.

Estudos numéricos para o problema da tomografia por impedância elétrica; Numerical studies for the problem of electric impedance tomography

Aguilar, Juan Carlos Zavaleta
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 11/03/2009 PT
Relevância na Pesquisa
56.38%
Este trabalho estuda a técnica de reconstrução de imagens conhecido como tomografia por impedância elétrica em um domínio bidimensional. Esta técnica consiste na alocação de eletrodos na fronteira do volume e uma fonte injeta padrões de corrente através dos eletrodos e medem-se as voltagens resultantes na fronteira. Com estes dados estima-se a condutividade (ou resistividade) do interior do domínio criando-se uma imagem do mesmo. A tomografia por impedância elétrica é um problema inverso e mal posto no sentido de Hadamard. Estudam-se diversos métodos de solução para resolver o problema direto usando métodos numéricos como diferenças finitas e volumes finitos. Proporemos os métodos numéricos a serem aplicados na solução do problema direto os quais serão testados com problemas onde a solução analítica é conhecida. Posteriormente aplicaremos os métodos propostos ao problema especifico. Uma questão importante na reconstrução de imagens é propor a maneira como aproximar o Jacobiano (ou matriz de sensibilidade) do problema, assim desenvolvemos uma técnica para a aproximação do mesmo usando os dados fornecidos pelo problema direto.; In this work is studied the technique of reconstruction of images known as electrical impedance tomography for a two-dimensional domain. This technique consists in the allocation of electrodes on the border of the volume and a source injects patterns of current through the electrodes and then measuring voltages through the other electrodes. With these data it is estimated the conductivity (or resistivity) on the interior of the domain and an image is create of it. The electrical impedance tomography is an inverse and ill conditioned problem in the Hadamard sense. In this work...

Estudo da influência do esforço e da posição corporal no esvaziamento pulmonar regional em indivíduos saudáveis por meio da tomografia de impedância elétrica; Effect of effort and posture on regional lung emptying in healthy subjects detected by electric impedance tomography

Torsani, Vinicius
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 19/03/2009 PT
Relevância na Pesquisa
46.32%
A Tomografia de Impedância Elétrica (TIE) é um método de imagem que permite estudarmos alterações regionais de ventilação pulmonar com alta resolução temporal. Estudamos a influência da posição corporal e do esforço expiratório no esvaziamento regional pulmonar comparando dados de espirometria com os da TIE adquiridos simultaneamente. MÉTODOS: Oito voluntários monitorados continuamente com TIE, realizaram manobras de capacidade vital lenta (CVL) com washout de nitrogênio (WN2) e capacidade vital forçada (CVF) nas posições sentado, decúbito lateral direito (DLD) e esquerdo (DLE). Em todas as posições, comparamos a variação global de impedância (Z) com os volumes da espirometria. Analisamos também as variações regionais de volume do pulmão direito e esquerdo, em cada posição, e a cada 10% da expiração total através da TIE; estes dados foram comparados com análise do WN2. RESULTADOS: Na espirometria e na TIE, houve uma redução no volume total expirado na CVF e na CVL dos decúbitos laterais quando comparados à posição sentada (P = 0,001). Na análise da CVL através da TIE, observamos um fluxo maior no pulmão dependente (de 2 a 10 vezes maior), em ambos os decúbitos laterais, com inversão deste padrão aproximadamente na metade da capacidade vital. Já na CVF o Z foi semelhante entre os pulmões ao longo da expiração...

A influência do Ferro e do óxido de Cério sobre a condutividade elétrica e a resistência à corrosão do Alumínio Anodizado; The iron and cerium oxide influence on the electric conductivity and the corrosion resistance of anodized aluminum

Souza, Kellie Provazi de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 16/05/2006 PT
Relevância na Pesquisa
46.47%
Investiga-se a influência de diferentes tratamentos sobre o sistema alumínio com cobertura de óxido de alumínio. A anodização do alumínio em meio de ácido sulfúrico e meio misto de sulfúrico e fosfórico foi empregada para alterar a resistência à corrosão, a espessura, o grau de cobertura e a microdureza do óxido anódico; e a eletrodeposição de ferro no interior óxido anódico em meio de sulfato com tratamento químico de selagem com cério, para alterar a sua condutividade elétrica e a sua resistência à corrosão. Para a eletrodeposição de ferro aplicou-se corrente contínua e pulsada e diversificou-se a composição do eletrólito de Fe(SO4)2(NH4)2.6H2O, com a adição dos ácidos bórico e ascórbico e para o tratamento de selagem, variou-se a concentração do CeCl3. A espectroscopia de energia dispersiva de raios X (EDS), a fluorescência de raios X (FRX) e a análise morfológica por microscopia eletrônica de varredura (MEV) permitiram verificar que, a corrente pulsada eleva o teor de ferro na camada anódica e a presença dos aditivos inibe a oxidação do ferro. As curvas cronopotenciométricas obtidas durante a eletrodeposição de ferro indicaram que a mistura dos ácidos bórico e ascórbico aumentaram a eficiência do processo de eletrodeposição. A espectroscopia de impedância eletroquímica (EIE)...

Structural FRF acquisition via electric impedance measurement applied to damage location

Lopes, V; Pereira, J. A.; Inman, D. J.; SEM
Fonte: Soc Experimental Mechanics Inc Publicador: Soc Experimental Mechanics Inc
Tipo: Conferência ou Objeto de Conferência Formato: 1549-1555
ENG
Relevância na Pesquisa
46.45%
Continuing development of new materials makes systems lighter and stronger permitting more complex systems to provide more functionality and flexibility that demands a more effective evaluation of their structural health. Smart material technology has become an area of increasing interest in this field. The combination of smart materials and artificial neural networks can be used as an excellent tool for pattern recognition, turning their application adequate for monitoring and fault classification of equipment and structures. In order to identify the fault, the neural network must be trained using a set of solutions to its corresponding forward Variational problem. After the training process, the net can successfully solve the inverse variational problem in the context of monitoring and fault detection because of their pattern recognition and interpolation capabilities. The use of structural frequency response function is a fundamental portion of structural dynamic analysis, and it can be extracted from measured electric impedance through the electromechanical interaction of a piezoceramic and a structure. In this paper we use the FRF obtained by a mathematical model (FEM) in order to generate the training data for the neural networks...

Detecção de falhas em estruturas inteligentes usando otimização por nuvem de partículas: fundamentos e estudo de casos

Tebaldi, Adriano; Coelho, Leandro dos Santos; Lopes Junior, Vicente
Fonte: Sociedade Brasileira de Automática Publicador: Sociedade Brasileira de Automática
Tipo: Artigo de Revista Científica Formato: 312-330
POR
Relevância na Pesquisa
46.44%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Os materiais piezelétricos são denominados de materiais inteligentes e pertencem a uma classe de dielétricos que exibem deformação significativa em resposta a aplicação de um campo elétrico. Estes materiais, também, produzem uma polarização dielétrica, ou seja, um campo elétrico em resposta a deformação no material. Esta dupla propriedade exibida pelos materiais piezelétricos torna extremamente vantajosa a aplicação destes materiais para sistemas de controle e para localização e caracterização de falhas estruturais. Neste artigo, a caracterização de falhas estruturais é realizada em dois passos. em uma primeira etapa é utilizado o método da impedância elétrica para se determinar a região do dano e em uma segunda etapa se utiliza um método de otimização para quantificar a severidade das falhas. Identificação de falhas pertence ao grupo de problemas inversos, e portanto, não há solução única. A metodologia híbrida proposta se beneficia da técnica de impedância elétrica para localizar as regiões de danos e, assim, diminuir o número de variáveis envolvidas no processo de otimização. O procedimento é validado através de diferentes abordagens de otimização por nuvem de partículas...

Impedance-based structural health monitoring with artificial neural networks

Lopes Jr., Vicente; Park, Gyuhae; Cudney, Harley H.; Inman, Daniel J.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 206-214
ENG
Relevância na Pesquisa
46.31%
This paper presents a non-model based technique to detect, locate, and characterize structural damage by combining the impedance-based structural health monitoring technique with an artificial neural network. The impedance-based structural health monitoring technique, which utilizes the electromechanical coupling property of piezoelectric materials, has shown engineering feasibility in a variety of practical field applications. Relying on high frequency structural excitations (typically >30 kHz), this technique is very sensitive to minor structural changes in the near field of the piezoelectric sensors. In order to quantitatively assess the state of structures, multiple sets of artificial neural networks, which utilize measured electrical impedance signals for input patterns, were developed. By employing high frequency ranges and by incorporating neural network features, this technique is able to detect the damage in its early stage and to estimate the nature of damage without prior knowledge of the model of structures. The paper concludes with experimental examples, investigations on a massive quarter scale model of a steel bridge section and a space truss structure, in order to verify the performance of this proposed methodology.

Fractal approach to ac impedance spectroscopy studies of ceramic materials

Branković, Goran; Branković, Zorica; Jović, Vladimir D.; Varela, José Arana
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 89-94
ENG
Relevância na Pesquisa
46.42%
A novel fractal model for grain boundary regions of ceramic materials was developed. The model considers laterally inhomogeneous distribution of charge carriers in the vicinity of grain boundaries as the main cause of the non-Debye behaviour and distribution of relaxation times in ceramic materials. Considering the equivalent circuit the impedance of the grain boundary region was expressed. It was shown that the impedance of the grain boundary region has the form of the Davidson-Cole equation. The fractal dimension of the inhomogeneous distribution of charge carriers in the region close to the grain boundaries could be calculated based on the relation ds = 1 + β, where β is the constant from the Davidson-Cole equation.

FINITE ELEMENT SIMULATIONS FOR THE COMPREHENSION OF PHYSICAL PHENOMENA INVOLVED IN ELECTRIC IMPEDANCE TOMOGRAPHY OF MASONRY STRUCTURES

Naasson, Alcantara; Ramos Luis, F.; Paulo, Mendes; Joao, Ferreira; Francisco, Fernandes; Lourenco Paulo, B.; Jasienko, J.
Fonte: Dolnoslaskie Wydawnictwo Edukacyjne-dwe Publicador: Dolnoslaskie Wydawnictwo Edukacyjne-dwe
Tipo: Conferência ou Objeto de Conferência Formato: 2271-2279
ENG
Relevância na Pesquisa
56.32%
The paper describes the preliminary studies of University of Minho on the use of Electric Impedance/Resistance Tomography to assess masonry structures. The study is focused on the analysis of values of current and voltage resulting from the use of an electrical source with voltage and frequency values from a distribution network. The analysis is made from results obtained through computer simulations, using a three-dimensional model of the idealized masonry structures. A finite element program was used for the simulations. Three types of electrodes were used in simulations, and the analysis of the results led to significant conclusions. Later masonry specimens were built and a series of preliminary tests were carried out in the laboratory. The comparative analysis of simulated and experimental results allowed identifying the factors that have influence on the physical results.

ELECTRIC IMPEDANCE OF SUSPENSIONS OF SPHERES

Cole, Kenneth S.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 20/09/1928 EN
Relevância na Pesquisa
46.32%
A general expression has been derived for the electric impedance of a suspension of spheres each having a homogeneous non-reactive interior and a thin surface layer with both resistance and reactance. The applications and limitations of impedance measurements on such suspensions are discussed.

ELECTRIC IMPEDANCE OF SUSPENSIONS OF ARBACIA EGGS

Cole, Kenneth S.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 20/09/1928 EN
Relevância na Pesquisa
46.42%
Apparatus has been designed and constructed for the measurement of the electric impedance of suspensions of Arbacia eggs in sea water to alternating currents of frequencies from one thousand to fifteen million cycles per second. This apparatus is simple, rugged, compact, accurate, and rapid. The data lead to the conclusions that the specific resistance of the interior of the egg is about 90 ohm cm. or 3.6 times that of sea water, and that the impedance of the surface of the egg is probably similar to that of a "polarization capacity". The characteristics of this surface impedance can best be determined by measurements of the capacity and resistance of suspensions of eggs. No specific change has been found in the interior resistance or the surface impedance which can be related either to membrane formation or to cell division.

An electric impedance based microelectromechanical system flow sensor for ionic solutions

Ayliffe, H Edward; Rabbitt, RD
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/2003 EN
Relevância na Pesquisa
46.32%
Microfluidic devices with channel cross sections measuring 4 × 10 μm2 instrumented with gold microelectrodes were used to sense flow rates of ionic solutions on the basis of electric impedance (EI) measured perpendicular to the flow. Negative pressures were applied to access ports of the microdevices to generate flow of saline solutions (physiologic concentrations 0.9%) through the micro-EI recording zone with flow rates between 2.4 and 4.8 μl min−1. The EI spectra (100 Hz–20 MHz) recorded under flow conditions were compared with the no-flow condition. Changes in the magnitude of EI (at 350 Hz) for flow rates as low as 2.4 μl min−1 were statistically significant compared with the no-flow condition. The observed dependence of EI on flow rate is attributed to the relative difference between the rate of migration of charge-balancing electrolyte ions to the electrode surface and the rate of removal of the same ions by forced convection. An electrochemical convection–diffusion model was used to study the observed dependence on flow. Simulations support the conceptual model that passing DC current from the gold electrodes into the ionic solution results in an increase in ionic concentration near the electrode surface (due to the inward migration of counter-balancing ions). When the fluid flow rates increase...

Single cell electric impedance topography: Mapping membrane capacitance

Dharia, Sameera; Ayliffe, Harold E.; Rabbitt, Richard D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.45%
Single-cell electric impedance topography (sceTopo), a technique introduced here, maps the spatial distribution of capacitance (i.e. displacement current) associated with the membranes of isolated, living cells. Cells were positioned in the center of a circular recording chamber surrounded by eight electrodes. Electrodes were evenly distributed on the periphery of the recording chamber. Electric impedance measured between adjacent electrode pairs (10 kHz–5 MHz) was used to construct topographical maps of the spatial distribution of membrane capacitance. Xenopus Oocytes were used as a model cell to develop sceTopo because these cells consist of two visually distinguishable hemispheres, each with distinct membrane composition and structure. Results showed significant differences in the imaginary component of the impedance between the two oocyte hemispheres. In addition, the same circumferential array was used to map the size of the extracellular electrical shunt path around the cell, providing a means to estimate the location and shape of the cell in the recording chamber.

Real-time monitoring of flavivirus induced cytopathogenesis using cell electric impedance technology

Fang, Ying; Ye, Peifang; Wang, Xiaobo; Xu, Xiao; Reisen, William
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.38%
A real-time cell analysis (RTCA) system based on cell-substrate electric impedance technology was used to monitor cytopathic effects (CPE) in Vero cell cultures infected with West Nile virus (WNV) and St. Louis encephalitis virus (SLEV) at infectious doses ranging from 101 to 106 plaque forming units (PFU) of virus. A kinetic parameter characterizing virus-induced CPE, CIT50 or the time to 50% decrease in cell impedance, was inversely proportional to virus infectious dose. In WNV-infected cells, the onset and rate of CPE was earlier and faster than in SLEV-infected cells, which was consistent with viral cytolytic activity. A mathematical model simulating impedance-based CPE kinetic curves indicated that the replication rate of WNV was about 3 times faster than SLEV. The RTCA system also was used for quantifying the level of cell protection by specific neutralizing antibodies against WNV and SLEV. The onset of WNV or SLEV-induced CPE was delayed in the presence of specific anti-sera, and this delay in the CIT50 was well correlated with the titer of the neutralizing antibody as measured independently by plaque reduction neutralization tests (PRNT). The RTCA system provided a high throughput and quantitative method for real-time monitoring viral growth in cell culture and its inhibition by neutralizing antibodies.

Electric Impedance Microflow Cytometry for Characterization of Cell Disease States†

Du, E; Ha, Sungjae; Diez-Silva, Monica; Dao, Ming; Suresh, Subra; Chandrakasan, Anantha P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 07/10/2013 EN
Relevância na Pesquisa
46.5%
The electrical properties of biological cells have connections to their pathological states. Here we present an electric impedance microflow cytometry (EIMC) platform for the characterization of disease states of single cells. This platform entails a microfluidic device for a label-free and non-invasive cell-counting assay through electric impedance sensing. We identified a dimensionless offset parameter δ obtained as a linear combination of a normalized phase shift and a normalized magnitude shift in electric impedance to differentiate cells on the basis of their pathological states. This paper discusses a representative case study on red blood cells (RBCs) invaded by Plasmodium falciparum malaria parasites. Invasion of P. falciparum induces physical and biochemical changes on the host cells throughout a 48-h multi-stage life cycle within the RBC. As a consequence, it also induces progressive changes in electrical properties of the host cells .We demonstrate that the EIMC system in combination with data analysis involving the new offset parameter allows differentiation of Pf–invaded RBCs from uninfected RBCs as well as among different P. falciparum intraerythrocytic asexual stages including the ring stage. The representative results provided here also point to the potential of the proposed experimental and analysis platform as a valuable tool for non-invasive diagnostics of a wide variety of disease states and for cell separation.

Upper esophageal sphincter impedance as a marker of sphincter opening diameter

Omari, T.; Ferris, L.; Dejaeger, E.; Tack, J.; Vanbeckevoort, D.; Rommel, N.
Fonte: Amer Physiological Soc Publicador: Amer Physiological Soc
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
Relevância na Pesquisa
46.39%
The measurement of the physical extent of opening of the upper esophageal sphincter (UES) during bolus swallowing has to date relied on videofluoroscopy. Theoretically luminal impedance measured during bolus flow should be influenced by luminal diameter. In this study, we measured the UES nadir impedance (lowest value of impedance) during bolus swallowing and assessed it as a potential correlate of UES diameter that can be determined nonradiologically. In 40 patients with dysphagia, bolus swallowing of liquids, semisolids, and solids was recorded with manometry, impedance, and videofluoroscopy. During swallows, the UES opening diameter (in the lateral fluoroscopic view) was measured and compared with automated impedance manometry (AIM)-derived swallow function variables and UES nadir impedance as well as high-resolution manometry-derived UES relaxation pressure variables. Of all measured variables, UES nadir impedance was the most strongly correlated with UES opening diameter. Narrower diameter correlated with higher impedance (r = −0.478, P < 0.001). Patients with <10 mm, 10–14 mm (normal), and ≥15 mm UES diameter had average UES nadir impedances of 498 ± 39 Ohms, 369 ± 31 Ohms, and 293 ± 17 Ohms, respectively (ANOVA P = 0.005). A higher swallow risk index...

Effect of bolus volume and viscosity on pharyngeal automated impedance manometry variables derived for broad dysphagia patients

Omari, T.; Dejaeger, E.; Tack, J.; Van Beckevoort, D.; Rommel, N.
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
46.33%
Automated impedance manometry (AIM) analysis measures swallow variables defining bolus timing, pressure, contractile vigour, and bolus presence, which are combined to derive a swallow risk index (SRI) correlating with aspiration. In a heterogeneous cohort of dysphagia patients, we assessed the impact of bolus volume and viscosity on AIM variables. We studied 40 patients (average age = 46 years). Swallowing of boluses was recorded with manometry, impedance, and videofluoroscopy. AIMplot software was used to derive functional variables: peak pressure (PeakP), pressure at nadir impedance (PNadImp), time from nadir impedance to peak pressure (TNadImp-PeakP), the interval of impedance drop in the distal pharynx (flow interval, FI), upper oesophageal sphincter (UES) relaxation interval (UES RI), nadir UES pressure (Nad UESP), UES intrabolus pressure (UES IBP), and UES resistance. The SRI was derived using the formula SRI = (FI * PNadImp)/(PeakP * (TNadImp-PeakP + 1)) * 100. A total of 173 liquid, 44 semisolid, and 33 solid boluses were analysed. The SRI was elevated in relation to aspiration. PeakP increased with volume. SRI was not significantly altered by bolus volume. PNadImp, UES IBP, and UES resistance increased with viscosity. SRI was lower with increased viscosity. In patients with dysphagia...

Optimal criteria for detecting bolus passage across the pharyngo-oesophageal segment during the normal swallow using intraluminal impedance recording

Szczesniak, M.; Rommel, N.; Dinning, P.; Fuentealba, S.; Cook, I.; Omari, T.
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
Publicado em //2008 EN
Relevância na Pesquisa
46.39%
The impedance criteria for the detection of the arrival of bolus head and clearance of bolus tail in the pharynx have not been defined, and may differ from accepted criteria used in the oesophagus. Our aim was to define the optimal impedance criteria that most accurately defined passage of the swallowed bolus moving through the pharyngo-oesophageal segment. In eight healthy volunteers, an assembly incorporating seven impedance-measuring segments was positioned across the pharyngo-oesophageal segment, and subjects swallowed liquid and semisolid radio-opaque boluses (2-20 mL) while impedance was simultaneously recorded with videofluoroscopic images. To derive the optimal criteria, in an iterative process we correlated impedance defined bolus presence with fluoroscopy (Cohen's Kappa) for a range of impedance cut-off values from 100% to 0% for both the initial fall, and recovery of impedance. Bolus presence in the pharynx, as determined by the 'standard' criteria (50% drop and recovery to 50% of baseline), correlated very modestly with videofluoroscopy (kappa approximately 0.35). The criteria that most accurately defined bolus passage varied between pharyngeal regions. Threshold (% of baseline) for bolus head entry into the region ranged from 71% to 80%. Threshold for bolus tail clearance varied from nadir to 19%. Correlation of impedance with videofluoroscopy improved to kappa approximately 0.6 with the above criteria. The impedance criteria defining bolus presence across the pharyngo-oesophageal segment differ from those adopted in the oesophagus. Pharyngeal impedance provides an accurate...

Assessment of oesophageal motor function using combined perfusion manometry and multi-channel intraluminal impedance measurement in normal subjects

Nguyen, Q.; Tippett, R.; Tippett, M.; Conchillo, J.; Smout, A.; Holloway, R.
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
Publicado em //2005 EN
Relevância na Pesquisa
46.36%
Multichannel intraluminal impedance (MII) is being used increasingly to assess oesophageal bolus clearance. However, there is no good standardization of the impedance parameters that define 'effective bolus clearance'. The aim of this study was to define these important impedance parameters and to determine their normal values. Concurrent perfusion manometry and MII were performed in 42 healthy volunteers. Ten, 5-mL liquid (saline) boluses and then, 10x5-mL low impedance viscous boluses were tested in each subject in the right-lateral position. Normal values for bolus presence time (BPT) at each site and total bolus transit time (TBTT) were determined from either 'normal' peristaltic responses (amplitude>or=30 mmHg in distal oesophagus) or 'super-normal' peristaltic responses (amplitudes>or=50 mmHg at all sites). The relationship between BPT and TBTT within a response and per-individual performance was determined. A total of 840 swallows of liquids and viscous responses were analysed. BPT and TBTT of viscous swallows were longer than those for liquids. Non-peristaltic responses were significantly more likely not to clear a viscous than a liquid bolus. Within a response, the number of sites with prolonged BPT strongly predicted the incidence of prolonged TBTT. Using impedance criteria...

A new method to improve the impedance of the CC-II's X input

Alves, L. N.; Aguiar, R.L.
Fonte: Institute of Electrical and Electronics Engineers (IEEE) Publicador: Institute of Electrical and Electronics Engineers (IEEE)
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
46.52%
This paper presents a new method to improve the CC-II's X input impedance. The new method applies a double feedback scheme comprising both, series-shunt negative and series-series positive feedback paths. This method achieves input impedance levels below -15dBΩ (comparable to other reported methods), with controlled frequency peaking. Simulation results compare frequency performance of the proposed method with other reported methods, using the same reference CC-II. Effects of feedback on current and voltage transfers of the CC-II are also discussed, pointing to limitation factors on impedance reduction. ©2004 IEEE.