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Reference distribution of the bioelectrical impedance vector in healthy term newborns

MARGUTTI, Ana V. B.; MONTEIRO, Jacqueline P.; CAMELO JR., Jose S.
Fonte: CAMBRIDGE UNIV PRESS Publicador: CAMBRIDGE UNIV PRESS
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.9%
Bioelectrical impedance vector analysis (BIVA) is a new method that is used for the routine monitoring of the variation in body fluids and nutritional status with assumptions regarding body composition values. The aim of the present study was to determine bivariate tolerance intervals of the whole-body impedance vector and to describe phase angle (PA) values for healthy term newborns aged 7-28 d. This descriptive cross-sectional study was conducted on healthy term neonates born at a low-risk public maternity. General and anthropometric neonatal data and bioelectrical impedance data (800 mu A-50 kHz) were obtained. Bivariate vector analysis was conducted with the resistance-reactance (RXc) graph method. The BIVA software was used to construct the graphs. The study was conducted on 109 neonates (52.3% females) who were born at term, adequate for gestational age, exclusively breast-fed and aged 13 (SD 3.6) d. We constructed one standard, reference, RXc-score graph and RXc-tolerance ellipses (50, 75 and 95 %) that can be used with any analyser. Mean PA was 3.14 (SD 0.43)degrees (3.12 (SD 0.39)degrees for males and 3.17 (SD 0.48)degrees for females). Considering the overlapping of ellipses of males and females with the general distribution...

Image Reconstruction Using Interval Simulated Annealing in Electrical Impedance Tomography

Martins, Thiago de Castro; Camargo, Erick Dario León Bueno de; Lima, Raul Gonzalez; Amato, Marcelo Britto Passos; Tsuzuki, Marcos de Sales Guerra
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC; Piscataway Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC; Piscataway
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.9%
Electrical impedance tomography (EIT) is an imaging technique that attempts to reconstruct the impedance distribution inside an object from the impedance between electrodes placed on the object surface. The EIT reconstruction problem can be approached as a nonlinear nonconvex optimization problem in which one tries to maximize the matching between a simulated impedance problem and the observed data. This nonlinear optimization problem is often ill-posed, and not very suited to methods that evaluate derivatives of the objective function. It may be approached by simulated annealing (SA), but at a large computational cost due to the expensive evaluation process of the objective function, which involves a full simulation of the impedance problem at each iteration. A variation of SA is proposed in which the objective function is evaluated only partially, while ensuring boundaries on the behavior of the modified algorithm.; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP); Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2009/07173-2, 2010/19380-0, 2009/14699-0]; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico [304.258/2007-5, 309.570/2010-7]; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico

Bioelectrical impedance analysis and anthropometry for the determination of body composition in rats: effects of high-fat and high-sucrose diets; Bioimpedância elétrica e antropometria na determinação da composição corporal de ratos: efeitos das dietas ricas em lipídeos e sacarose

Angéloco, Larissa Rodrigues Neto; Deminice, Rafael; Leme, Izabel de Arruda; Lataro, Renata Cristina; Jordao Junior, Alceu Afonso
Fonte: PONTIFICIA UNIVERSIDADE CATOLICA CAMPINAS; CAMPINAS Publicador: PONTIFICIA UNIVERSIDADE CATOLICA CAMPINAS; CAMPINAS
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.9%
Objective The aim of the present study was to determine the impedance of Wistar rats treated with high-fat and high-sucrose diets and correlate their biochemical and anthropometric parameters with chemical analysis of the carcass. Methods Twenty-four male Wistar rats were fed a standard (AIN-93), high-fat (50% fat) or high-sucrose (59% of sucrose) diet for 4 weeks. Abdominal and thoracic circumference and body length were measured. Bioelectrical impedance analysis was used to determine resistance and reactance. Final body composition was determined by chemical analysis. Results Higher fat intake led to a high percentage of liver fat and cholesterol and low total body water in the High-Fat group, but these changes in the biochemical profile were not reflected by the anthropometric measurements or bioelectrical impedance analysis variables. Anthropometric and bioelectrical impedance analysis changes were not observed in the High-Sucrose group. However, a positive association was found between body fat and three anthropometric variables: body mass index, Lee index and abdominal circumference. Conclusion Bioelectrical impedance analysis did not prove to be sensitive for detecting changes in body composition, but body mass index, Lee index and abdominal circumference can be used for estimating the body composition of rats.; OBJETIVO: Determinar a impedância de ratos tratados com dietas ricas em lipídeos e sacarose por meio do método da bioimpedância elétrica e correlacionar com a análise direta da carcaça...

Avaliação da ventilação mecânica controlada a pressão utilizando-se a técnica de tomografia por impedância elétrica durante anestesia geral em cães; Evaluation of pressure-controlled ventilation using the technique of electrical impedance tomography during general anesthesia in dogs

Kamakura, Tatiana Paula Alvarenga de Carvalho
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 13/12/2013 PT
Relevância na Pesquisa
36.96%
A hipoventilação secundária ao procedimento anestésico é comum na prática anestésica, e, sendo assim, o emprego de técnicas de ventilação mecânica é adotado como forma de minimizar e/ou evitar os efeitos deletérios da hipoventilação. Porém, o uso de ventiladores mecânicos não é isento de risco, e atelectasias podem se formar mesmo quando são utilizados. Para análise em tempo real do pulmão, a técnica de tomografia por impedância elétrica vem sendo empregada em conjunto com outros meios de monitoração, tendo se demonstrado um meio útil de avaliação da ventilação pulmonar de maneira não invasiva, passível de ser utilizada à beira do leito e sem emissão de radiação. Estudos utilizando o tomógrafo de impedância elétrica em cães são escassos. O objetivo desse trabalho foi avaliar a ventilação de cães submetidos à anestesia inalatória e à ventilação mecânica utilizando a técnica de tomografia por impedância elétrica. Foram utilizados onze cães com peso superior a 16 kg e classificados como baixo risco anestésico (ASA I ou II). Os animais receberam acepromazina e meperidina como medicação pré-anestésica, propofol como indutor e isofluorano na manutenção da anestesia. Foram mantidos em ventilação mecânica controlada a pressão...

A New Impedance Measurement System for PZT-Based Structural Health Monitoring

Baptista, Fabricio Guimaraes; Vieira Filho, Jozué
Fonte: Institute of Electrical and Electronics Engineers (IEEE) Publicador: Institute of Electrical and Electronics Engineers (IEEE)
Tipo: Artigo de Revista Científica Formato: 3602-3608
ENG
Relevância na Pesquisa
36.99%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Recent research has shown that electromechanical (E/M) impedance-based techniques are an efficient strategy for damage sensing in the context of structural health monitoring (SHM). The basic principle is to excite the lead zirconate titanate (PZT) sensors attached to the structure and to measure the corresponding electrical impedance. A variation in the electrical impedance indicates a variation in the mechanical impedance and, consequently, structural damage. To measure the electrical impedance, most universities and research centers use expensive, bulky, heavy, and high-powered impedance analyzers, which limit new developments and practical applications. To overcome these issues, this paper presents an efficient and inexpensive methodology for electrical impedance measurement. To verify the efficiency and accuracy of the new methodology, practical tests were carried out, and the results were compared with those obtained using a conventional impedance analyzer.

Avaliação dos Impactos da Impedância de Falta e da Geração Distribuída em Estudos de Afundamentos de Tensão; Impact Assessment of Fault Impedance and Distributed Generation Studies of Voltage Sags

RAMOS, Alessandro Candido Lopes
Fonte: Universidade Federal de Goiás; BR; UFG; Mestrado em Engenharia Elétrica e de Computação; Engenharia Publicador: Universidade Federal de Goiás; BR; UFG; Mestrado em Engenharia Elétrica e de Computação; Engenharia
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
36.93%
This work presents an impact analysis of the fault impedance and distributed ge- neration on the amplitude and annual average quantity of voltage sags in sensitive end-users. Phase-to-ground solid and non-solid faults were simulated in 62 transmission lines at 230, 138, 69 and 13.8 kV, which made part of the electrical system of the municipality of Goiânia, the capital city of the Goiás State, Brazil. For each fault position, a resistive fault impedance was considered. This impedance was considered equal to 0, 2, 5, 10, or 15  or even random. In this case, each one of the mentioned impedance values has a specific probability to occur. The voltage-behind-reactance synchronous machine model was used to model the distributed generation units. The analysis here described is based on simulation results obtained through the Fault Position Method in combination with the Monte Carlo Method. The faults were si-mulated through a frequency-domain fault simulation software called ANAFAS. In order to overcome some limitations and increase the flexibility of the simulation tool, a computational program, called ANAFAS-GUI, was developed in Java language. This program allows the automatic simulation of several cases, with different fault characteristics...

Monitoramento de integridade estrutural de materiais compostos sujeitos a impactos empregando a técnica da impedância eletromecânica; Structural health monitoring of composite materials subjected to impacts using the electromechanical impedance technique

Tsuruta, Karina Mayumi
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
Relevância na Pesquisa
36.96%
Atualmente, os materiais compostos vêm substituindo os materiais tradicionais, principalmente em aplicações que exigem melhor desempenho, segurança, economia e durabilidade. No entanto, estes materiais apresentam mecanismos de dano complexos que podem ser difíceis de detectar em estágios iniciais. Os danos podem ocorrer durante a fabricação ou utilização, ou mesmo durante a manutenção. Em estruturas aeronáuticas, as maiores causas de dano estão ligadas a objetos que colidem com a estrutura, como a colisão de pássaros, granizo, pedras na pista de pouso/decolagem e por ferramentas durante a manutenção. Em vista disto, é grande o interesse em detectar danos incipientes provocados por impactos em componentes estruturais constituídos de materiais compostos. Neste contexto, o objetivo deste trabalho é o de avaliar o uso de uma técnica de monitoramento de integridade estrutural baseada no conceito de impedância eletromecânica para a detecção e quantificação de danos causados por impactos de baixa energia em placas de material composto. O método da impedância eletromecânica é uma técnica não destrutiva que utiliza o acoplamento eletromecânico de materiais piezelétrico colados à superficie da estrutura monitorada. A metodologia adotada consiste em realizar impactos em corpos de prova de materiais compostos empregando um dispositivo pendular ad hoc que permite obter diversos valores da energia de impacto. Para cada corpo de prova...

Técnicas de inteligência artificial aplicadas ao método de monitoramento de integridade estrutural baseado na impedância eletromecânica para monitoramento de danos em estruturas aeronáuticas; Artificial intelligence techniques applied to the impedance-based structural health monitoring technique for monitoring damage in aircraft structures

Palomino, Lizeth Vargas
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Tese de Doutorado
POR
Relevância na Pesquisa
37.05%
O conceito básico da técnica de integridade estrutural baseada na impedância tem a ver com o monitoramento da variação da impedância eletromecânica da estrutura, causada pela presença alterações estruturais, através de pastilhas de material piezelétrico coladas na superfície da estrutura ou nela incorporadas. A impedância medida se relaciona com a impedância mecânica da estrutura. A partir da variação dos sinais de impedância pode-se concluir pela existência ou não de uma falha. Para quantificar esta falha, métricas de dano são especialmente definidas, permitindo atribuir-lhe um valor escalar característico. Este trabalho pretende inicialmente avaliar a influência de algumas condições ambientais, tais como os campos magnéticos e os meios iônicos na medição de impedância. Os resultados obtidos mostram que os campos magnéticos não tem influência na medição de impedância e que os meios iônicos influenciam os resultados; entretanto, ao blindar o sensor, este efeito se reduz consideravelmente. Também foi estudada a influencia da geometria, ou seja, do formato do PZT e da posição do sensor com respeito ao dano. Verificou-se que o formato do PZT não tem nenhuma influência na medição e que a posição do sensor é importante para detectar corretamente o dano. Neste trabalho se apresenta o desenvolvimento de um sistema de medição de impedância de baixo custo e portátil que tem a capacidade de medir e armazenar a medição de 16 PZTs sem a necessidade de intervenção humana. Um aspecto de fundamental importância no contexto deste trabalho é a caracterização do dano a partir dos sinais de impedância coletados. Neste sentido...

Characterization of intraluminal impedance patterns associated with gas reflux in healthy volunteers

van Wijk, M.; Sifrim, D.; Rommel, N.; Benninga, M.; Davidson, G.; Omari, T.
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
Relevância na Pesquisa
36.96%
Multichannel intraluminal impedance (MII) recording allows assessment of flow through the oesophagus and differentiation between liquid and gas contents. Existing MII criteria for recognition of gas gastro-oesophageal reflux (GOR) have not been validated during known gas GOR in humans. Aims: (i) Characterize MII patterns of known gas GOR and optimize criteria. (ii) Clarify interrelationships between magnitude of maximal impedance change, luminal diameter and electrode-mucosa contact. Ten healthy volunteers (six male, 21–37 years) were studied using an oesophageal MII-manometry catheter. After catheter placement, subjects were asked to drink 600 mL of carbonated soft drink. Recordings were made for 20 min and the protocol repeated. Reported belches confirmed manometrically (triggered by transient lower oesophageal sphincter relaxations) were included for analysis. Those episodes were compared against commonly used criteria. Another five subjects (three male, 26–52 years) underwent simultaneous MII and videofluoroscopy using the same protocol. Videofluoroscopic images were analyzed for luminal diameter and the presence of electrode–mucosa contact. All analyzed gas GOR episodes (n = 88) were associated with a pattern of impedance rise which was either retrograde (62.5%)...

Impact of bolus volume on small intestinal intra-luminal impedance in healthy subjects

Nguyen, Q.; Bryant, L.; Burgstad, C.; Fraser, R.; Sifrim, D.; Holloway, R.
Fonte: W J G Press Publicador: W J G Press
Tipo: Artigo de Revista Científica
Publicado em //2010 EN
Relevância na Pesquisa
37.05%
AIM: To assess the impact of bolus volume on the characteristics of small intestinal (SI) impedance signals. METHODS: Concurrent SI manometry-impedance measurements were performed on 12 healthy volunteers to assess the pattern of proximal jejunal fluid bolus movement over a 14 cm-segment. Each subject was given 34 boluses of normal saline (volume from 1 to 30 mL) via the feeding tube placed immediately above the proximal margin of the studied segment. A bolus-induced impedance event occurred if there was > 12% impedance drop from baseline, over ≥ 3 consecutive segments within 10 s of bolus injection. A minor or major impedance event was defined as a duration of impedance drop < 60 s or ≥ 60 s, respectively. RESULTS: The minimum volume required for a detectable SI impedance event was 2 mL. A direct linear relationship between the SI bolus volume and the occurrence of impedance events was noted until SI bolus volume reached 10 mL, a volume which always produced an impedance flow event. There was a moderate correlation between the bolus volume and the duration of impedance drop (r = 0.63, P < 0.0001) and the number of propagated channels (r = 0.50, P < 0.0001). High volume boluses were associated with more major impedance events (≥ 10 mL boluses = 63%...

Pharyngeal flow interval: a novel impedance-based parameter correlating with aspiration

Noll, L.; Rommel, N.; Davidson, G.; Omari, T.
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
36.93%
BACKGROUND: The role of pharyngeal impedance recording for assessing pharyngeal function is yet to be established. The aim of this study was to evaluate impedance flow interval, a novel parameter, in relation to bolus residue and the occurrence of aspiration. The effect of catheter configuration was also assessed. METHODS: We studied 12 children (1.8-13.5years) with cerebral palsy, who were all referred for a videofluoroscopy due to suspected aspiration risk. Pharyngeal impedance patterns during bolus swallowing were recorded simultaneously with fluoroscopy. Two different catheter configurations were used: Catheter 1, 1.9mm diameter with 1cm electrodes and Catheter 2, 3.2mm diameter with 2cm electrodes. The flow interval was based on the objective assessment of impedance drop and recovery across multiple impedance segments and was correlated with fluoroscopic evidence of postswallow bolus residue and deglutitive aspiration. KEY RESULTS: One hundred and thirty two liquid swallows were evaluated. Patient swallows with aspiration compared to those without aspiration had a longer flow interval (Cath 1 P=0.005; Cath 2 P<0.001). Patient swallows with residue had a longer flow interval, however this was only significant for swallows recorded using Catheter 2 (P=0.004). Multiple logistic regressions showed that higher flow interval was a better marker of the presence of aspiration [odds ratio (OR) 13.4 (3.0...

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
37.02%
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...

Esophageal impedance baselines in infants before and after placebo and proton pump inhibitor therapy

Loots, C.; Wijnakker, R.; van Wijk, M.; Davidson, G.; Benninga, M.; Omari, T.
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
Relevância na Pesquisa
36.96%
BACKGROUND: Esophageal impedance monitoring records changes in conductivity. During esophageal rest, impedance baseline values may represent mucosal integrity. The aim of this study was to assess the influence of acid suppression on impedance baselines in a placebo-controlled setting. METHODS: Impedance recordings from 40 infants (0-6 months) enrolled in randomized placebo-controlled trials of proton pump inhibitor (PPI) were retrospectively analyzed. Infants underwent 24 h pH-impedance monitoring prior to and after 2 weeks of double blind therapy with placebo or a PPI. Typical clinical signs of gastro-esophageal reflux (GER) were recorded and I-GERQ-R questionnaire was completed. KEY RESULTS: Median (IQR) impedance baseline increased on PPI treatment (from 1217 (826-1514) to 1903 (1560-2194) Ω, P < 0.001) but not with placebo (from 1445 (1033-1791) to 1650 (1292-1983) Ω, P = 0.13). Baselines before treatment inversely correlate with the number of GER, acid GER, weakly acid GER, acid exposure, and symptoms. The change in baseline on treatment inversely correlates with acid exposure and acid GER. Patients with initial low baselines have no improved symptomatic response to treatment. CONCLUSIONS & INFERENCES: Impedance baselines are influenced by GER and increase significantly more with PPI therapy than with placebo. Clinical impact of this observation remains undefined as targeting therapy at infants with low baselines does not improve symptomatic response to treatment.; C. M. Loots...

Global sensitivity analysis of impedance measurement algorithms implememented in intelligent electronic devices.

Rohadi, Nanang
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2013
Relevância na Pesquisa
36.99%
A novel methodology for testing performance of impedance measurement algorithms used in transmission line protection schemes is developed. Nowadays, impedance measurement algorithms are software functions implemented in the multifunction Intelligence Electronic Devices (IEDs) responsible for overall monitoring, protection and control of transmission lines. Accurate impedance measurement during fault conditions is the key in successful performance of the line protection as well as fault location functions of an IED. This thesis investigates a typical practical situation where only short-term fault records of voltage and current measurements from one side of a transmission line are used as inputs in the impedance measurement algorithm. Current flowing into the fault from the remote terminal of transmission line as well as fault impedance can influence significantly accuracy of impedance measurement. Since these two quantities are not measured, we require a systematic tool which will assess sensitivity of impedance measurement to those factors. At present, these sensitivities are obtained in heuristic and ad hoc manner during application testing done by utilities before commissioning of new IEDs. Situation in practice can be increasingly complex and this kind of unsystematic testing approach can fail. The thesis addresses those practical complex cases in the systematic manner. In these cases we encounter the following configurations of transmission lines with new not measured factors: - parallel closely spaced lines...

Electrical impedance of Shiraz berries correlates with decreasing cell vitality during ripening

Caravia, L.; Collins, C.; Tyerman, S.D.
Fonte: Wiley Publicador: Wiley
Tipo: Artigo de Revista Científica
Publicado em //2015 EN
Relevância na Pesquisa
36.93%
BACKGROUND AND AIMS: Cell death in the mesocarp of Shiraz berries has been correlated with berry mass loss that occurs late in ripening and can be linked to berry composition. The current techniques to assess the level of berry cell disruption are time-consuming and can give only relative measures. Here we test if electrical impedance of the berry, which is a function of the state of cells within, can be used to detect the loss of cell vitality. METHODS AND RESULTS: Shiraz berries (774 berries) from two locations (one of them over two seasons) from veraison to harvest were studied. Electrical impedance spectroscopy was performed between 100 Hz and 1 or 2 MHz of alternating current across the berry, while for each berry proportion living tissue was estimated with fluorescein diacetate. The results indicated that, from veraison to the onset of cell death, berry impedance follows the accumulation of TSS. Thereafter, impedance decreases proportionally to the extent of berry cell death. CONCLUSIONS: Changes in cell vitality of the Shiraz grape berry can be objectively determined through impedance spectroscopy. The measurements also indicate that cell membranes, although becoming leaky, may still remain intact. SIGNIFICANCE OF THE STUDY: Impedance spectroscopy as applied to the grape berry has demonstrated a promising application for measuring berry composition; L. Caravia...

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
37.02%
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
36.96%
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...

Intraluminal impedance detects failure of pharyngeal bolus clearance during swallowing: a validation study in adults with dysphagia

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 //2009 EN
Relevância na Pesquisa
36.99%
Multichannel intraluminal impedance (MII) detects bolus flow through a healthy pharynx. The aim of this study was to determine whether the technique detects bolus flow and retention in patients with pharyngeal dysphagia; develop appropriate impedance-based criteria for assessing patients and to provide some preliminary insights into the clinical utility of the technique. Pharyngo-oesophageal pressure and impedance were recorded simultaneously with videofluoroscopy (VF) during swallows in six patients with dysphagia. Agreement, as to the presence or absence of bolus material, between the VF and MII was expressed using the Cohen's Kappa statistic. To test whether the impedance criteria for the detection of bolus passage in dysphagia could be improved, a Kappa statistic was calculated in an iterative process for a range of impedance values (100%-0%) defining bolus head entry and bolus tail clearance from the pharynx. Bolus presence according to the MII criteria previously derived by us in healthy controls demonstrated a modest correlation with VF when applied to this dysphagia population [0.37, 0.5 and 0.58 in the hypopharynx, upper oesophageal sphincter (UOS) and proximal oesophagus respectively]. In the patient population, the optimal impedance criteria were 50% for bolus head entry and 20% for bolus tail clearance. Adopting these criteria demonstrated enhanced agreement between VF and impedance; yielding Kappa coefficients of 0.42 in the hypopharynx...

Use of cellular impedance to characterize ligand functional selectivity at G protein-coupled receptors

Stallaert, Wayne
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
EN
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Les récepteurs couplés aux protéines G (RCPGs) représentent la plus grande famille de cibles thérapeutiques pour le traitement d’une panoplie de pathologies humaines. Bien que plusieurs décennies de recherche aient permis de façonner nos connaissances sur ces protéines membranaires, notre compréhension des déterminants moléculaires de leur activité signalétique reste encore limitée. De ces domaines de recherche, une avancée récente a mis à jour un nouveau phénomène, appelé sélectivité fonctionnelle des ligands, qui a bouleversé les paradigmes décrivant leu fonctionnement de ces récepteurs. Ce concept émane d’observations montrant que l’activité pharmacologique de certains ligands n’est pas nécessairement conservée sur tout le répertoire signalétiques connu du récepteur et peu se restreindre à l'activation sélective d’un sous-groupe de voies de signalisation.Ce nouveau modèle pharmacologique de l'activation des RCPG ouvre de nouvelles possibilités pour la découverte de médicaments plus efficace et sûr, ciblant les RCPGs. En effet, il permet la conception de molécules modulant spécifiquement les voies signalétiques d’intérêt thérapeutique, sans engager les autres voies qui pourraient mener à des effets secondaires indésirables ou de la tolérance. Cette thèse décrit l'utilisation d'une nouvelle approche sans marquage...

Acoustic Impedance Measurements - Correction for Probe Geometry Mismatch

Fletcher, Neville; Smith, John Robert; Tarnopolsky, Alex Z; Wolfe, Joe
Fonte: Acoustical Society of America Publicador: Acoustical Society of America
Tipo: Artigo de Revista Científica
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The effect of evanescent mode generation, due to geometrical mismatch, in acoustic impedance measurements is investigated. The particular geometry considered is that of a impedance probe with an annular flow port and a central microphone, but the techniques are applicable to other geometries. It is found that the imaginary part of the measured impedance error is proportional to frequency, and that the sign of the error is positive for measurements made on tubes with diameter much larger than that of the inlet port, but negative for tubes with diameter close to that of the inlet. The result is a distortion of the measured frequencies of the impedance minima of the duct while the maxima are largely unaffected. There is, in addition, a real resistive component to the error that varies approximately as the square root of the frequency. Experiment confirms the results of the analysis and calculations, and a calibration procedure is proposed that allows impedance probes that have been calibrated on a semi-infinite tube of one diameter to be employed for measurements on components with an inlet duct of some very different diameter.