Time-scaling based sliding mode control for Neuromuscular Electrical Stimulation under uncertain relative degrees.

This paper addresses the application of the sliding mode approach to control the arm movements by artificial recruitment of muscles using Neuromuscular Electrical Stimulation (NMES). Such a technique allows the activation of motor nerves using surface electrodes. The goal of the proposed control system is to move the upper limbs of subjects through electrical stimulation to achieve a desired elbow angular displacement. Since the human neuro-motor system has individual characteristics, being time-varying, nonlinear and subject to uncertainties, the use of advanced robust control schemes may represent a better solution than classical Proportional-Integral (PI) controllers and model-based approaches, being simpler than more sophisticated strategies using fuzzy logic or neural networks usually applied in this control problem. The objective is the introduction of a new time-scaling base sliding mode control (SMC) strategy for NMES and its experimental evaluation. The main qualitative advantages of the proposed controller via time-scaling procedure are its independence of the knowledge of the plant relative degree and the design/tuning simplicity. The developed sliding mode strategy allows for chattering alleviation due to the impact of the integrator in smoothing the control signal. In addition, no differentiator is applied to construct the sliding surface. The stability analysis of the closed-loop system is also carried out by using singular perturbation methods. Experimental results are conducted with healthy volunteers as well as stroke patients. Quantitative results show a reduction of 45% in terms of root mean square (RMS) error (from 5.9° to [Formula: see text] ) in comparison with PI control scheme, which is similar to that obtained in the literature.

Assessment of tooth structure using an alternative electrical bioimpedance spectroscopy method.

In the past few years bioimpedance has been used in many applications in dentistry, such as estimating the length of root canals and the physical properties of enamel. Despite the significant number of studies using bioimpedance to investigate the dental structure, many of them use only the real component of bioimpedance, i.e., the resistance, disregarding the information provided by the imaginary one, i.e., the reactance. Moreover, in different studies that investigate both parts of bioimpedance, the data are obtained by using single frequency or multifrequency methods based on sinusoidal sweep. The aim of this study was to investigate the use of an alternative bioimpedance spectroscopy (BIS) method based on step response in the assessment of tooth structure. To test the feasibility of the studied method we performed in vitro experiments that considered the successive removal of enamel layers of 22 healthy teeth, the accomplishment of the BIS method, and the estimate of bioimpedance parameter that were associated with the changes in the tooth structure. To deal with the variability of bioimpedance parameters a dental health index (DHI) is proposed. The findings include the behavior of bioimpedance parameters of intact teeth, as well as those associated with the successive removal of the enamel layer, and indicate that DHI is sensitive enough to detect changes of the enamel layer. The results point to the feasibility of the studied BIS method in evaluating tooth structure and that it might be used to assess dental health.

Assessment of Tooth Structure using an Alternative Electrical Bioimpedance Spectroscopy Method

In the past few years bioimpedance has been used in many applications in dentistry, such as estimating the length of root canals and the physical properties of enamel. Despite the significant number of studies using bioimpedance to investigate the dental structure, many of them use only the real component of bioimpedance, i.e., the resistance, disregarding the information provided by the imaginary one, i.e., the reactance. Moreover, in different studies that investigate both parts of bioimpedance, the data are obtained by using single frequency or multifrequency methods based on sinusoidal sweep. The aim of this study was to investigate the use of an alternative bioimpedance spectroscopy (BIS) method based on step response in the assessment of tooth structure. To test the feasibility of the studied method we performed in vitro experiments that considered the successive removal of enamel layers of 22 healthy teeth, the accomplishment of the BIS method, and the estimate of bioimpedance parameter that were associated with the changes in the tooth structure. To deal with the variability of bioimpedance parameters a dental health index (DHI) is proposed. The findings include the behavior of bioimpedance parameters of intact teeth, as well as those associated with the successive removal of the enamel layer, and indicate that DHI is sensitive enough to detect changes of the enamel layer. The results point to the feasibility of the studied BIS method in evaluating tooth structure and that it might be used to assess dental health.

Nos últimos anos a bioimpedância tem sido usada em aplicações odontológicas tais como estimativas de profundidade do canal radicular e na investigação de propriedades do esmalte. Apesar do número significativo de estudos usando a técnica de bioimpedância para avaliar a estrutura dental, muitos trabalhos usam somente a componente real da bioimpedância, isto é, a resistência; desprezando a informação fornecida pela parte imaginária, isto é, a reatância. Além disso, em diversos trabalhos que investigam ambas as partes da bioimpedância, os dados são, geralmente, obtidos por métodos monofrequenciais ou multifrequenciais baseados na varredura senoidal. O objetivo deste estudo foi investigar o uso de um método alternativo de espectroscopia de bioimpedância (BIS) baseado na resposta de corrente a um degrau de tensão na avaliação da estrutura do dente. Para testar a viabilidade do método alternativo realizamos experimentos in vitro que consideraram a remoção da camada de esmalte de 22 dentes hígidos, a aplicação do método BIS e a estimativa de parâmetros de bioimpedância que foram associados às mudanças na estrutura do dente. Para enfrentar o problema da variabilidade dos parâmetros de bioimpedância um índice de saúde dental (DHI) é proposto. Os resultados incluem o comportamento dos parâmetros de bioimpedância de dentes hígidos, assim como aqueles associados às sucessivas remoções da camada de esmalte; indicando que o DHI é sensível para detectar mudanças na camada de esmalte. Os achados apontam para a viabilidade do método de BIS estudado na avaliação da estrutura do dente e que ele poderia ser usado para quantificação da saúde dental.

Algoritmo de reconstrução de imagens para um sistema de Tomografia por Impedância Elétrica (TIE) baseado em configuração multiterminais / Image reconstruction algorithm for a multiterminal-based Electrical Impedance Tomography (EIT) system

INTRODUÇÃO: A Tomografia por Impedância Elétrica (TIE) é um método de imageamento de baixo custo, não invasivo, portátil e livre de radiacão ionizante, que é capaz de mapear a distribuicão das propriedades elétricas de tecidos biológicos. Apesar da baixa resolucão das imagens reconstruídas, quando comparadas a outras técnicas de imageamento tomográfico, tem-se observado uma série de aplicacões clínicas nas quais a EIT é utilizada para monitorar a atividade de determinados tecidos do corpo humano. A maioria dos sistemas de EIT comerciais tem sido pautada no paradigma originalmente proposto de uma configuracão multiportas. Este trabalho apresenta um algoritmo de reconstrucão de imagem para um sistema alternativo de EIT que usa uma configuracão multiterminais. MÉTODOS: O algoritmo é baseado na associacão entre o plano tomográfico do volume condutor e um sistema eletrostático análogo. Para avaliar o algoritmo, imagens de EIT foram reconstruídas a partir de dados obtidos experimentalmente em tanque com solucão salina, sendo as mesmas quantificadas por meio de métricas estabelecidas para este propósito. RESULTADOS: Quantitativamente, as imagens reconstruídas com o algoritmo proposto apresentaram um erro de posicão de ±10%, resolucão e deformacão decrescentes do centro para a borda e oscilacão em torno de 60% do meio. CONCLUSÃO: Uma vez que o algoritmo não possui nenhum processo de filtragem, os resultados foram considerados satisfatórios e encorajadores para trabalhos futuros visando melhorias.

INTRODUCTION: Electrical Impedance Tomography (EIT) is a low cost, non-invasive, portable and free of ionizing radiation method for imaging the distribution of the electric properties of biological tissues. Despite the low resolution of the reconstructed images when compared with other tomographic techniques, there is a range of clinical applications in which the EIT has been used to monitor the activity of certain body tissues. Most of commercial EIT systems are based on the original paradigm defined as a multiport configuration. This paper presents an algorithm developed to reconstruct images for an alternative multiterminal-based EIT system. METHODS: The algorithm is based on the association between the tomographic plane of the conductor volume and an analogous electrostatic system. To evaluate the algorithm, EIT images were reconstructed using data obtained experimentally in a saline solution tank, which were quantified by some metrics established for this purpose. RESULTS: Quantitatively, EIT images reconstructed by the proposed algorithm presented a position error around ±10%, resolution and shape deformation decreasing from center to the edge, and ringing around 60% of the medium. CONCLUSION: Taking into account that no filtering was used in the algorithm, the results can be considered satisfactory and encourage future works aiming further improvement.

Influência de parâmetros da estimulação elétrica funcional na contração concêntrica do quadríceps / Influence of functional electrical stimulation parameters in quadriceps concentric contraction

INTRODUÇÃO: Sistemas de estimulacão elétrica funcional (FES) são usados na pràtica clínica para o fortalecimento muscular, assim como para a recuperacão e preservacão funcional dos músculos enfraquecidos. Porém, uma das dificuldades encontradas na sua aplicacão é a falta de padrões adequados para a realizacão de um movimento pré-estabelecido, uma vez que os parâmetros da estimulacão (frequência, intensidade de corrente e duracão do pulso) são variados heuristicamente. O presente trabalho investigou a influência dos paraêmetros da FES usada no estabelecimento da posicão angular e forca produzida na extensão de joelho. MÉTODOS: O procedimento experimental foi dividido em duas fases chamadas Fase I e Fase II. A amostra total do estudo foi composta por 41 voluntàrios saudàveis de ambos os sexos (27 na Fase I e 14 na Fase II). Durante a Fase I cada voluntàrio foi estimulado com 18 combinacões diferentes de parâmetros para a FES, com o objetivo de determinar um modelo capaz de prever o movimento realizado para cada padrão de estimulacão. RESULTADOS: As diferentes duracões de pulso aplicadas não resultaram em alteracões significativas nos movimentos produzidos. Dentre os valores de frequência investigados, 50 Hz foi escolhida para a Fase II, por ter apresentado maior diferenca estatisticamente significativa para os valores de intensidade de corrente avaliados. Durante a Fase II, a intensidade de corrente da FES foi ajustada segundo um modelo linear estabelecido durante a primeira fase e que considerou características antropométricas dos sujeitos; encontrando-se um coeficiente de correlação r = 0,798 entre o ângulo pré-estabelecido e o ângulo alcancado. CONCLUSÃO: Este trabalho apresenta um modelo para a determinação de parâmetros de FES que permitem estabelecer variações angulares da articulação do joelho associadas à eletroestimulação. Considerando a frequência e a duração de pulsos constantes, se estima, usando uma equação de primeira ordem ...

INTRODUCTION: Functional electrical stimulation (FES) is used in clinical practice for muscle strengthening, as well as for functional recovery and preservation of weakened muscles. However, one of the problems in clinical application is the lack of adequate standards for determining the attainment of a predetermined movement, since the stimulation parameters are often adjusted heuristically. The present study investigated the influence of some parameters (frequency, current intensity and pulse duration) of the FES used to establish the joint angle and force produced in knee extension. METHODS: The experimental procedure was divided in two phases (Phase I and Phase II). The total sample included 41 healthy volunteers of both sexes (27 and 14 in Phase I and Phase II). During Phase I 18 profiles of FES were applied in the quadriceps muscle of subjects, changing the above-mentioned FES parameters. RESULTS: It was observed that the pulse duration of the electrical stimulation pulse did not exhibit significant relevance in the evoked movements. Among the discrete values of frequency investigated, the stimulation at 50 Hz was selected because it showed higher statistical significant difference considering the values of current intensity measured. During the Phase II, devoted to place the knee joint angle in a pre-determined value, the current intensity of the FES was adjusted according to the linear model established during the Phase I, which considered anthropometric characteristics of the subjects. In this Phase we found a correlation coefficient r = 0,798 between the pre-determined angle and the reached one. CONCLUSION: This paper presents a model for the determination of FES parameters for establishing angular variations of the knee associated with electrical stimulation. Considering frequency and pulse duration constants we estimate, using a first order equation and correlation coefficient of 0.72, the current intensity dependent of desired angle variation.

Knee bioelectric impedance assessment in healthy/with osteoarthritis subjects.

The present study analyzes parameters estimated by bioelectric impedance spectroscopy (BIS) in subjects with healthy and with osteoarthritis (OA) knees. Thirty-two male volunteers, members of the Parachute Military Infantry Brigade of Rio de Janeiro, Brazil, participated in the study (62 knee joints). Clinical specialists used the Dejour scale for OA classification and divided the subjects into a control (without OA) and a pathological group (with different degrees of OA). BIS data were obtained in a standing position using a BIS technique based on the current response to a step voltage excitation. Differences between groups were measured by means of a Wilcoxon-Mann-Whitney test. Results indicate that raw bioimpedance parameters seem to be sensitive to the physiological changes associated with OA. Thus, data indicate that extra-cellular resistance (Re) and reactance of the equivalent capacitance (Xcx) increase according to the disease intensity (p < 0.001). In conclusion, the BIS technique seems to be able to provide the objective and non-invasive basis for helping the diagnosis of knee OA.

Comparative effects of vaporized perfluorohexane and partial liquid ventilation in oleic acid-induced lung injury.

BACKGROUND: It is currently not known whether vaporized perfluorohexane is superior to partial liquid ventilation (PLV) for therapy of acute lung injury. In this study, the authors compared the effects of both therapies in oleic acid-induced lung injury. METHODS: Lung injury was induced in 30 anesthetized and mechanically ventilated pigs by means of central venous infusion of oleic acid. Animals were assigned to one of the following groups: (1) control or gas ventilation (GV), (2) 2.5% perfluorohexane vapor, (3) 5% perfluorohexane vapor, (4) 10% perfluorohexane vapor, or (5) PLV with perfluorooctane (30 ml/kg). Two hours after randomization, lungs were recruited and positive end-expiratory pressure was adjusted to obtain minimal elastance. Ventilation was continued during 4 additional hours, when animals were killed for lung histologic examination. RESULTS: Gas exchange and elastance were comparable among vaporized perfluorohexane, PLV, and GV before the open lung approach was used and improved in a similar fashion in all groups after positive end-expiratory pressure was adjusted to optimal elastance (P < 0.05). A similar behavior was observed in functional residual capacity (FRC) in animals treated with vaporized perfluorohexane and GV. Lung resistance improved after recruitment (P < 0.05), but values were higher in the 10% perfluorohexane and PLV groups as compared with GV (P < 0.05). Interestingly, positive end-expiratory pressure values required to obtain minimal elastance were lower with 5% perfluorohexane than with PLV and GV (P < 0.05). In addition, diffuse alveolar damage was significantly lower in the 5% and 10% perfluorohexane vapor groups as compared with PLV and GV (P < 0.05). CONCLUSIONS: Although the use of 5% vaporized perfluorohexane permitted the authors to reduce pressures needed to stabilize the lungs and was associated with better histologic findings than were PLV and GV, none of these perfluorocarbon therapies improved gas exchange or lung mechanics as compared with GV.

Effects of filtering and delays on the estimates of a nonlinear respiratory mechanics model.

Estimation of mechanical properties of the respiratory system may be disturbed by instrumentation and physical set-up. The effects of lowpass filtering, filter mismatch and inter-channel delay in the digital converter are assessed on numerically simulated signals from a nonlinear model of the respiratory system. Large biases in model parameter estimates (up to about -300% for some parameters) were caused by these instrumental interferences and were reduced by including an inertance in the retrieved model. The results reinforce the importance of a careful evaluation of the instrumental set-up used in physiological measurements.

Controle automático da ventilação mecânica para minimizar a lesão pulmonar induzida pela ventilação / Automatic control of the mechanical ventilation for minimizing the ventilation induced lung injury

O ajuste de parâmetros dos ventiladores mecânicos pulmonares para evitar a reabertura cíclica de unidades alveolares e pequenas vias aéreas, assim como a hiperdistensão dos septos alveolares, tem sido motivo de atenção nos últimos anos. Este trabalho utiliza um modelo de lesão pulmonar aguda (ALI) em suínos para testar um controlador de ventiladores em malha fechada baseado em regras e modelos discutidos na literatura. Utiliza-se um modelo polinomial da cursa pressão-volume do sistema respiratório para o ajuste da pressão positiva ao final da expiração (PEEP), visando evitar a reabertura cíclica de unidades alveolares, e o ajuste do volume corrente, visando evitar a hiperdistensão pulmonar. Um índice de hiperdistensão baseado na identificação de uma elastância não linear para o sistema respiratório permite o uso do controlador com qualquer forma de onda de ventilação constrolada. Os resultados do controlador proposto foram confrontados com resultados obtidos na ventilação de um grupo controle, manualmente ventilados com base nas mesmas premissas. Como resultado, o controlador automático obteve valores de PEEP dentro da faixa de valores obtidos no grupo controle, porém com menor dispersão. O índice de hiperdistensão calculado ficou abaixo do limiar de hiperdistensão em 5 dos 6 animais do grupo ventilado automaticamente, e em 3 dos 6 animais ventilados do grupo controle. O controlador se comportou de forma estável e os resultados recomendam seu uso em ALI.

Mínimos quadrados aplicados à identificaçäo de parâmetros da mecânica respiratória: identificaçäo de mecânica respiratória pelo método de mínimos quadrados / Mean square applied to identify the mechanics respiratory parameters: identification the respiratory mechanics by Mean square method

A técnica de mínimos quadrados aplicada à identificação da mecânica do sistema respiratório (SR) baseado num modelo unicompartimental simples é discutida neste trabalho. Os resultados mostram que apenas o PEEP (pressão positiva ao fim da expiração) é sempre bem identificado. Em alguns casos, a complacência dinâmica também pode ser bem determinada. O método pode se prestar bem para a monitorização contínua do PEEP e da evolução do quadro clínico.