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Biomedical Engineering, IEEE Transactions on

Issue 4 • Date April 1999

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Displaying Results 1 - 13 of 13
  • Modeling the relationship between concurrent epicardial action potentials and bipolar electrograms

    Page(s): 365 - 376
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    A signal analysis approach to building the relationship between concurrent epicardial cell action potentials (AP's) and bipolar electrograms is presented. Wavelet network, one nonlinear black-box modeling method, is used to identify the relationship between cell AP's and bipolar electrocardiograms. The electrical signals were simultaneously measured from the epicardium of isolated Langendorff-perfused rabbit hearts during three different rhythm conditions: normal sinus rhythm (NSR), normal sinus rhythm after ischemia (NSRI), and ventricular fibrillation (VP). For NSR and NSRI, the proposed modeling method successfully captures the nonlinear input-output relationship and provides an accurate output, but the method fails in case of VF. This result suggests that a time-invariant nonlinear modeling method such as wavelet network is not appropriate for VF rhythm, which is thought to be time-varying as well as chaotic, but still useful in detection of VF. A new arrhythmia detection algorithm, with potential application in implantable devices, is proposed for identifying the time of rhythmic bifurcation. View full abstract»

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  • Is accurate recording of the ECG surface Laplacian feasible?

    Page(s): 377 - 381
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (149 KB)  

    Experimental and model studies were performed to measure the electrocardiographic surface Laplacian using a rectangular finite difference approximation. The experimental approach used ten normal subjects with two sites on the torso. Electrode spacing was 2 cm. The surface Laplacian is theoretically independent of rotation of the electrode array. The data showed considerable variation with rotation. Model studies employed a realistic 23-dipole source. A spherical volume conductor showed invariance with rotation, as anticipated theoretically. A realistic torso, however, showed variation with rotation, although not as severe as that measured. A separate experimental study considered the signal-to-noise ratio (SNR) for the surface Laplacian. The average SNR was 3.3 and 2.5 at the two sites. These results raise serious questions about the practical ability to measure the surface Laplacian on the torso. View full abstract»

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  • A mathematical model of the carotid baroregulation in pulsating conditions

    Page(s): 382 - 392
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    A mathematical model of short-term arterial pressure control by the carotid baroreceptors in vagotomized subjects is presented. It includes an elastance variable description of the left and right heart, the systemic and pulmonary circulations, the afferent carotid baroreceptor pathway, a central elaboration unit, and the action of five effector mechanisms. Simulation results suggest that the carotid baroreflex is able to significantly modulate the cardiac function curve, but this effect is masked in vivo by changes in arterial pressure and atrial pressure. During heart pacing, cardiac output increases with frequency at moderate levels of heart rate, then fails to increase further due to a reduction in stroke volume. Shifting from nonpulsatile to pulsatile perfusion of the carotid sinuses decreases the overall baroreflex gain. Finally, a sensitivity analysis suggests that venous unstressed volume control plays the major role in the early hemodynamic response to acute hemorrhage, whereas systemic resistance control is less important. In all cases, there has been satisfactory agreement between model and experimental results. View full abstract»

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  • Computational fluid dynamic and magnetic resonance analyses of flow distribution between the lungs after total cavopulmonary connection

    Page(s): 393 - 399
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    Total cavopulmonary connection is a surgical procedure adopted to treat complex congenital malformations of the right heart. It consists basically in a connection of both venae cavae directly to the right pulmonary artery. In this paper a three-dimensional model of this connection is presented, which is based on in vivo measurements performed by means of magnetic resonance. The model was developed by means of computational fluid dynamics techniques, namely the finite element method. The aim of this study was to verify the capability of such a model to predict the distribution of the blood flow into the pulmonary arteries, by comparison with in vivo velocity measurements. Different simulations were performed on a single clinical case to test the sensitivity of the model to different boundary conditions, in terms of inlet velocity profiles as well as outlet pressure levels. Results showed that the flow distribution between the lungs is slightly affected by the shape of inlet velocity profiles, whereas it is influenced by different pressure levels to a greater extent. View full abstract»

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  • The effect of artifact rejection by signal-space projection on source localization accuracy in MEG measurements

    Page(s): 400 - 408
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    The consequences of artifact suppression by means of signal-space projection on dipole localization accuracy for magnetoencephalography measurements are studied. Approximate analytical formulas, equivalent to the Cramer-Rao bound, are presented and verified by Monte Carlo simulations which relate the increase of localization error for individual coordinates to the similarity of the artifact field and respective (contravariant) quadrupole fields obtained by differentiating the dipole field with respect to its origin. The expressions simplify significantly for dipoles placed below the center of the measuring system giving rise to highly symmetric field patterns. Formulas are presented both for single- and for multiple-artifact rejection. As illustrative examples artifact fields are constructed which (a) lead to highly decreasing signal-to-noise ratio and goodness-of-fit (GOF), while the localization error is unaffected for all coordinates and (b) lead to an increase of localization error while the SNR and the GOF stays constant. Finally, the rich structure of localization error increase is demonstrated for a class of artifact fields originating from artifact current dipoles. View full abstract»

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  • A robust ensemble data method for identification of human joint mechanical properties during movement

    Page(s): 409 - 419
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    This paper describes a perturbation method for the identification of linear time-varying systems with an unknown input (voluntary joint input) using ensemble data. The method separates the unknown input and the perturbation through high-pass filtering and recasts the multi-input single-output system identification into single-input single-output system identification. The method is robust to intertrial variation, and can track changes of system dynamics up to 5 Hz. Analysis and simulation are given for the conditions similar to those for the human arm experiments. Experiments show that mechanical properties of the human elbow joint change with voluntary movement speed and that the mean stiffness with voluntary movement is in the range of the posture and is higher than reported before. View full abstract»

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  • New thermal wave aspects on burn evaluation of skin subjected to instantaneous heating

    Page(s): 420 - 428
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    Comparative studies on the well-known Pennes' equation and the newly developed thermal wave model of bioheat transfer (TWMBT) were performed to investigate the wave like behaviors of bioheat transfer occurred in thermal injury of biological bodies. The one-dimensional TWMBT in a finite medium was solved using separation of variables and the analytical solution showed distinctive wave behaviors of bioheat transfer in skin subjected to instantaneous heating. The finite difference method was used to simulate and study practical problems involved in burn injuries in which skin was stratified as three layers with various thermal physical properties. Deviations between the TWMBT and the traditional Pennes' equation imply that, for high flux heating with extremely short duration (i.e., flash fire), the TWMBT which accounts for finite thermal wave propagation may provide realistic predictions on burn evaluation. A general heat flux criterion has been established to determine when the thermal wave propagation dominates the principal heat transfer process and the TWMBT can be used for tissue temperature prediction and burn evaluation. A preliminary interpretation on the mechanisms of the wave like behaviors of heat transfer in living tissues was conducted. The application of thermal wave theory can also be possibly extended to other medical problems which involve instantaneous heating or cooling. View full abstract»

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  • Using neural networks and genetic algorithms to enhance performance in an electronic nose

    Page(s): 429 - 439
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    Sensitivity, repeatability, and discernment are three major issues in any classification problem. In this study, an electronic nose with an array of 32 sensors was used to classify a range of odorous substances. The collective time response of the sensor array was first partitioned into four time segments, using four smooth time windowing functions. The dimension of the data associated with each time segment as then reduced by applying the Karhunen-Loeve (truncated) expansion (KLE). An ensemble of the reduced data patterns was then used to train a neural network (NN) using the Levenberg-Marquardt (LM) learning method. A genetic algorithm (GA)-based evolutionary computation method was used to devise the appropriate NN training parameters, as well as the effective database partitions/features. Finally, it was shown that a GA supervised NN system (GANN) outperforms the NN-only classifier, for the classes of the odorants investigated in this study (fragrances, hog farm air, and soft beverages). View full abstract»

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  • A high-temporal resolution algorithm for quantifying organization during atrial fibrillation

    Page(s): 440 - 450
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    Atrial fibrillation (AF) has been described as a "random" or "chaotic" rhythm. Evidence suggests that AF may have transient episodes of temporal and spatial organization. The authors introduce a new algorithm that quantifies AF organization by the mean-squared error (MSE) in the linear prediction between two cardiac electrograms. This algorithm calculates organization at a finer temporal resolution (∼300 ms) than previously published algorithms. Using canine atrial epicardial mapping data, the authors verified that the MSE algorithm showed nonfibrillatory rhythms to be significantly more organized than fibrillatory rhythms (p<.00001). Further, the authors compared the sensitivity of MSE to that of two previously published algorithms by analyzing AF with simulated noise and AF manipulated with vagal stimulation or by adenosine administration to alter the character of the AF. MSE performed favorably in the presence of noise. While all three algorithms distinguished between low and high vagal AF, MSE was the most sensitive in its discrimination. Only MSE could distinguish baseline AF from AF with adenosine. The authors conclude that their algorithm can distinguish different levels of organization during AF with a greater temporal resolution and sensitivity than previously described algorithms. This algorithm could lead to new ways of analyzing and understanding AF as well as improved techniques in AF therapy. View full abstract»

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  • Proposal of a new method for narrowing and moving the stimulated region of cochlear implants: animal experiment and numerical analysis

    Page(s): 451 - 460
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    The authors have proposed the tripolar electrode stimulation method (TESM) for narrowing the stimulation region and continuously moving the stimulation site for cochlear implants. The TESM stimulates the auditory nerve array using three adjacent electrodes which are selected among the electrodes of an electrode array within the lymphatic fluid. Current is emitted from each of the two lateral electrodes and received by the central electrode. The current received by the central electrode is made equal to the sum of the currents emitted from the lateral electrodes. Here, the authors evaluate whether or not TESM works according to a theory which is based on numerical analysis using an electrical equivalent circuit model of the auditory nerve fibers. In this simulation, the sums of the excited model fibers are compared to the compound action potentials (CAPs) which the authors obtained through animal experiments. To identify the main parameter while maintaining the amplitude of the CAP (the sum of the fired fibers), the authors assumed the presence of some parameters from the radial current density profile. In the case of the width value among the parameters being kept constant, the amplitude of the CAP was almost constant; thus, the number of the fired fibers was also almost constant. The width value equals the distance between the points at which the profile of the radial current density of the electrode array and the line of the radial threshold current density of the electrode array intersect. It is possible to determine the measure of the stimulation region or site by controlling the width value and the ratios of the currents emitted from the lateral electrodes. As a result, the authors succeeded in narrowing the stimulation region by controlling the sum of the currents emitted from the two lateral electrodes. Also they succeeded in continuously moving the stimulation site by modifying the currents emitted from the two lateral electrodes. View full abstract»

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  • Electrical stimulation of the auditory nerve: direct current measurement in vivo

    Page(s): 461 - 469
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    Neural prostheses use charge recovery mechanisms to ensure the electrical stimulus is charge balanced. Nucleus cochlear implants short all stimulating electrodes between pulses in order to achieve charge balance, resulting in a small residual direct current (DC). In the present study the authors sought to characterize the variation of this residual DC with different charge recovery mechanisms, stimulation modes, and stimulation parameters, and by modeling, to gain insight into the underlying mechanisms. In an acute study with anaesthetised guinea pigs, DC was measured in four platinum intracochlear electrodes stimulated using a Nucleus(R) CI24M cochlear implant at moderate to high pulse rates (1200-14 500 pulses/s) and stimulus intensities (0.2-1.75 mA at 26-200 μs/phase). Both monopolar and bipolar stimulation modes were used, and the effects of shorting or combining a capacitor with shorting for charge recovery were investigated. Residual DC increased as a function of stimulus rate, stimulus intensity, and pulse width. DC was lower for monopolar than bipolar stimulation, and lower still with capacitively coupled monopolar stimulation. The authors' model suggests that residual DC is a consequence of Faradaic reactions which allow charge to leak through the electrode tissue interface. Such reactions and charge leakage are still present when capacitors are used to achieve charge recovery, but anodic and cathodic reactions are balanced in such a way that the net charge leakage is zero. View full abstract»

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  • A modular micromachined high-density connector system for biomedical applications

    Page(s): 471 - 480
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    This paper presents a high-density, modular, low profile, small, and removable connector system developed using micromachining technologies for biomedical applications. This system consists of a silicon or polyimide electrode with one end in contact with the biological tissue and its back-end supported in a titanium base (12.5 mm in diameter and 2.5 mm in height) that is fixed on the test subject. An external glass substrate (6×6×0.75 mm 3), which supports a flexible polyimide diaphragm and CMOS buffers, is attached to the titanium base whenever electrical contact is required. The polyimide flexible diaphragm contains high-density gold electroplated pads (32 pads, each having an area of 100×100 μm 2 and separated by 150 μm) which match similar pads on the electrode back-end. When vacuum is applied between the two, the polyimide diaphragm deflects and the corresponding gold pads touch, therefore, establishing electrical connection. In vitro electrical tests in saline solution have been performed on a 32-site connector system demonstrating <5 Ω contact resistance, which remained stable after 70 connections, and -55 dB crosstalk at 1 kHz between adjacent channels. In vivo experiments have also confirmed the establishment of multiple contacts and have produced simultaneous biopotential recordings from the guinea pig occipital cortex. View full abstract»

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  • Automatic detection of intraoperative neurological injury

    Page(s): 481 - 483
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    Neurological injuries occurring during high-risk surgical procedures can be detected by monitoring intraoperative evoked potential signals. In this communication, an automatic injury detection algorithm is proposed in which the EP signal is modeled as a pole-zero filter and then the model parameters are applied as inputs to a classifier type neural network. A recognition rate of 96% is achieved using an experimental model of brain injury. View full abstract»

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Aims & Scope

IEEE Transactions on Biomedical Engineering contains basic and applied papers dealing with biomedical engineering. Papers range from engineering development in methods and techniques with biomedical applications to experimental and clinical investigations with engineering contributions.

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Editor-in-Chief
Bin He
Department of Biomedical Engineering