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Biomedical Engineering, IEEE Transactions on

Issue 7 • Date July 1999

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Displaying Results 1 - 15 of 15
  • Anode/cathode make and break phenomena in a model of defibrillation

    Publication Year: 1999 , Page(s): 769 - 777
    Cited by:  Papers (33)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    The goal of this simulation study is to examine, in a sheet of myocardium, the contribution of anode and cathode break phenomena in terminating a spiral wave reentry by the defibrillation shock. The tissue is represented as a homogeneous bidomain with unequal anisotropy ratios. Two case studies are presented in this article: tissue that can electroporate at high levels of transmembrane potential, and model tissue that does not support electroporation. In both cases, the spiral wave is initiated via cross-field stimulation of the bidomain sheet. The extracellular defibrillation shock is delivered via two small electrodes located at opposite tissue boundaries. Modifications in the active membrane kinetics enable the delivery of high-strength defibrillation shocks. Numerical solutions are obtained using an efficient semi-implicit predictor-corrector scheme that allows one to execute the simulations within reasonable time. The simulation results demonstrate that anode and/or cathode break excitations contribute significantly to the activity during and after the shock. For a successful defibrillation shock, the virtual electrodes and the break excitations restrict the spiral wave and render the tissue refractory so it cannot further maintain the reentry. The results also indicate that electroporation alters the anode/cathode break phenomena, the major impact being on the timing of the cathode-break excitations. Thus, electroporation results in different patterns of transmembrane potential distribution after the shock. This difference in patterns may or may not result in change of the outcome of the shock. View full abstract»

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  • The use of the spatial covariance in computing pericardial potentials

    Publication Year: 1999 , Page(s): 778 - 787
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (235 KB)  

    This paper investigates the incorporation of the spatial covariance of the pericardial potentials, assumed known a priori as a regularization function, when computing the pericardial potential distribution from observed body surface potentials. The resulting inverse solutions are compared with those using as a regularization function: (1) the norm of the solution, (2) the norm of the surface Laplacian of the solution, as well as with those based on using the truncated singular value decomposition. The study uses a realistic source model to simulate potentials throughout the QRS-interval. This source is placed in an anatomically accurate inhomogeneous volume conductor model of the torso. The use of a single value of the regularization parameter is shown to be feasible: for data incorporating 2% noise, the use of the spatial covariance is demonstrated to result in a relative error over the entire QRS interval as low as 10%. Major errors are demonstrated to result if the effect of the inhomogeneity of the lungs is ignored. The spatial covariance based inverse is shown to be more robust with respect to the perturbations (noise; inhomogeneity) than the other estimators included in this study. View full abstract»

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  • Canine sternal force-displacement relationship during cardiopulmonary resuscitation

    Publication Year: 1999 , Page(s): 788 - 796
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (202 KB)  

    A viscoelastic model developed to model human sternal response to the cyclic loading of manual cardiopulmonary resuscitation (CPR) (K.G. Gruben et al., J. Biomech. Eng., vol. 115, p. 195-201, 1993) was used to evaluate the properties of canine chests during CPR. Sternal compressions with ventilations after every fifth compression were applied to supine canines (n=7) with a mechanical resuscitation device. The compressions were applied at a nominal rate of 90/min with a peak force near 400 N. From measurements of sternal force, sternal displacement, and tracheal airflow, model parameters were estimated and their dependence on time and lung volume evaluated. The position to which the chest recoiled between compressions changed with time at a mean rate of 1.0 mm/min. Within each ventilation cycle (five compressions) the sternal recoil position decreased by 2.0 cm for each liter of decrease in lung volume. The elastic force and damping decreased with time and decreasing lung volume. Canine and human model parameters were found to be similar despite the notable differences in thoracic anatomy between the species, supporting the continued use of canines as models for human CPR. These parameters may be useful in the development of a model relating sternal compression forces to blood flow during CPR. View full abstract»

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  • Gait phase information provided by sensory nerve activity during walking: applicability as state controller feedback for FES

    Publication Year: 1999 , Page(s): 797 - 809
    Cited by:  Papers (19)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (253 KB)  

    In this study, the authors extracted gait-phase information from natural sensory nerve signals of primarily cutaneous origin recorded in the forelimbs of cats during walking on a motorized treadmill. Nerve signals were recorded in seven cats using nerve cuff or patch electrodes chronically implanted on the median, ulnar, and/or radial nerves. Features in the electroneurograms that were related to paw contact and lift-off were extracted by threshold detection. For four cats, a state controller model used information from two nerves (either median and radial, or ulnar and radial) to predict the timing of palmaris longus activity during walking. When fixed thresholds were used across a variety of walking conditions, the model predicted the timing of EMG activity with a high degree of accuracy (average error=7.8%, standard deviation=3.0%, n=14). When thresholds were optimized for each condition, predictions were further improved (average error=5.5%, standard deviation=2.3%, n=14). The overall accuracy with which EMG timing information could be predicted using signals from two cutaneous nerves for two constant walking speeds and three treadmill inclinations for four cats suggests that natural sensory signals may be implemented as a reliable source of feedback for closed-loop control of functional electrical stimulation (FES). View full abstract»

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  • Modeling of surface myoelectric signals. I. Model implementation

    Publication Year: 1999 , Page(s): 810 - 820
    Cited by:  Papers (49)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    The relationships between the parameters of active motor units (MU's) and the features of surface electromyography (EMG) signals have been investigated using a mathematical model that represents the surface EMG as a summation of contributions from the single muscle fibers. Each MU has parallel fibers uniformly scattered within a cylindrical volume of specified radius embedded in an anisotropic medium. Two action potentials, each modeled as a current tripole, are generated at the neuromuscular junction, propagate in opposite directions and extinguish at the fiber-tendon endings. The neuromuscular junctions and fiber-tendon endings are uniformly scattered within regions of specified width. Muscle fiber conduction velocity and average fiber length to the right and left of the center of the innervation zone are also specified. The signal produced by MU's with different geometries and conduction velocities are superimposed. Monopolar, single differential and double differential signals are computed from electrodes placed in equally spaced locations on the surface of the muscle and are displayed as functions of any of the model's parameters. Spectral and amplitude variables and conduction velocity are estimated from the surface signals and displayed as functions of any of the model's parameters. The influence of fiber-end effects, electrode misalignment, tissue anisotropy, MU's location and geometry are discussed. Part II of this paper will focus on the simulation and interpretation of experimental signals. View full abstract»

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  • Modeling of surface myoelectric signals. II. Model-based signal interpretation

    Publication Year: 1999 , Page(s): 821 - 829
    Cited by:  Papers (61)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (191 KB)  

    For pt. I see ibid., vol. 46, no. 7, p. 810-20 (1999). Experimental electromyogram (EMG) data from the human biceps brachii were simulated using the model described in pt. I of this work. A multichannel linear electrode array, spanning the length of the biceps, was used to detect monopolar and bipolar signals, from which double differential signals were computed, during either voluntary or electrically elicited isometric contractions. For relatively low-level voluntary contractions (10%-30% of maximum force) individual firings of three to four-different motor units were identified and their waveforms were closely approximated by the model. Motor unit parameters such as depth, size, fiber orientation and length, location of innervation and tendonous zones, propagation velocity, and source width were estimated using the model. Two applications of the model are described. The first analyzes the effects of electrode rotation with respect to the muscle fiber direction and shows the possibility of conduction velocity (CV) over- and under-estimation. The second focuses on the myoelectric manifestations of fatigue during a sustained electrically elicited contraction and the interrelationship between muscle fiber CV, spectral and amplitude variables, and the length of the depolarization zone. It is concluded that a) surface EMG detection using an electrode array, when combined with a model of signal propagation, provides a useful method for understanding the physiological and anatomical determinants of EMG waveform characteristics and b) the model provides a way for the interpretation of fatigue plots. View full abstract»

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  • Parallel conductance estimation by hypertonic dilution method with conductance catheter: effects of the bolus concentration and temperature

    Publication Year: 1999 , Page(s): 830 - 837
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (187 KB)  

    The conductance catheter has gained momentum since its introduction in cardiovascular dynamics back in 1980. However, measuring errors are still blurring its clinical acceptance. The main objective here was to study the effects of the injected saline concentration and-temperature on the evaluation of the parallel conductance, G p, and thus, on the correction volume V p. That conductance, G p, and its associated volume, V p, were computed using 167 saline dilution curves obtained with boluses at different concentrations and temperatures, injected in seven anesthetized closed-chest dogs. The excursion of the total conductance relative to the steady-state value during a saline manoeuvre showed good correlation with the injected concentration at both studied temperatures. The reference parallel volume (one reference per dog) was defined as the average value obtained with three successive manoeuvres, at 6-M concentration and at body temperature; therefore, the method acted as its own reference. The variation of V p relative to the reference value was clearly dependent on the injected concentration and on its temperature; dispersion was greater at 22°C than at 40°C. The variability would recognize also other causes, such as uncertainty of the extrapolation procedure and the thoracic redistribution of electrical field lines. As a conclusion, it is recommended to characterize each manoeuvre by its concentration and temperature. Body temperature and 6-M concentration appear as the most recommendable combination for the injectate in most animals. Finally, these results intend to characterize the V p estimation procedure in order to minimize errors. The variability of V p, in different experimental conditions, demonstrated that both concentration and temperature are additional parameters that may modify the G p estimate. View full abstract»

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  • Wavelet transform-based QRS complex detector

    Publication Year: 1999 , Page(s): 838 - 848
    Cited by:  Papers (104)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (173 KB)  

    In this paper, the authors describe a QRS complex detector based on the dyadic wavelet transform (D yWT) which is robust to time-varying QRS complex morphology and to noise. They design a spline wavelet that is suitable for QRS detection. The scales of this wavelet are chosen based on the spectral characteristics of the electrocardiogram (ECG) signal. They illustrate the performance of the D yWT-based QRS detector by considering problematic ECG signals from the American Heart Association (AHA) database. Seventy hours of data was considered. The authors also compare the performance of D yWT-based QRS detector with detectors based on Okada, Hamilton-Tompkins, and multiplication of the backward difference algorithms. From the comparison, results the authors observed that although no one algorithm exhibited superior performance in all situations, the D yWT-based detector compared well with the standard techniques. For multiform premature ventricular contractions, bigeminy, and couplets tapes, the D yWT-based detector exhibited excellent performance. View full abstract»

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  • Subspace regularization method for the single-trial estimation of evoked potentials

    Publication Year: 1999 , Page(s): 849 - 860
    Cited by:  Papers (34)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    A method for the single-trial estimation of the evoked potentials is proposed. The method is based on the so-called subspace regularization approach in which the second-order statistics of the set of the measurements is used to form a prior information model for the evoked potentials. The method is closely related to the Bayesian estimation. The performance of the proposed method is evaluated using realistic simulations. As a specific application the method is applied to the estimation of the target responses in the P300 test. View full abstract»

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  • Multiple window time-frequency distribution and coherence of EEG using Slepian sequences and Hermite functions

    Publication Year: 1999 , Page(s): 861 - 866
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (790 KB)  

    Multiple window (MW) time-frequency analysis (TFA) is a newly developed technique to estimate a time-varying spectrum for random nonstationary signals with low bias and variance. In this paper, the authors describe the application of MW-TFA techniques to electroencephalogram (EEG) and compare the results with those of the conventional spectrogram. They find that the MW-TFA provides them with not only low bias and variance time-frequency (TF) distribution for EEG but also TF coherence estimation between a single realization of EEG recorded from two sites. They also compare the performance of the MW-TFA using two sets of windows, Slepian sequences, and Hermite functions. If care is taken in matching the two windows, the authors find no noticeable difference in the resulting TF representations. View full abstract»

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  • Single-sweep analysis of event-related potentials by wavelet networks-methodological basis and clinical application

    Publication Year: 1999 , Page(s): 867 - 879
    Cited by:  Papers (23)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (479 KB)  

    Trial-to-trial variabilities in event-related potentials (ERP's), which are neglected by investigating averaged ERP's, can be important to establish group-specific effects in clinical studies. Single ERP responses have to be analyzed to quantify these variations. In order to overcome the disadvantages of existing single-sweep estimators, the authors have developed a new procedure based on wavelet networks (WNs) and applied this novel approach in a study concerning attention deficit hyperactivity disorder (ADHD) in children. WN's represent signals as a linear combination of wavelet nodes, i.e., components characterized by time-frequency features related to the wavelet transformation. In single-sweep analysis, each wavelet node is restricted to a specific region of the time-frequency plane during the recursive WN training process. This is achieved by means of tapering and bandpass filtering with Gaussian functions which are automatically adapted and closely related to the Morlet basis wavelet. The time course of a single event-related response can be reliably estimated. Furthermore, the WN method automatically provides well-defined parameters for single event-related responses, respectively ERP trial-to-trial variabilities. In a psychophysiological study on ADHD using auditory evoked potentials (AEPs), latency and amplitude parameters extracted from averaged ERPs did not reveal any significant differences between 25 control and 25 ADHD boys. In contrast, interesting group-specific differences could be established by WN single-sweep analysis. In conclusion, WN single-sweep analysis can be recommended as a sensitive tool for clinical ERP studies which should be applied in addition to the investigation of averaged responses. View full abstract»

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  • Arrays of multielement ultrasound applicators for interstitial hyperthermia

    Publication Year: 1999 , Page(s): 880 - 890
    Cited by:  Papers (9)  |  Patents (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (221 KB)  

    Arrays of multielement ultrasound applicators for interstitial hyperthermia have been developed and tested both in vitro and in vivo. The system includes multielement applicators, a 64 channel RF driving unit, a power measuring unit, a 112 channel multisensor temperature measuring unit, and a water cooling unit. Ninety-five arrays of single-element and nine arrays of three-element ultrasound applicators were designed, built, and characterized by measuring transducer efficiency and ultrasound field distribution. Improved uniformity in the azimuthal direction was achieved by using multiple driving frequencies. In addition, production of ultrasound in a desired sector of the transducer was possible by selecting a suitable frequency. Both in vitro and in vivo experiments showed that 92% of monitored temperature points within the target volume of 30 mm×30 mm×35 mm achieved a therapeutic temperature rise (above 5°C) when an array of five three-element applicators were used. These results indicated that the arrays of multielement ultrasound applicators have distinct advantages over present interstitial hyperthermia modalities in terms of the capability to control the temperature distribution with a large catheter spacing. As a conclusion, the feasibility of a practical arrays of multielement ultrasound applicators for interstitial hyperthermia was demonstrated. View full abstract»

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  • Measurement of the force required to move a neurosurgical probe through in vivo human brain tissue

    Publication Year: 1999 , Page(s): 891 - 894
    Cited by:  Papers (25)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (151 KB)  

    The advent of high-precision magnetic and robotic computer-controlled neurosurgery systems makes it necessary to determine the range of forces that will be encountered by the probes of such devices as they are guided through the brain tissues to intraparenchymal targets. The authors have measured the penetration forces on 2.5-mm spheres and the drag forces on 3.0-mm ventricular shunt catheters advanced 2.0-3.5 cm deep into in vivo human brain tissues (in patients about to have those tissues resected during epilepsy surgery) at rates of ≈0.33 mm s -1. Penetration forces of (8±2) grams were found for the spherical probe once it passed 0.5 cm below the cortical surface, and frictional drags of (2.8±0.3) grams cm -1 were exerted on the catheters. The variable nature of these forces is discussed and the results are compared with earlier studies on experimental animal tissues and brain phantom gelatins. The implications of these results for magnetic and robotic surgery systems are considered. View full abstract»

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  • Indexes for identification of abnormal tremor using computer tremor evaluation systems

    Publication Year: 1999 , Page(s): 895 - 898
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (82 KB)  

    The authors consider methods of formulating indexes to identify abnormalities in tremor appropriate for computerized tremor analysis systems. Characterization of amplitude, frequency, and "harmonicity" are considered as well as how to combine several such characteristics into a single index to discriminate normal from abnormal tremor effectively. The methodological issues discussed here should be of interest to researchers and clinicians working with tremor in general and to both users and developers of computer tremor analysis systems. View full abstract»

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  • Quantification of injury-related EEG signal changes using distance measures

    Publication Year: 1999 , Page(s): 899 - 901
    Cited by:  Papers (11)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (74 KB)  

    Novel indicators based on distance measures are developed and compared to quantify changes in electroencephalogram signal resulting from hypoxic-asphyxic injury. An injury index is derived based on the measures. The Itakura distance-based index is found to have the highest correlation with the long-term outcome as measured by the neurological deficit scores. 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