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Biomedical Engineering, IEEE Transactions on

Issue 4 • Date April 1995

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Displaying Results 1 - 13 of 13
  • Electric field stimulation of excitable tissue

    Publication Year: 1995 , Page(s): 329 - 336
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (778 KB)  

    Examines the transmembrane voltage response of an unmyelinated fiber to a stimulating electric field from a point current source. For subthreshold conditions, analytic expressions for the transmembrane potential, v m, are developed that include the specific effects of fiber-source distance, h, and time from the onset of the stimulus, T. Suprathreshold effects are determined for two examples by extending the analytical results with a numerical model. The v m, response is a complex evolution in time, especially for small h, that differs markedly from the "activating function". In general, the subthreshold response is a good predictor of the wave shape of the suprathreshold v m but a poor predictor of its magnitude. The subthreshold response also is a good (but not a precise) predictor of the region where excitation begins. View full abstract»

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  • A method for determining the driving currents for focused stimulation in the cochlea

    Publication Year: 1995 , Page(s): 337 - 342
    Cited by:  Papers (3)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (587 KB)  

    A pseudo-inverse technique has been applied to a lumped-element model of the first turn of an implanted cochlea of a guinea pig. The method calculates the currents necessary to focus or distribute stimuli in desired patterns across the location of the family of auditory nerve cells in the implanted ear. Studies in animals are being undertaken to validate the technique. View full abstract»

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  • Comparative simulation of excitation and body surface electrocardiogram with isotropic and anisotropic computer heart models

    Publication Year: 1995 , Page(s): 343 - 357
    Cited by:  Papers (29)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1610 KB)  

    Comparative simulations between isotropic and anisotropic computer heart models were conducted to study the effects of myocardial anisotropy on the excitation process of the heart and on body surface electrocardiogram. The isotropic heart model includes atria, ventricles, and a special conduction system, and is electrophysiologically specified by parameters relative to action potential, conduction velocity, automaticity, and pacing. The anisotropic heart model was created by incorporating rotating fiber directions into the ventricles of the isotropic heart model. The orientation of the myocardial fibers in the ventricles of the model was gradually rotated counterclockwise from the epicardial layer to the endocardial layer for a total rotation of 90°. The anisotropy of conduction velocity and intracellular electric conductivity was included in the simulation. Comparative simulations of the normal heart, LBBB, and RBBB showed no significant differences between the two models in the excitation processes of the whole heart or in the body surface electrocardiograms. However, it was easier to induce ventricular fibrillation in the anisotropic model than in the isotropic model. The comparative simulation is useful for investigating the effects of myocardial anisotropy at the whole heart level and for evaluating limitations of the isotropic heart model. View full abstract»

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  • Distribution of aortic mechanical prosthetic valve closure sound model parameters on the surface of the chest

    Publication Year: 1995 , Page(s): 358 - 370
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (984 KB)  

    If has been previously proposed that heart valve closure sounds can be modeled by a sum of decaying sinusoids, based on the hypothesis that the heart cavity, heart walls, major vessels, and other structures in the chest constitute a frequency selective linear acoustic system and this system is excited by the rapidly decelerating valve occluder. In this study, the distribution of the parameters of this model for the second heart sound is investigated. For this purpose, heart sounds of 10 patients who have a St. Jude-type bileaflet mechanical heart valve prosthesis in the aortic position are recorded. Recordings are performed at 12 different locations on the surface of the chest. To reliably assign representative parameters to each recording site, signal averaging, model order selection, and a special filtration technique are employed. The results of the analyses are discussed in relation to the above hypothesis on the heart sound generation mechanism. It is observed that site-to-site variation of frequencies of modes does not exceed the accuracy limit of proposed analysis method, but energies of these modes vary on the surface of the chest, and as a result of statistical analysis, it appears that energy of some modes are significantly different between two recording sites. View full abstract»

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  • Multiple drug hemodynamic control by means of a supervisory-fuzzy rule-based adaptive control system: validation on a model

    Publication Year: 1995 , Page(s): 371 - 385
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1471 KB)  

    A control device that uses an expert system approach for a two input-two output system has been developed and evaluated using a mathematical model of the hemodynamic response of a dog. The two inputs are the infusion rates of two drugs: sodium nitroprusside (SNP) and dopamine (DPM). The two controlled variables are the mean arterial pressure and the cardiac output. The control structure is dual mode, i.e., it has two levels: a critical conditions (coarse) control mode and a noncritical conditions (fine) control mode. The system switches from one to the other when threshold conditions are met. Different "controller parameters sets"-including the values. For the threshold conditions-can be given to the system which will lead to different controller outputs. Both control modes are rule-based, and supervisory capabilities are added to ensure adequate drug delivery. The noncritical control mode is a fuzzy logic controller. The system includes heuristic features typically considered by anesthesiologists, like waiting periods and the observance of a "forbidden dosage range" for DPM infusion when used as an inotrope. An adaptation algorithm copes with the wide range of sensitivities to SNP found among different individuals, as well as the time varying sensitivity frequently observed in a single patient. The control device is eventually tested on a nonlinear model, designed to mimic the conditions of congestive heart failure in a dog. The test runs show a highest overshoot of 3 mmHg with nominal SNP sensitivity. When tested with different simulated SNP sensitivities, the controller adaptation produces a faster response to lower sensitivities, and reduced oscillations to higher sensitivities. The simulations seem to show that the system is able to drive and adequately keep the two hemodynamic variables within prescribed limits. View full abstract»

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  • The dynamic response of the cat ankle joint during load-moving contractions

    Publication Year: 1995 , Page(s): 386 - 393
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (866 KB)  

    The dynamic response of the cat's ankle joint during load-moving activation of the medial gastrocnemius was determined. Sinusoidal-input oscillations of ankle plantar flexion were performed by the muscle at frequencies ranging from 0.4 to 5 Hz against a 10-N load acting via a cable through a pulley with a 2 cm radius. This was followed by sinusoidal muscle length changes against the same load while excluding the joint. The frequency responses of the two conditions were compared and decomposed in terms of their relative phase and gain, and best-fit pole-zero models to yield the dynamic model of the joint isolated from the muscle properties. The muscle displacement transfer function M(jω) was characterized as two sets of double poles at 2.1 and 3.2 Hz, with a pair of zeros at 0.92 and 20 Hz, and pure time delay of 8 ms. The joint model J(jω) was obtained by adding a pole at 5 Hz and a zero at 13 Hz. It was concluded that the ankle joint acts as a lag system, introducing significant increase in the phase lag between stimulus input and mechanical output without affecting the frequency-dependent attenuation of gain. Average harmonic distortion was less than 5% in all cases. This particular finding reveals that, despite its inherently nonlinear mechanical characteristics, the joint introduces no degradation in the simplified linear behavior of the muscle-joint system. This model is useful in the design of systems employing electrical stimulation to restore movement to limbs paralyzed by spinal cord injury or stroke. In this application, it is suggested that a linear systems approach may be reasonable, but that the joint's dynamic response decreases the control system design stability margins of the muscle-joint unit. The joint model J(jω), albeit obtained from a condition in which only one muscle was activated, could be used in complex conditions where several muscles are cocontracting independently as agonists or antagonists to modify the - - torque, angle, or stiffness of the joint. View full abstract»

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  • Influence of flow pattern on the parameter estimates of a simple breathing mechanics model

    Publication Year: 1995 , Page(s): 394 - 402
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (950 KB)  

    The first-order model of breathing mechanics is widely used in clinical practice to assess the viscoelastic properties of the respiratory system. Although simple, this model takes the predominant features of the pressure-flow relationship into account but gives highly systematic residuals between measured and model-predicted variables. To achieve a better fit of the entire data set, an approach hypothesizing deterministic time-variations of model parameters, summarized by information-weighted histograms was recently proposed by Bates and Lauzon (1992). The present study uses flow and pressure data measured in intensive care patients to evaluate the real potential of this approach in clinical practice. Information-weighted histograms of the model parameters, estimated by an on-line identification algorithm, were first constructed by taking into account the parameter percentage standard deviations. Then, the influence of the respiratory flow pattern on the calculated histograms was evaluated by the Kolmogorov-Smirnov statistical test. The results show that the method gives good reproducibility under stable experimental conditions. In addition, for a given airflow waveform; an increase in respiratory frequency shifts the histograms representing time-varying viscous properties strongly versus lower values, whereas it shifts the histograms representing time-varying elastic properties slightly versus higher values. On the other hand, the same histograms were highly dependent on the airflow waveform, especially for the viscous properties. Even in a limited experimental work, in all the conditions considered, the method provides results which agree well with the physiological knowledge of nonlinear and multicompartment behavior of respiratory mechanics. View full abstract»

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  • Echographic image mean gray level changes with tissue dynamics: a system-based model study

    Publication Year: 1995 , Page(s): 403 - 410
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (845 KB)  

    In echography, several groups have reported a systematic decrease in the total backscattering intensity or image mean gray level during myocardial contraction with a minimum at end-systole and maximum at end-diastole. In order to investigate this phenomenon, the authors use a three-dimensional inhomogeneous continuum model to mimic the tissue as a collection of cells that scatter the acoustic wave due to their individual impedance. The mathematical analysis clearly shows the relationship between the mean gray level changes and the size, orientation, and deformation of the cells that compose the tissue, as well as the frequency of the transducer. Using a myocardial model example, the mean gray level changes reported in the literature during contraction are described in terms of changes in orientation and deformation of cardiac fibers. The model is simple and should set the ground for further study and analysis of speckle pattern changes during tissue motion. View full abstract»

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  • Application of linear and nonlinear time series modeling to heart rate dynamics analysis

    Publication Year: 1995 , Page(s): 411 - 415
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    The linear autoregressive (AR) model is often used to investigate the pathophysiologic mechanisms controlling heart rate (HR) dynamics. This study implemented parametric models new to this field to determine if a more appropriate HR dynamics modeling structure exists. The linear AR and autoregressive-moving average (ARMA) models, and the nonlinear polynomial autoregressive (PAR) and bilinear (BL) models were fit to instantaneous HR time series obtained from nine subjects in the supine position. Model orders were determined by the Akaike Information Criteria (AIC). Model residual variance was used as the primary intermodel comparison criterion, with significance evaluated by a λ 2 distributed statistic. The BL model best represented the HR dynamics, as its residual variance was significantly (p<0.05) smaller than that of the corresponding AR model for nine out of nine data sets. In all cases, the BL model had a smaller residual variance than either the ARMA or PAR models. The bilinear model was ineffective at data forecasting, however, the authors show that this cannot reflect BL model validity because poor prediction is inherent to the BL model structure. The apparent superiority of the nonlinear bilinear model suggests that future heart rate dynamics studies should put greater emphasis on nonlinear analyses. View full abstract»

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  • Coordinate system matching for neuromagnetic and morphological reconstruction overlay

    Publication Year: 1995 , Page(s): 416 - 420
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (578 KB)  

    The overlay of functional and morphological images is an essential tool for advanced and improved functional diagnosis showing the correlation between spatial structures or lesions and functional areas. The authors present an improved coordinate system matching technique. The well known method of three orthogonal coils combined in one coilset for an angular-independent measure is validated for the use of first- or higher order gradiometers instead of magnetometers. The coilset localization procedure was modified with lock-in detection and current feedback for better long range sensitivity. Real measurements with the 31-channel Philips-MEG system have been carried out. A very good localization accuracy below the measuring area with deviations below 2 mm was found. For coordinate system matching, a 3-D cursor with surface images from segmented MR-data was implemented and an optimized, weighted least squares fit transformation algorithm between functional and morphological systems was developed. The resulting transformations consist of weighted shifts and best-fit rotations and lead to deviations of marker positions in the mm range, depending mainly on the spatial accuracy of the marker fixation. View full abstract»

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  • Detection of loss of cerebral vascular tone by correlation of arterial and intracranial pressure signals

    Publication Year: 1995 , Page(s): 420 - 424
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (582 KB)  

    With the use of a laboratory model, arterial and intracranial pressure signals were obtained under conditions of intact regulation of cerebral blood flow and massive dilation. During elevated intracranial pressure and intact regulation, positive pressure inhalation appears to briefly occlude venous flow into the cranial sinuses during inspiration. As a result, the intracranial pressure and arterial pressure signals are not similar. In contrast, when maximal dilation causes failure of regulation of cerebral blood flow, the intracranial pressure signal is approximately proportional to the arterial pressure signal. Comparison of the cross-correlation function derived from the intracranial and arterial pressure signals to the autocorrelation function of the arterial signal reveals that the two correlation functions are: (1) different during intact regulation and (2) nearly identical during dilation induced failure of regulation of cerebral blood flow. View full abstract»

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  • Latency measurement improvement of P100 complex in visual evoked potentials by FMH filters

    Publication Year: 1995 , Page(s): 424 - 428
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    The ensemble average of pattern shift visual evoked potentials (PSVEPs) signals is seriously affected by random latency variations encountered in each individual sweep which is modeled as a continuous signal with linear segments and well-shaped triangular peaks. This effect is causing the smoothed peaks of the averaged PSVEP waveforms. It is the authors objective to restore the degraded peaks and provide accurate information about their exact location. The method used is based on nonlinear filtering of the FIR-median hybrid (FMH) type and is recommended as a postfiltering process to the well-known averaging methods of recovering PSVEP signals from noise by time-locking to stimuli. The new technique, tested in signals from clinical observations, has proven very promising. View full abstract»

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  • Brain maturation estimation using neural classifier

    Publication Year: 1995 , Page(s): 428 - 432
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    Quantitative electroencephalographic (EEG) signal analysis has revealed itself as an important diagnostic tool in the last few years. Through the use of signal processing techniques, new quantitative representations of EEG data are obtained. To automate the diagnosis, a problem of supervised classification must be solved on these. Artificial neural networks provide an alternative to more traditional classifier systems for this task. The authors perform a comparison between several classifiers in a particular problem, the brain maturation prediction. The data preprocessing/feature extraction process and the methodology for making the comparison are described. Performance of the methods is evaluated in terms of estimated percentage of correctly classified subjects. 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