Electrical Impedance Tomography

Los procedimientos generalmente utilizados en el laboratorio de función pulmonar informan del comporta-miento global del sistema respiratorio. No obstante, en determinadas circunstancias, como la resección quirúrgica (lobectomía o neumonectomía), antes de tomar decisiones es importante conocer la participación de cada pulmón en la función global 1 . Para valorar lo que se denomina "función pulmonar unilateral" (FPU) se han desarrollado diversos procedimientos: oclusión temporal de la arteria pulmonar 2 , broncoespirometría 3 , pruebas de decúbitos laterales alternativos 4 , gammagrafía de ventilación y perfusión con radioisótopos 5,6 , tomografía com-OBJETIVO: Comparar la función pulmonar unilateral (FPU) estimada mediante tomografía por impedancia eléctrica (TIE) con la misma determinación obtenida a partir de la gammagrafía de ventilación y perfusión pulmonar PACIENTES Y MÉTODOS: Se trata de un estudio clínico prospectivo, realizado en un laboratorio de función pulmonar de un hospital general. Se incluyó a 20 pacientes diagnosticados de cáncer de pulmón (17 varones y 3 mujeres, con edades comprendidas entre los 25 y los 77 años), candidatos a cirugía resectiva pulmonar, a quienes se realizó un estudio de ventilación/perfusión pulmonar con radioisótopos.

Aqueous phase exfoliation was developed for producing high-yield graphene nanosheets from expanded graphite (EG). The process included ultrasonication with sodium dodecyl sulfate (SDS) emulsion in aqueous phase. The high throughput exfoliation process was characterized by UV-vis spectroscopy, transmission electron microscopy (TEM) and electrical impedance spectroscopy (EIS). Controlled sonication experiments revealed that optimum exfoliation corresponds to maxima in UV-vis spectra. TEM results showed that the exfoliated graphene comprised nanoflakes having 65 layers ($60%) and 610 layers for 90% of the product. The potential use of this highly dispersed graphene was demonstrated by onepot synthesis of graphene/polymer composite via in situ emulsion polymerization with styrene. The integrated role of SDS included adsorption and exfoliation of graphite, dispersion of graphene produced and assisting with micelle formation in emulsion. The high surface area graphene nanosheets as dispersed phase in polymeric nanocomposites showed significant improvement in thermal stability and electrical conductivity.

Although electrical impedance tomography (EIT) for ventilation monitoring is on the verge of clinical trials, pulmonary perfusion imaging with EIT remains a challenge, especially in spontaneously breathing subjects. In anticipation of more research on this subject, we believe a thorough review is called for. In this paper, findings related to the physiological origins and electrical characteristics of this signal are

In order to meet the future emissions regulations, nitrogen oxides (NO x ) sensors with a high sensitivity in the low ppm detection range will be required. An integrating NO x sensor concept is proposed for that purpose. In this concept, well-known lean NO x trap (LNT) materials applied on an interdigitated electrode structure are used to accumulate the very low NO x -concentrations downstream of the NO x aftertreatment systems. When operated at 350 • C, the impedance decreased with increased NO storage. We demonstrate that the electrical impedance of such a sensor is a good measure for the amount of stored NO (verifying the integrating properties of the sensor device and its ability to detect very low amounts of NO). Moreover, first sensor tests concerning the cross sensitivity to oxygen and carbon dioxide were conducted. The data presented show that there is no significant influence of the concentration of oxygen and carbon dioxide in a wide range, but it is essential that oxygen is present at all.

Electrical impedance spectroscopy is a minimally invasive technique that has clear advantages for living tissue characterisation owing to its low cost and ease of use. The present paper describes how this technique can be applied to breast tissue classification and breast cancer detection. Statistical analysis is used to derive a set of rules based on features extracted from the graphical representation of electrical impedance spectra. These rules are used hierarchically to discriminate several classes of breast tissue. Results of statistical classification obtained from a data set of 106 cases representing six classes of excised breast tissue show an overall classification efficiency of ~92% with carcinoma discrimination > 86%.

The detection of buried land mines in soil is a well-studied problem; many existing technologies are designed and optimized for performance in different soil types. Research on mine detection in shallow water environments such as beaches, however, is much less developed. Electrical impedance tomography (EIT) shows promise for this application. EIT uses current-stimulating and voltage-recording electrode pairs to measure trans-impedances in the volume directly beneath the electrode array, which sits flat over the ground surface. The trans-impedances are used to construct a conductivity profile of the volume. Non-metallic and metallic explosives appear as perturbations in the conductivity profile, and their location and size can be estimated. Lab testing has yielded promising results using a submerged array positioned over a sand bed. The instrument has also successfully detected surrogate mines in a traditional soil environment during field trials. Resolution of the detector is roughly half the pitch of electrodes in the array. In underwater lab testing, non-conducting targets buried in the sand are detected at a depth of 1.5 times the electrode pitch with the array positioned up to one electrode pitch above the sand bed. Results will be presented for metallic and non-metallic targets of various shapes and sizes.

Finite element analysis has been used to model the ultrasonic wave propagation both in a custom made transducer and in the tested polymer sample. The model consists of acoustic (passive elements) and electroacoustic (active elements) transmission lines. The simulation of the acoustic propagation accounts for the interaction between the transducer and the materials in the buffer rods, and the coupling between the electric and mechanical properties of the piezoelectric material.

We call piezoelectromechanical (PEM) truss beam a truss modular beam coupled with a transmission electrical line when the coupling is obtained by piezoelectric actuators which act as bars in the module and as capacitances in the electrical line.

Electrical impedance spectroscopy is a minimally invasive technique that has clear advantages for living tissue characterisation owing to its low cost and ease of use. The present paper describes how this technique can be applied to breast tissue classification and breast cancer detection. Statistical analysis is used to derive a set of rules based on features extracted from the graphical representation of electrical impedance spectra. These rules are used hierarchically to discriminate several classes of breast tissue. Results of statistical classification obtained from a data set of 106 cases representing six classes of excised breast tissue show an overall classification efficiency of ~92% with carcinoma discrimination > 86%.

A new mathematical model for the bulk electrical impedance of human skin is presented. In particular this model describes the impedance of skin during surface functional neuromuscular stimulation (FNS) with square stimulation pulses. Experimental data are presented that illustrate the nonlinear dynamic properties of human skin during current and voltage controlled stimulation. Model predictions are compared to experimental data, measured under both constant voltage and constant current transcutaneous stimulation. It is found that this model captures a variety of nonlinear time-varying effects observed in the skin impedance when stimulating with either protocol. This model may be used as part of large neuromusculoskeletal models or in the more accurate modeling of transcutaneous FNS, which is currently the most common clinical implementation of FNS.

One of the main causes of damages for wind-turbine power plants is lightning. Direct and indirect events, indeed, can produce damages and malfunctions of electrical and mechanical components. Concerning mechanical components, blades and bearings are the most involved parts. In particular, lightning damages to main-shaft bearings can result in high costs of maintenance, due to the inherent burden in the replacement of these components. The paper focuses on the modeling of wind-turbine main-shaft bearings. Two models are presented and experimentally validated: one numerical and one analytical, both conceived in a way to make the calculation of the bearing electrical impedance possible. The paper shows how these models are helpful for the design of wind-turbines lightning protection systems (LPSs). In this respect, it illustrates the criteria for the design of such an LPS and assesses the validity of design solutions by means of experimental tests.

... [Buy Via Ask*IEEE]; A. Ramirez, W. Daily, D. LaBrecque, E. Owen, and D. Chesnut, "Monitoring an underground steam injection process using electrical resistance tomography", Water Resources Res., vol. 29, pp. 73 - 87, 1993. [CrossRef] [Buy Via Ask*IEEE]; A. Ramirez, W. Daily ...

Abstract-An improved electrical impedance tomographic recon-struction algorithm is presented that is generally guaranteed to con-verge. The algorithm is attractive for several reasons. A modified New-ton-Raphson method varies a finite-element model of resistivities to fit a set of ...

This paper reports the design, development and implementation of a low cost electrical impedance tomography system. A 16 electrode EIT system was designed around a phantom tank. A 60 kHz constant sinusoidal current of up to 1 mA is induced in the first and second electrode and the root-mean-square potential on all the adjacent pairs of electrodes placed clockwise is measured directly by the analogue pins of an Arduino Mega microcontroller. This data is fed and then executed in MATLAB which is interfaced with EIDORS software to reconstruct the image based on the acquired data. This is the most economical EIT system designed and tested so far as compared to other EIT systems.

In this paper, a new approach to obtain sensorless velocity feedback for loudspeakers is developed. The back electromotive force (back-EMF) of the moving coil is estimated by using a disturbance-observer-type estimator based on the coil current measurement. The cone velocity of a loudspeaker can be obtained based on its proportionality to the back-EMF. Instead of relying on the coupled mechanical dynamics as reported in previous work, the proposed velocity estimation is based on the precise knowledge of electrical impedance, which makes it more robust to changes in acoustic loading. The proposed approach enables the development of a robust velocity controller for a subwoofer without an expensive velocity measuring device. Experimental results demonstrated that closed-loop velocity control using the proposed scheme of velocity estimation achieved a performance comparable to that obtained by using measured velocity feedback. The proposed approach can be easily adapted to other moving-coil-type linear actuators.

Ante la posibilidad de realizar un proyecto de investigación se planteó conocer el EIT (método de construcción de imágenes no invasivo e inocuo que permite obtener una sección transversal plana de una estructura tridimensional). El equipo de EIT se puede dividir en dos partes: hardware de adquisición de datos y software encargado de control, procesamiento de señales y reconstrucción de imágenes. La técnica posee una dificultad importante a la hora de la reconstrucción. El objetivo del presente trabajo es brindar una noción amplia de la técnica de EIT realizando una breve revisión: los métodos de estimulación y adquisición de datos, las técnicas de reconstrucción y las aplicaciones clínicas; haciendo foco en la descripción de los métodos de estimulación y medición, describiendo cada uno detalladamente ya que se considera un hito donde se podría potenciar el desarrollo del hardware utilizado para la EIT –y así salvaguardar la dificultad actual-.

Recibido el 24 de junio de 2009; aceptado el 21 de octubre de 2009 Disponible en Internet el 25 de enero de 2010 PALABRAS CLAVE Síndrome de distrés respiratorio agudo; Ventilación mecánica; Tomografía axial computarizada; Lesión asociada a ventilador; Colapso alveolar

Electrical impedance tomography (EIT) is a medical imaging modality that is used to compute the conductivity distribution through measurements on the cross-section of a body part. An elliptic geometry model, which defines a more general frame, ensures more accurate results in reconstruction and assessment of inhomogeneities inside. This study provides a link between the analytical solutions defined in circular and elliptical geometries on the basis of the computation of conformal mapping. The results defined as voltage distributions for the homogeneous case in elliptic and circular geometries have been compared with those obtained by the use of conformal transformation between elliptical and well-known circular geometry. The study also includes the results of the finite element method (FEM) as another approach for more complex geometries for the comparison of performance in other complex scenarios for eccentric inhomogeneities. The study emphasizes that for the elliptic case the analytical solution with conformal transformation is a reliable and useful tool for developing insight into more complex forms including eccentric inhomogeneities.

The kinetics of iron electrodeposition from acid sulphate solutions onto a platinum electrode was investigated by means of stationary polarisation curves and electrochemical impedance spectroscopy. Together with interfacial pH data previously obtained, the effect of pH was analysed. The formation of at least three adsorbed intermediates at the cathode surface was evidenced in all pH values. The relative rate of their formation and its surface concentration depend on the solution pH as well as on the electrode potential. It is suggested that two of these species catalyses the H + reduction whereas the other one may have a blocking effect on this reaction.

The electrical impedance diagnostic methods and instrumentation developed at the Gda ´ nsk and Warsaw Universities of Technology are described. On the basis of knowledge of their features, several original approaches to the broad field of electrical impedance applications are discussed. Analysis of electrical field distribution after external excitation, including electrode impedance, is of primary importance for measurement accuracy and determining the properties of the structures tested. Firstly, the problem of electrical tissue properties is discussed. Particular cells are specified for in vitro and in vivo measurements and for impedance spectrometry. Of especial importance are the findings concerning the electrical properties of breast cancer, muscle anisotropy and the properties of heart tissue and flowing blood. The applications are both important and wide-ranging but, for the present, special attention has been focused on the evaluation of cardiosurgical interventions. Second...

A major factor associated with recent improvements in the clinical performance of cochlear implant patients has been the development of speech-processing strategies based on high stimulation rates. While these processing strategies show clear clinical advantage, we know little of their long-term safety implications. The present study was designed to evaluate the physiological and histopathological effects of long-term intracochlear electrical stimulation using these high rates. Thirteen normal-hearing adult cats were bilaterally implanted with scala tympani electrode arrays and unilaterally stimulated for periods of up to 2100 h using either two pairs of bipolar or three monopolar stimulating electrodes. Stimuli consisted of short duration (25-50 JlS/phase) charge-balanced biphasic current pulses presented at 1000 pulses per second (pps) per channel for monopolar stimulation, and 2000 pps/channel for bipolar stimulation. The electrodes were shorted between current pulses to minimize any residual direct current, and the pulse trains were presented using a 50% duty cycle (500 ms on; 500 ms off) in order to simulate speech. Both acoustic (ABR) and electrical (EABR) auditory brainstem responses were recorded periodically during the chronic stimulation program. All cochleas showed an increase in the click-evoked ABR threshold following implant surgery; however, recovery to near-normal levels occurred in approximately half of the stimulated cochleas 1 month post-operatively. The use of frequency-specific stimuli indicated that the most extensive hearing loss generally occurred in the high-frequency basal region of the cochlea (12 and 24 kHz) adjacent to the stimulating electrode. However, thresholds at lower frequencies (2, 4 and 8 kHz), appeared at near-normal levels despite long-term electrode implantation and electrical stimulation. Our longitudinal EABR results showed a statistically significant increase in threshold in nearly 40% of the chronically stimulated electrodes evaluated; however, the gradient of the EABR input/output (I/0) function (evoked potential response amplitude versus stimulus current) generally remained quite stable throughout the chronic stimulation period. Histopathological examination of the cochleas showed no statistically significant difference in ganglion cell densities between cochleas using monopolar and bipolar electrode configurations (P = 0.67), and no evidence of cochlear damage caused by high-rate electrical stimulation when compared with control cochleas. Indeed, there was no statistically significant relationship between spiral ganglion cell density and electrical stimulation (P = 0.459), or between the extent of loss of inner (IHC, P = 0.86) or outer (OHC, P = 0.30) hair cells and electrical stimulation. Spiral ganglion cell loss was, however, influenced by the degree of inflammation (P=O.Ol6) and electrode insertion trauma. These histopathological findings were consistent with the physiological data. Finally, electrode impedance, measured at completion of the chronic stimulation program, showed close correlation with the degree of tissue response adjacent to the electrode array. These results indicated that chronic intracochlear electrical stimulation, using carefully controlled charge-balanced biphasic current pulses at stimulus rates of up to 2000 pps/channel, does not appear to adversely affect residual auditory nerve elements or the cochlea in general. This study provides an important basis for the safe application of improved speech-processing strategies based on high-rate electrical stimulation.

In electrical impedance tomography (EIT), current patterns are injected into a subject and boundary voltages are measured to reconstruct a cross-sectional image of resistivity distribution. Static EIT image reconstruction requires a computer model of a subject, an efficient data-collection method and robust and fast reconstruction algorithms. The finite-element method is used as the computer model. The paper describes the finite-element analysis software package developed, including an interactive graphical mesh generator and fast algorithms for solving linear systems of equations using sparse-matrix and vector techniques. Various models of irregularly shaped subjects are developed using mesh-design tools, including automatic mesh generation and optimisation using the Delaunay algorithm. Even though the software package is customised for use in electrical impedance tomography, it can be used for other biomedical research areas, such as impedance cardiography, cardiac defibrillation and impedance pneumography.

Electrical impedance tomography measurements in clinical applications are limited by an undesired noise component. We have investigated the noise in three systems suitable for imaging epileptic seizures, the UCH Mark1b, UCH Mark2.5 and KHU Mark1 16 channel, at applied frequencies in three steps from 1 to 100 kHz, by varying load impedance, single terminal or multiplexed measurements, and in test objects of increasing complexity from a resistor to a saline filled tank and human volunteer. The noise was white, and increased from about 0.03% rms on the resistor to 0.08% on the human; it increased with load but was independent of use of the multiplexer. The KHU Mark1 delivered the best performance with noise spectra of about 0.02%, which could be further reduced by averaging to a level where reliable imaging of changes of about 0.1% estimated during epileptic seizures appears plausible.

Breathing moves volumes of electrically insulating air into and out of the lungs, producing conductivity changes which can be seen by electrical impedance tomography (EIT). It has thus been apparent, since the early days of EIT research, that imaging of ventilation could become a key clinical application of EIT. In this paper, we review the current state and future prospects for lung EIT, by a synthesis of the presentations of the authors at the 'special lung sessions' of the annual biomedical EIT conferences in 2009-2011. We argue that lung EIT research has arrived at an important transition. It is now clear that valid and reproducible physiological information is available from EIT lung images. We must now ask the question: How can these data be used to help improve patient outcomes? To answer this question, we develop a classification of possible clinical scenarios in which EIT could play an important role, and we identify clinical and experimental research programmes and engineering developments required to turn EIT into a clinically useful tool for lung monitoring.

Simultaneous in situ UV-Vis-NIR spectro-electrochemical and a.c. impedance techniques have been realized for the first time. Combination of the data obtained by these parallel, independent methods can be exploited in the future in the elucidation of the redox mechanism of various transparent electroactive layers.

The objective of this paper is to study mixing of two miscible liquids in turbulent flow. Strictly speaking we are studying the performance and mixing patterns of TrumpJet ® mixing system of papermaking chemicals and additives. TrumpJet ® is a jet injection mixer developed and produced by Wetend Technologies Ltd. The studies are made in cooperation with the company. As a monitoring system, we use an electrical impedance tomography system developed at the Department of Physics, University of Kuopio. In this study only eight current injections are used and 64 corresponding voltages are measured. The frame rate of the system is about 40 frames/s. Difference reconstruction approach is used to produce three-dimensional images of the conductivity distribution. In order to quantify the quality of mixing, mixing index is calculated based on the reconstructed images. Laboratory tests are done in pilot plant. We compare the mixing of chemical to the main flow with TrumpJet technology to conventional chemical injection system.

Barium strontium gadolinium bismuth niobate (Ba0.1Sr0.81Gd0.06Bi2Nb2O9, BSGBN) ceramics were prepared by using the conventional solid-state reaction method. The dielectric permittivity, modulus and impedance spectroscopy studies on BSGBN were investigated in the frequency range, 45 Hz–5 MHz and in the temperature range from room temperature (RT) to 570 °C. The dielectric anomaly with a broad peak was observed at 470 °C. Simultaneous substitution of Ba2+ and Gd3+ increases the transition temperature of SrBi2Nb2O9 (SBN) from 392 to 470 °C. XRD studies in BSGBN revealed an orthorhombic structure with lattice parameters a = 5.4959 Å, b/a = 1.000, c = 25.0954 Å. Impedance and modulus plots were used as tools to analyse the sample behaviour as a function of frequency. Cole-Cole plots showed a non-Debye relaxation. Also, dc and ac conductivity measurements were performed on BSGBN. The electric impedance which describes the dielectric relaxation behaviour is fitted to the Kohlrausch exponential function. Near the phase transition temperature, a stretched exponential parameter β indicating the degree of distribution of the relaxation time has a small value.

In this paper, we analyze the vibrational spectra of mechanical resonators actuated piezoelectrically with aluminum nitride (AlN) films. The microresonators consist in bimorph cantilevers with different lengths containing a piezoelectric metal/AlN/metal stack supported by a silicon nitride structural layer. The thicknesses of both the AlN and Si 3 N 4 layers are varied between 0.3 µm and 1 µm to study their influence on the mechanical response of the cantilevers. The motion of the cantilevers electrically driven is first assessed by optical laser interferometry; resonant frequencies varying between 100 kHz and 8 MHz are obtained. Additionally, many of the vibrational modes are detected by measuring the changes of the electrical impedance at the resonant frequencies. The mass detection factor of the cantilevers is assessed by measuring the frequency shift after mass loading with thin SiO 2 layers. A value of 0.18 fg/Hz is obtained for vibrational modes around MHz.

An impedentiometric electronic tongue based on the combination of a composite sensor array and chemometric techniques aimed at the discrimination of soluble compounds able to elicit different gustative perceptions is presented. A composite array consisting of chemo-sensitive layers based on carbon nanotubes or carbon black dispersed in polymeric matrices and doped polythiophenes was used. The electrical impedance of the sensor array was measured at a frequency of 150 Hz by means of an impedance meter. The experimental set-up was designed in order to allow the automatic selection of a test solution and dipping of the sensor array following a dedicated measurement protocol. Measurements were carried out on 15 different solutions eliciting 5 different tastes (sodium chloride, citric acid, glucose, glutamic acid and sodium dehydrocholate for salty, sour, sweet, umami and bitter, respectively) at 3 concentration levels comprising the human perceptive range. In order to avoid over-fitting, more than 100 repetitions for each sample were carried in a 4-month period. Principal component analysis (PCA) was used to detect and remove outliers. Classification was performed by linear discriminant analysis (LDA). A fairly good degree of discrimination was obtained.

Several papers on induced current electrical impedance tomography (IC-EIT) have dwelt on potential advantages of this technique over conventional EIT which uses applied current (AC-EIT). Experimental evidence that IC-EIT could surpass AC-EIT in similar imaging conditions is lacking. In this paper, we describe a system that can switch rapidly between both AC-EIT and IC-EIT. The system makes it possible to image objects in a saline-filled tank, providing data acquired in identical test conditions for comparing the performance of the two modes. The system uses eight circular coils and 16 electrodes to acquire 120 linearly independent measurements in IC-EIT and 104 in AC-EIT. Difference images were reconstructed from data acquired with both modes using the maximum a posteriori method. Spatial resolution was lower in IC-EIT images than in AC-EIT, especially in the radial direction. IC-EIT also exhibits a bias toward the center for positioning a conductivity perturbation. These results were obtained for a typical coil configuration widely used in the literature and may not be representative of alternate coil configurations. The system described in this paper provides stable experimental conditions for comparing the performance of the two EIT imaging modes and would be a valuable tool for validating new coil configurations.

Detection of local lung air content by electrical impedance tomography compared with electron beam CT. The aim of the study was to validate the ability of electrical impedance tomography (EIT) to detect local changes in air content, resulting from modified ventilator settings, by comparing EIT findings with electron beam computed tomography (EBCT) scans obtained under identical steady-state conditions. The experiments were carried out on six anesthetized supine pigs ventilated with five tidal volumes (VT) at three positive end-expiratory pressure (PEEP) levels. The lung air content changes were determined both by EIT (Goe-MF1 system) and EBCT (Imatron C-150XP scanner) in six regions of interest, located in the ventral, middle, and dorsal areas of each lung, with respect to the reference air content at the lowest VT and PEEP, as a change in either local electrical impedance or lung tissue density. An increase in local air content with VT and PEEP was identified by both methods at all regions studied. A good correlation between the changes in lung air content determined by EIT and EBCT was revealed. Mean correlation coefficients in the ventral, middle, and dorsal regions were 0.81, 0.87, and 0.93, respectively. The study confirms that EIT is a suitable, noninvasive method for detecting regional changes in air content and monitoring local effects of artificial ventilation.

Hybrid imaging techniques utilize couplings of physical modalities -they are called hybrid, because, typically, the excitation and measurement quantities belong to different modalities. Recently there has been an enormous research interest in this area because these methods promise very high resolution. In this paper we give a review on hybrid tomography methods for electrical conductivity imaging. The reviewed imaging methods utilize couplings between electric, magnetic and ultrasound modalities. By this it is possible to perform high-resolution electrical impedance imaging and to overcome the low-resolution problem of electric impedance tomography.

It has been known for some time that many tumors have a significantly different conductivity and permittivity from surrounding normal tissue. This high ldquocontrastrdquo in tissue electrical properties, occurring between a few kilohertz and several megahertz, may permit differentiating malignant from benign tissues. Here we show the ability of electrical impedance spectroscopy (EIS) to roughly localize and clearly distinguish cancers from normal tissues and benign lesions. Localization of these lesions is confirmed by simultaneous, in register digital breast tomosynthesis (DBT) mammography or 3-D mammograms.

Thoracic electrical impedance tomography (EIT) is a noninvasive, radiation-free monitoring technique whose aim is to reconstruct a cross-sectional image of the internal spatial distribution of conductivity from electrical measurements made by injecting small alternating currents via an electrode array placed on the surface of the thorax. The purpose of this paper is to discuss the fundamentals of EIT and demonstrate the principles of mechanical ventilation, lung recruitment, and EIT imaging on a comprehensive physiological model, which combines a model of respiratory mechanics, a model of the human lung absolute resistivity as a function of air content, and a 2-D finite-element mesh of the thorax to simulate EIT image reconstruction during mechanical ventilation. The overall model gives a good understanding of respiratory physiology and EIT monitoring techniques in mechanically ventilated patients. The model proposed here was able to reproduce consistent images of ventilation distribution in simulated acutely injured and collapsed lung conditions. A new advisory system architecture integrating a previously developed data-driven physiological model for continuous and noninvasive predictions of blood gas parameters with the regional lung function data/information generated from absolute EIT (aEIT) is proposed for monitoring and ventilator therapy management of critical care patients.

A bipolar membrane (BM) is composed of one cation and one anion ion-exchange layers joined together in series. In order to obtain the AC electrical impedance of a BM, a small sinusoidal current perturbation was superimposed to the DC current, and the resulting frequency-dependent impedance spectra were recorded under different conditions of electrical polarisation and temperature for ®ve BMs. The experimental spectra were measured in three current ranges: below the limiting current region, at the onset of the overlimiting region and in the electric ®eld enhanced water dissociation region. This allows for a better understanding of the contributions of the salt and water ions to the measured impedance spectra. Measurements of the impedance of the forward biased membrane were also carried out. Although the experimental impedance spectra appear to be in qualitative agreement with previous theoretical models incorporating the effect of the electric ®eld enhanced water dissociation, a quantitative analysis of the results is not still possible due to the high number of parameters involved. # 1998 Elsevier Science B.V. All rights reserved.