By Topic

Biomedical Engineering, IEEE Transactions on

Issue 4 • Date April 2000

Filter Results

Displaying Results 1 - 16 of 16
  • A simulation of the SA node by a phase response curve-based model of a two-dimensional pacemaker cells array

    Publication Year: 2000 , Page(s): 425 - 434
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (574 KB)  

    This paper presents a simulation of the sino-atrial (SA) node by a two-dimensional pacemaker cells array model, based on phase response curve (PRC) interaction. This simple model of the cardiac pacemaker cells, involves only the most basic functional properties, which play a direct role in the determination of the SA node rhythm. The two most relevant functional properties of the pacemaker cells are: the intrinsic cycle length, an "internal" feature of each pacemaker cell, and the PRC, an "overall collective" function. The PRC contains the "information" about the type of interactions of each pacemaker cell with the outside world (i.e., interaction with neighboring cells, external stimulus, etc.), and "strength" of the interaction (strong, weak, etc.). The authors' studied the spatial interaction among a large number of pacemaker cells (15×15), as a function of the regional variation of cells properties, the "electrical" coupling between cells (the PRC), and the appearance of regions with abnormal cycle lengths. The authors investigated the influence of those parameters on the mutual interaction between the pacemaker cells, on the activation pattern and conduction time of the array, and on a pseudo-electrocardiogram (ECG) signal. This study demonstrates that by representing the pacemaker cells in the SA node by only two fundamental features, and by applying a simple physical-mathematical model, one can create a global picture of the SA node system. This enables one to explore physiological phenomena related to the genesis and maintenance of the SA node activity, and to gain insight into the conditions which predispose the SA node instability, and conduction disturbances. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Perturbations in hyperthermia temperature distributions associated with counter-current flow: numerical simulations and empirical verification

    Publication Year: 2000 , Page(s): 435 - 443
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (578 KB)  

    Two numerical techniques are used to calculate the effect of large vessel counter-current flow on hyperthermic temperature distributions. One is based on the Navier-Stokes equation for steady-state flow, and the second employs a convective-type boundary condition at the interface of the vessel walls. Steady-state temperature fields were calculated for two energy absorption rate distributions (ARD) in a cylindrical tissue model having two pairs of counter-current vessels (one pair with equal diameter vessels and another pair with unequal diameters). The first assumed a uniform ARD throughout cylinder; the second ARD was calculated for a tissue cylinder inside an existing four antenna radiofrequency (RF) array. A tissue equivalent phantom was constructed to verify the numerical calculations. Temperatures induced with the RF array were measured using a noninvasive magnetic resonance imaging technique based on the chemical shift of water. Temperatures calculated using the two numerical techniques are in good agreement with the measured data. The results show: (1) the convective-type boundary condition technique reduces computation time by a factor of ten when compared to the fully conjugated method with little quantitative difference (∼0.3°C) in the numerical accuracy and (2) the use of noninvasive magnetic resonance imaging (thermal imaging) to quantitatively access the temperature perturbations near large vessels is feasible using the chemical shift technique. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Parametric studies of human thermal mechanisms and measurements

    Publication Year: 2000 , Page(s): 444 - 451
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (207 KB)  

    A systematic methodology is proposed for mathematically quantifying the effects of measurement inaccuracies due to instrument uncertainty in a human calorimetry project. Human thermal mechanisms are poorly understood at the systems level and this study investigates the importance of these mechanisms quantitatively. The proposed methodology uses sensitivity derivatives combined with sensor accuracies to quantify the effect of each heat transfer mechanism contributing to the errors in the system equations. The method is applicable to any differentiable model to be validated by experimentation. To illustrate the methodology, two example cases, a reclining nude resting subject and a reclining clothed working subject, are analyzed. The calculated expected errors clearly suggest specific modifications. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Nonlinear system identification and overparameterization effects in multisensory evoked potential studies

    Publication Year: 2000 , Page(s): 472 - 486
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    Traditional signal processing techniques have not been suitable in establishing contributions from different sensory paths in multisensory evoked potentials. In this paper, a nonlinear modeling technique is proposed to demonstrate the possible mechanisms of interaction between sensory paths. The nonlinear autoregressive with exogenous inputs (NARX) model is explored to establish a relationship between electrical activities of the brain obtained by unimodal and by bimodal stimulation. The intersensory phenomenon concept is extended using nonlinear system theory and applied to show the possible interactions between the visual and auditory sensory paths. In addition, the paper addresses the compensation phenomenon caused by overparameterization in the NARX algorithm when it is applied to event-related potentials. It is hoped that the nonlinear modeling approach will generate hypotheses about the intersensory interaction phenomenon, improving and advancing its theoretical formulation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Vectorcardiographic loop alignment and the measurement of morphologic beat-to-beat variability in noisy signals

    Publication Year: 2000 , Page(s): 497 - 506
    Cited by:  Papers (15)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (301 KB)  

    The measurement of subtle morphologic beat-to-beat variability in the electrocardiogram (ECG)/vectorcardiogram (VCG) is complicated by the presence of noise which is caused by, e.g., respiration and muscular activity. A method was recently presented which reduces the influence of such noise by performing spatial and temporal alignment of VCG loops. The alignment is performed in terms of scaling, rotation and time synchronization of the loops. Using an ECG simulation model based on propagation of action potentials in cardiac tissue, the ability of the method to separate morphologic variability of physiological origin from respiratory activity was studied. Morphologic variability was created by introducing a random variation in action potential propagation between different compartments. The results indicate that the separation of these two activities can be done accurately at low to moderate noise levels (less than 10 μV). At high noise levels, the estimation of the rotation angles was found to break down in an abrupt manner. It was also shown that the breakdown noise level is strongly dependent on loop morphology; a planar loop corresponds to a lower breakdown noise level than does a nonplanar loop. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A new method for the extraction of fetal ECG from the composite abdominal signal

    Publication Year: 2000 , Page(s): 507 - 516
    Cited by:  Papers (60)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (274 KB)  

    We developed a wavelet transform-based method to extract the fetal electrocardiogram (ECG) from the composite abdominal signal. This is based on the detection of the singularities obtained from the composite abdominal signal, using the modulus maxima in the wavelet domain. Modulus maxima locations of the abdominal signal are used to discriminate between maternal and fetal ECG signals. Two different approaches have been considered, In the first approach, at least one thoracic signal is used as the a prior to perform the classification whereas in the second approach no thoracic signal is needed, A reconstruction method is utilized to obtain the fetal ECG signal from the detected fetal modulus maxima. The proposed technique is different from the classical time-domain methods, in that we exploit the most distinct features of the signal, leading to more robustness with respect to signal perturbations. Results of experiments with both synthetic and real ECG data have been presented to demonstrate the efficacy of the proposed method. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An ultrasonic method for noninvasive estimation of vascular impedance to an absolute level: in vitro validation of the relationship between impedance and phase velocity

    Publication Year: 2000 , Page(s): 517 - 526
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (174 KB)  

    Vascular impedance is a quantity that characterizes the properties of the vascular bed. Assuming Newtonian fluid, laminar flow and linear system, impedance is related to phase velocity. The agreement between theoretical relationship and measured data is evaluated in an in vitro study. The setup consist of a computer-controlled flow generator, a variable fluid impedance and a measuring section. Phase velocity is calculated from multiple recorded vessel pulsations detected by ultrasonic pulse-echo technique. The reference impedance is calculated from simultaneously measured high-fidelity pressure and flow data. The impedance is analyzed in the range of 1-40 Hz with 1-Hz resolution. The evaluation of the noninvasive ultrasonic technique is focused on the resonance frequencies and the characteristic impedance. No significant difference (p>0.05) is found in the resonance frequencies nor in the characteristic impedance. However, the impedance below 5 Hz is underestimated and the extension of the measuring section causes spatial averaging effects with reduced frequency resolution. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Radiowave propagation from a tissue-implanted source at 418 MHz and 916.5 MHz

    Publication Year: 2000 , Page(s): 527 - 534
    Cited by:  Papers (67)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (467 KB)  

    Tissue-implanted ultra-high frequency (UHF) radio devices are being employed in both humans and animals for telemetry and telecommand applications. This paper describes the experimental measurement and electromagnetic modeling of propagation from 418-MHz and 916.5-MHz sources placed in the human vagina. Whole-body homogeneous and semi-segmented software models were constructed using data from the Visible Human Project. Bodyworn radiation efficiencies for a vaginally placed 418-MHz source were calculated using finite-difference time-domain and ranged between 1.6% and 3.4% (corresponding to net body losses of between 14.7 and 18.0 dB). Greater losses were encountered at 916.5 MHz, with efficiencies between 0.36% and 0.46% (net body loss ranging between 23.4 and 24.4 dB). Practical measurements mere in good agreement with simulations, to within 2 dB at 418 MHz and 3 dB at 916.5 MHz. The degree of tissue-segmentation for whole-body models was found to have a minimal effect on calculated azimuthal radiation patterns and bodyworn radiation efficiency, provided the region surrounding the implanted source was sufficiently detailed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Theoretical model for an MRI radio frequency resonator

    Publication Year: 2000 , Page(s): 535 - 546
    Cited by:  Papers (17)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (697 KB)  

    A theoretical model is described for a magnetic resonance imaging (MRI) radio-frequency resonator (an MRI "coil") that is useful at ultrahigh frequencies. The device is a "TEM resonator" which is based on a concept originally proposed by Roschmann (1988). The coil comprises a circular cavity-like structure containing several coaxial transmission lines operating in a transverse electromagnetic (TEM) mode. The model developed herein treats the empty coil and is based on multiconductor transmission line theory. This work generalizes and extends similar analyses of the device by Roschmann (1995) and Chingas and Zhang (1996). The model employs explicit calculation of per-unit-length parameters for TEM lines having arbitrary geometries. Calculations of the resonator's frequency response are found to compare well with measurements. Fields produced by linear (single-point) and quadrature drive are also computed and compared to images of low-permittivity phantoms. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A method for the reconstruction of ground reaction force-time characteristics during gait from force platform recordings of simultaneous foot falls

    Publication Year: 2000 , Page(s): 547 - 551
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (102 KB)  

    This paper proposes a method for the reconstruction of foot-ground reaction forces from force platform recordings of two constructive footfalls. The reconstruction algorithm uses zero-derivative criterion (inflection point) to detect contralateral foot contacts and subtracts contralateral forces from the combined force-time curve in order to reconstruct force-time data. Experimental results suggest that the method can be applied to separate accurately foot-specific gait forces from corrupted force-time data as a result of incorrect stepping on a force platform. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Compensation of the differential floating capacitance between dual microelectrodes

    Publication Year: 2000 , Page(s): 551 - 555
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB)  

    A circuit for compensating the floating differential capacitance appearing between two recording microelectrodes is presented. It is shown how this floating capacitance can be neutralized so that current in any microelectrode can be injected without any significant crosstalk picked up by the other. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Compensating for window effects in the calculation of spectrographic instantaneous bandwidth

    Publication Year: 2000 , Page(s): 556 - 558
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB)  

    Exact results derived by Cohen and Lee (1988-1990) are used to study the distortion induced by the window in the computation of instantaneous bandwidth via the spectrogram. These concepts have been recently used in an interesting study regarding lesion-induced blood flow disturbances, where an approximation was made to compensate for the window effects. We show that this compensation is accurate for stationary signals, but becomes increasingly poorer as the signal becomes less stationary (e.g., large frequency modulations). We propose an alternative technique to reduce the window distortions, and point out the use of other time-frequency distributions that do not suffer such distortions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Correlation of esophageal conductance measurements with aortic and left ventricular diameters and stroke volume

    Publication Year: 2000 , Page(s): 559 - 564
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (147 KB)  

    Esophageal conductance measurements were correlated with hemodynamic events in 9 dogs chronically instrumented for measurement of left ventricular (LV) and aortic pressures, LV short axis and descending aortic diameters, and aortic blood flow. A four-electrode conductance catheter was positioned in the esophagus. Both an internal and an internal/external configuration were examined during anesthesia with hemodilution, pulmonary lavage and dobutamine infusion. LV stroke volume was altered by caval occlusion at each intervention. Stroke conductance was highly correlated to aortic or LV diameters and stroke volume over a range of diameters depending on the electrode configuration. Esophageal conductance measurements are directly influenced by local hemodynamic events adjacent to the site of measurement. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fusion of body surface potential and body surface Laplacian signals for electrocardiographic imaging

    Publication Year: 2000 , Page(s): 452 - 462
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    Various approaches to the solution to the inverse problem of electrocardiography have been proposed over the years. Recently, the use of inverse algorithms using measured body surface Laplacians has been proposed, and in various studies this technique has been shown to outperform the traditional use of body surface potentials in certain model problems. In this paper, the authors compare the use of body surface potentials and body surface Laplacians on two model problems with different assumed cardiac sources. For the spherical cap model problems with an anterior source, the epicardial estimates using body surface potentials had smaller average relative errors than when body surface Laplacians were used. For the spherical cap model problems with a posterior source, the epicardial estimates using body surface potential or body surface Laplacian sensors generally produced similar relative errors. For the radial dipole model, the epicardial estimates using body surface Laplacians had smaller errors than when body surface potentials were used. The authors introduce a fusion algorithm that combines the different types of signals and generally produces a good estimate for both model problems View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Prediction of neural excitation during magnetic stimulation using passive cable models

    Publication Year: 2000 , Page(s): 463 - 471
    Cited by:  Papers (6)  |  Patents (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    A method for predicting neural excitation during magnetic stimulation using passive cable models has been developed. This method uses the information of the threshold capacitor voltage for magnetic stimulation coils to determine the equivalent excitation thresholds for the passive transient (PT) and passive steady-state (PSS) cable models as well as for the activating function. The threshold values for the PT, PSS models, and the activating function vary only with the pulsewidth of the stimulus for a variety of coils at different locations and orientations. Furthermore, the excitation threshold for the PSS model is also independent of axon diameter and best fitted to a simple mathematical function. By comparing the transmembrane potential of the PSS model with the corresponding threshold, the prediction of excitation during magnetic stimulation can be made. Similarly, it is also possible to predict excitation using the PT model and the activating function with the corresponding thresholds provided. By taking advantage of the weighted pulsewidth, this method can even predict the excitation for stimuli with various waveforms, greatly simplifying the determination of neural excitation for magnetic stimulation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Development of speechreading supplements based on automatic speech recognition

    Publication Year: 2000 , Page(s): 487 - 496
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    In manual-cued speech (MCS) a speaker produces hand gestures to resolve ambiguities among speech elements that are often confused by speechreaders. The shape of the hand distinguishes among consonants; the position of the hand relative to the face distinguishes among vowels. Experienced receivers of MCS achieve nearly perfect reception of everyday connected speech. MCS has been taught to very young deaf children and greatly facilitates language learning, communication, and general education. This manuscript describes a system that can produce a form of cued speech automatically in real time and reports on its evaluation by trained receivers of MCS. Cues are derived by a hidden markov models (HMM)-based speaker-dependent phonetic speech recognizer that uses context-dependent phone models and are presented visually by superimposing animated handshapes on the face of the talker. The benefit provided by these cues strongly depends on articulation of hand movements and on precise synchronization of the actions of the hands and the face, Using the system reported here, experienced cue receivers can recognize roughly two-thirds of the keywords in cued low-context sentences correctly, compared to roughly one-third by speechreading alone (SA). The practical significance of these improvements is to support fairly normal rates of reception of conversational speech, a task that is often difficult via SA View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

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.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Bin He
Department of Biomedical Engineering