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Biomedical Engineering, IEEE Transactions on

Issue 5 • Date May 1993

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Displaying Results 1 - 14 of 14
  • Comments, with reply, on "Noninvasive estimation of cardiac output

    Page(s): 504 - 506
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (411 KB)  

    The commenters clarify some aspects of a circuit technique presented with the above-titled paper by W. Welkowitz et al. (ibid., vol.38, p.1100-5, 1991). They conclude that the method cannot provide flow estimation starting from proximal and distal pressure measurements only. The authors show why they believe their procedures to be valid.<> View full abstract»

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  • Evoked otoacoustic emissions: nonlinearities and response interpretation

    Page(s): 500 - 504
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    Evoked otoacoustic emissions (EOAEs) are acoustic signals produced by the inner ear in response to transient acoustic stimuli, and can be recorded in the external auditory canal. Since emissions can be reduced or even abolished by hearing losses of peripheral origin due to trauma and pathology, EOAEs are presently considered as the most sensitive clinical test for assessing the integrity of peripheral hearing. Recordings of emissions evoked in response to transient stimuli are contaminated by an initial artifact which in most clinical environments can be a very serious limitation. For this reason, a nonlinear estimation method called derived nonlinear response (DNLR) is widely used, instead of classical synchronous averaging. The aims of this work are: (i) to justify theoretically the use of the DNLR technique by means of a simple model and (ii) to compare the results obtained from the classical averaging (a linear estimation technique) with those obtained from the DNLR technique. Some suggestions of practical interest are made on the basis of the analysis. View full abstract»

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  • Multichannel ECG data compression by multirate signal processing and transform domain coding techniques

    Page(s): 495 - 499
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    A multilead electrocardiography (ECG) data compression method is presented. First, a linear transform is applied to the standard ECG lead signals, which are highly correlated with each other. In this way a set of uncorrelated transform domain signals is obtained. Then, the resulting transform domain signals are compressed using various coding methods, including multirate signal processing and transform domain coding techniques. View full abstract»

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  • Selective stimulation of peripheral nerve fibers using dual intrafascicular electrodes

    Page(s): 492 - 494
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    The authors have studied activation of nerve fibers by pairs of Pt-Ir wire electrodes implanted within single fascicles of the nerve innervating the gastrocnemius muscle in cats. The purpose of this study was to determine if these intrafascicular electrodes can activate nerve fibers in different fascicles independently of each other and if they can also be used to activate separate subsets of axonal populations within a single fascicle. The average overlap of activated nerve fiber populations was 5.5% between fascicles and 27% within a fascicle, indicating that such selective activation is possible with these electrodes. View full abstract»

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  • Computer-optimization of vascular trees

    Page(s): 482 - 491
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    Arterial branchings closely fulfil several bifurcation rules which are deemed to optimize blood flow. The question is whether these local criteria in conjunction with a general optimization principle can explain the overall structure of an arterial tree. The authors present a model of an arterial vascular tree which is grown on the computer by successively adding terminal vessel segments. Each new terminal segment is connected to the optimum site within the preexisting tree, and the new bifurcation is optimized geometrically. After each step of adding and optimizing, the whole tree is rescaled to meet invariant boundary conditions of pressure and flow at each terminal site. Thus, local geometric optimization is used to induce simultaneously an optimized global structure. The comparison between the model and real coronary arterial trees shows good agreement regarding structural appearance, morphometric parameters, and pressure profiles.<> View full abstract»

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  • Mathematical analysis and computer simulation of the respiratory system in the newborn infant

    Page(s): 475 - 481
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    A mathematical model of neonatal respiratory control which can be used to simulate the system under different physiological conditions is proposed. The model consists of a continuous plant and a discrete controller. Included in the plant are lungs, body tissue, brain tissue, a cerebrospinal fluid compartment, and central and peripheral receptors. The effect of shunt in the lungs is included in the model, and the lung volume and the dead space are time varying. The controller utilizes outputs from peripheral and central receptors to adjust the depth and rate of breathing, and the effects of prematurity of peripheral receptors are included in the system. Hering-Breuer-type reflexes are embodied in the controller to accomplish respiratory synchronization. The model is examined and its simulation results under test conditions in hypoxia and hypercapnia are presented. View full abstract»

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  • Implementation of ultrasound time-domain cross-correlation blood velocity estimators

    Page(s): 468 - 474
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (499 KB)  

    The implementation of real-time blood velocity estimators using time-domain cross-correlation is investigated. The basic algorithm for stationary echo canceling, cross-correlation estimation and subsequent velocity estimation is presented. Sampled data acquired at rates of approximately 20 MHz are used in the algorithm, imposing a heavy burden on the signal processing hardware. The algorithm is analyzed with regard to the high sampling frequency, and a method for performing real-time high-speed-movement and cross-correlation is suggested. Implementation schemes based on using the sign of the data as well as the full precision are proposed. From an analysis of the process it is concluded that the sign data implementation can attain real-time processing. This can also be obtained for the full precision data, but at the expense of using a number of dedicated signal processing chips. Both implementations suggested can handle the estimation of velocities for A-lines acquired from multiple directions. View full abstract»

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  • Dynamic formant tracking of noisy speech using temporal analysis on outputs from a nonlinear cochlear model

    Page(s): 456 - 467
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    The authors take a modeling approach to studying representation of formant frequencies of spoken speech and speech in noise in the temporal responses of the peripheral auditory system. On the basis of the properties of the representation, they have devised and evaluated a cross-channel correlation algorithm and an interpeak interval analysis for automatic formant extraction of speech which is strongly dynamic in acoustic characteristics and is embedded in noise. The basilar membrane model used in this study contains laterally coupled damping elements, which are made monotonically dependent on the spatial distribution of the short-term power in the outputs of the model. Efficient digital implementation and the related salient numerical properties of the model are described. Simulation results from the model in response to speech and speech in noise illustrate temporal response patterns that are tonotopically organized in relation to speech formant parameters with little influence by the noise level. By utilizing such relations the devised cross-channel correlation algorithm is shown to be capable of accurately tracking formant movements in spoken syllables and sentences. View full abstract»

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  • Linear and nonlinear techniques for the deconvolution of hormone time-series

    Page(s): 440 - 455
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    Pulsatile hormone secretion is usually investigated by measuring hormone concentration in samples of peripheral plasma. Here, the deconvolution of hormone time series to reconstruct the instantaneous secretion rate of glands is considered. Various techniques are discussed and compared in order to overcome the ill-conditioning of the problem and reduce the computational burden. In particular, linear techniques based on least squares, maximum a posteriori (MAP) estimation, and Wiener filtering are compared. A new nonlinear MAP estimator that keeps into account the non-Gaussian distribution of the unknown signal is worked out and shown to yield the best results. The performances of the algorithms are tested on simulated time series as well as on series of luteinizing hormone. View full abstract»

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  • The mosaic electrical characteristics of the skin

    Page(s): 434 - 439
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (630 KB)  

    The authors constructed a suction microelectrode with a 200- mu m internal diameter and performed several tests on two male subjects. It was found that the average skin impedance on the forearm was larger than the average impedance on the palm and that the ratio between the maximal and minimal skin impedance was larger for the forearm than for the palm. For both the magnitude and variance of skin impedance decreased with increasing stimulus frequency. The density of low-impedance points observed on the forearm and palm was consistent with the density of DC current pathways through the skin as indicated by traces left on 1-cm 2 Ag electrodes. The ratio between the highest and lowest impedances decreased as temperature decreased. The authors were not able to break down the skin using the suction microelectrode. Tests suggest that breakdown is of thermal nature, and that the thermal capacitance of the saline in the suction microelectrode prevents the temperature of the underlying skin from increasing very rapidly, increasing the breakdown voltage. View full abstract»

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  • A bidomain model with periodic intracellular junctions: a one-dimensional analysis

    Page(s): 424 - 433
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    The classical bidomain model of cardiac tissue views the intracellular and extracellular (interstitial) spaces as two coupled but separate continua. In the present study, the classical bidomain model has been extended by introducing a periodic conductivity in the intracellular space to represent the junction discontinuity between abutting myocytes. In this model the junction region of a myocyte is represented in a way that permits variation of junction size and conductivity profile. Employing spectral techniques, a method is developed for solving the coupled differential equations governing the intracellular and extracellular potentials in a tissue preparation of finite dimensions. Different spectral representations are used for the aperiodic intra- and extracellular potentials (finite Fourier integral transform) and for the periodic intracellular conductivity (Fourier series). As a first application of the method, the response of a 50-cell, single interior fiber to a defibrillating current is examined under steady-state conditions. Transmembrane as well as intra- and extracellular potential distributions along the fiber have been calculated. View full abstract»

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  • Noninvasive measurement of current in the human body for electromagnetic dosimetry

    Page(s): 418 - 423
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    Minimally perturbing, resistive, nonferrous probes were developed for noninvasively measuring hazardous currents induced in the human body by electromagnetic fields at 1-200 MHz. Each probe has a resistive toroidal coil that is placed around the leg or other body member. An electrostatic shield is required to limit capacitive coupling. A new shielded test fixture provides TEM fields for calibration with a voltage standing wave ratio (VSWR) less than 1.1 from 1 to 200 MHz. A man-sized phantom was exposed to the near field of a vertical monopole antenna at 29.9 MHz, and the value of the current measured in the leg with the probe is in reasonable agreement with measured heating. Analyses and experiments show that commercial ferrous current probes modify the circuit in which they are used, changing the current being measured. Less change is caused by the authors' nonferrous current probes. View full abstract»

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  • Temperature distribution in tissues from a regular array of hot source implants: an analytical approximation

    Page(s): 408 - 417
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    An approximate analytical model based on the bioheat transfer equation is derived and used to calculate temperature within a perfused region implanted regularly with dielectrically coated hot source implants. The effect of a regular array of mutually parallel heat sources of cylindrical shape is approximated by idealizing one of the boundary conditions. The solution is in terms of modified Bessel functions. In calculating the temperature of each thermoregulating source in the array, the steady state power balance is enforced. The important feature of the model is that the finite size of implant diameter and its dielectric coating can be incorporated. The effect of thickness and thermal conductivity of the coating on the source and tissue temperatures along with various other interesting features are deduced from this model. The analytically calculated implant and tissue temperatures are compared with those of a numerical 3-D finite difference model. The analytical model also is used to define a range of parameters such that minimal therapeutic temperatures will be achieved in the implanted volume without exceeding prescribed maximum temperatures. View full abstract»

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  • Evanescent-mode applicators (EMA) for superficial and subcutaneous hyperthermia

    Page(s): 397 - 407
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    Evanescent-mode waveguide aperture applicators are proposed for hyperthermic treatments of superficial and subcutaneous tissues. They consist of air-filled waveguide segments that work below the cutoff frequency and therefore support only evanescent transverse modes. These are excited by radiators of suitable symmetry and configuration to produce modal heating fields of selected cross-sections. This field emerges from the waveguide active aperture and enters the tissue to be heated through an air gap. These devices work in a very large range of frequencies and are extremely simple to manufacture, even with a variety of cross-section sizes and shapes, because of their air-filled feature. This enables good heating field flexibility with improved penetration to be obtained. Their operation is safe and practical also on irregular and curved tissue surfaces. 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