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Biomedical Engineering, IEEE Transactions on

Issue 8 • Date Aug. 2001

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Displaying Results 1 - 14 of 14
  • Detection of nerve action potentials under low signal-to-noise ratio condition

    Page(s): 845 - 849
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (106 KB) |  | HTML iconHTML  

    Proposes a method for detection of action potentials (APs) under low signal-to-noise ratio conditions. It is based on multiresolution analysis. Three parameters are used for detection. Two of them are for determining if there is an AP or not, and the other is for the estimation of waveforms. The authors' method provides better estimated waveforms than the conventional de-noising approach. View full abstract»

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  • Heart instantaneous frequency (HIF): an alternative approach to extract heart rate variability

    Page(s): 850 - 855
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (290 KB)  

    The authors' study focuses on a new method of estimating the heart rate variability (HRV) which does not require the use of electrocardiogram (ECG) R-wave detection. Contrary to the R-wave detection method which requires a sampling frequency higher than 100 Hz, the one proposed here can be used to calculate the HRV from an ECG signal sampled at a frequency of approximately 5 Hz with a relative mean error of 0.03. This new method is based on extracting the instantaneous fundamental frequency from the EGG. The method could be efficiently used to extract the HRV from an ECG measured for healthy subjects performing an exercise in which the HRV increases linearly with time, and for subjects with respiratory and cardiac problems. The overall error decreased as the authors low-pass filtered the HRV with lower cut-off frequencies. Moreover, it was shown that the method could be efficiently used to calculate the HRV from blood pressure measurements and to be robust to noise. View full abstract»

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  • Bionic wavelet transform: a new time-frequency method based on an auditory model

    Page(s): 856 - 863
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (182 KB) |  | HTML iconHTML  

    A new adaptive wavelet transform, named bionic wavelet transform (BWT), is developed based on a model of the active auditory system. The most distinguishing characteristic of BWT is that its resolution in the time-frequency domain can be adaptively adjusted not only by the signal frequency but also by the signal instantaneous amplitude and its first-order differential. The automatically adjusted resolution, even in a fixed frequency along the time-axis, is achieved by introducing the active control of the auditory system into the wavelet transform (WT). Other properties of BWT include that: 1) BWT is a nonlinear transform that has high sensitivity and frequency selectivity; 2) BWT represents the signal with a concentrated energy distribution; and 3) the inverse BWT can reconstruct the original signal from its time-frequency representation. In order to compare these three properties between BWT and WT, experiments were conducted on both constructed signals and real speech signals. The results show that BWT performs better than WT in these three aspects, and that BWT is appropriate for speech signal processing, especially for cochlear implants. View full abstract»

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  • Analytical solution for pulsatile axial flow velocity waveforms in curved elastic tubes

    Page(s): 864 - 873
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (219 KB) |  | HTML iconHTML  

    An analytical solution for pulsatile axial flow velocity waveforms in curved elastic tubes is presented. The result is obtained by exact solution of linearized Navier-Stokes and tube motion equations in a toroidal coordinate system. Fourier analysis is used to divide the flow into constant and oscillatory components which are separately considered. The solution is used to investigate the effects of curvature on volumetric axial velocity flow waveforms, as would be measured by Doppler ultrasound techniques. In typical human arteries, the greatest effects of curvature on the volumetric axial flow are exerted on the constant component and at low values of the frequency parameter for the oscillatory components. Here, the magnitude and phase angle of oscillatory flow in the curved tube, relative to that in the straight tube, differ by maximum values of 1.2% and 0.15 rad, respectively. However, constant flow may vary by as much as 60% at high Dean numbers. The solution is presented in a form similar to Womersley's solution for the straight elastic tube and may, thus, be incorporated into a transmission-line analog model. These models are frequently used to investigate axial flow velocity variations in mammalian circulatory systems and this work offers a tool which may extend these models to incorporate the effects of curvature. View full abstract»

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  • Modeling and closed-loop control of hypnosis by means of bispectral index (BIS) with isoflurane

    Page(s): 874 - 889
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (301 KB) |  | HTML iconHTML  

    A model-based closed-loop control system is presented to regulate hypnosis with the volatile anesthetic isoflurane. Hypnosis is assessed by means of the bispectral index (BIS), a processed parameter derived from the electroencephalogram. Isoflurane is administered through a closed-circuit respiratory system. The model for control was identified on a population of 20 healthy volunteers. It consists of three parts: a model for the respiratory system, a pharmacokinetic model and a pharmacodynamic model to predict BIS at the effect compartment. A cascaded internal model controller is employed. The master controller compares the actual BIS and the reference value set by the anesthesiologist and provides expired isoflurane concentration references to the slave controller. The slave controller maneuvers the fresh gas anesthetic concentration entering the respiratory system. The controller is designed to adapt to different respiratory conditions. Anti-windup measures protect against performance degradation in the event of saturation of the input signal. Fault detection schemes in the controller cope with BIS and expired concentration measurement artifacts. The results of clinical studies on humans are presented. View full abstract»

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  • The biocompatibility, integrity, and positional stability of an injectable microstimulator for reanimation of the paralyzed larynx

    Page(s): 890 - 897
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (141 KB) |  | HTML iconHTML  

    The biocompatibility, integrity, positional stability, and potential use of hermetically sealed injectable wireless micromachined microstimulators were investigated for reanimation of the paralyzed larynx. The device, consisting of silicon and glass, has been tested and proven to be biocompatible with no evidence of pathological tissue reaction or rejection up to one-year implantation in the rat dorsum and canine larynx. By one month, each unit was encapsulated by a thin membrane, which thickened to form a fibrous layer of less than 500 μm at 6-12 months. The microstimulators demonstrated long-term in vivo durability: the hermetic seal of only one in ten devices was breached. Once implanted, migration of the device varied from 0 to 3 cm, depending upon the extent of surgical dissection. No discernable migration was noted when the tissue dissection was minimal. Studies utilizing a modified device equipped with electrodes indicated that migration was nominal with sufficient positional stability to ensure activation of target muscles for glottis opening. This study supported the feasibility of using a microstimulator for reanimation of paralyzed laryngeal muscles that open the airway during breathing. This innovative approach to treatment would alleviate the need for a tracheotomy or surgical resection of the vocal fold. View full abstract»

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  • Calibrated single-plunge bipolar electrode array for mapping myocardial vector fields in three dimensions during high-voltage transthoracic defibrillation

    Page(s): 898 - 910
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (189 KB) |  | HTML iconHTML  

    Mapping of the myocardial scalar electric potential during defibrillation is normally performed with unipolar electrodes connected to voltage dividers and a global potential reference. Unfortunately, vector potential gradients that are calculated from these data tend to exhibit a high sensitivity to measurement errors. This paper presents a calibrated single-plunge bipolar electrode array (EA) that avoids the error sensitivity of unipolar electrodes. The EA is triaxial, uses a local potential reference, and simultaneously measures all 3 components of the myocardial electric field vector. An electrode spacing of approximately 500 μm allows the EA to be direct-coupled to high-input-impedance, isolated, differential amplifiers and eliminates the need for voltage dividers. Calibration is performed with an electrolytic tank in which an accurately measured, uniform electric field is produced. For each EA, unique calibration matrices are determined which transform potential difference readings from the EA to orthogonal components of the electric field vector. Elements of the matrices are evaluated by least squares multiple regression analysis of data recorded during rotation of the electric field. The design of the electrolytic tank and electrode holder allows the electric field vector to be rotated globally with respect to the electrode axes. The calibration technique corrects for both field perturbation by the plunge electrode body and deviations from orthogonality of the electrode axes. A unique feature of this technique is that it eliminates the need for mechanical measurement of the electrode spacing. During calibration, only angular settings and voltages are recorded. For this study, ten EAs were calibrated and their root-mean-square (rms) errors evaluated. The mean of the vector magnitude rms errors over the set of 10 EAs was 0.40% and the standard deviation 0.07%. Calibrated EAs were also tested for multisite mapping in 4 dogs during high-voltage transthorac- - ic shocks. View full abstract»

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  • Single-unit neural recording with active microelectrode arrays

    Page(s): 911 - 920
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (221 KB) |  | HTML iconHTML  

    Discusses the single-unit recording characteristics of microelectrode arrays containing on-chip signal processing circuitry. Probes buffered using on-chip unity-gain operational amplifiers provide an output resistance of 200 Ω with an input-referred noise of 11-μV root-mean-square (rms) (100 Hz-10 kHz). Simultaneous in vivo recordings from single neurons using buffered and unbuffered (passive) iridium recording sites separated by less than 20 μm have shown that the use of on-chip circuitry does not significantly degrade system noise. Single-unit neural activity has also been studied using probes containing closed-loop preamplifiers having a voltage gain of 40 dB and a bandwidth of 13 kHz, and several input de-baseline stabilization techniques have been evaluated. Low-noise in vivo recordings with a multiplexed probe have been demonstrated for the first time using an external asymmetrical clock running at 200 kHz. The multiplexed system adds less than 8-μV rms of noise to the recorded signals, suppressing the 5-V clock transitions to less than 2 ppm. View full abstract»

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  • Dielectrophoretic trapping of dissociated fetal cortical rat neurons

    Page(s): 921 - 930
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (581 KB) |  | HTML iconHTML  

    Recording and stimulating neuronal activity at multiple sites can be realized with planar microelectrode arrays. Efficient use of such arrays requires each site to be covered by at least one neuron. By application of dielectrophoresis (DEP), neurons can be trapped onto these sites. This study investigates negative dielectrophoretic trapping of fetal cortical rat neurons. A planar quadrupole microelectrode structure was used for the creation of a nonuniform electric field. The field was varied in amplitude (1, 3, and 5 V) and frequency (10 kHz-50 MHz). Experimental results were compared with a theoretical model to investigate the yield (the number of neurons trapped in the center of the electrode structure) with respect to time, amplitude and frequency of the field. The yield was a function of time 13/ according to theory. However, unlike the model predicted, an amplitude-dependent frequency behavior was present and unexpected peaks occurred in the DEP-spectra above 1 MHz. Gain/phase measurements showed a rather unpredictable behavior of the electrode plate above 1 MHz, and temperature measurement showed that heating of the medium influenced the trapping effect, especially for larger amplitudes and higher frequencies. View full abstract»

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  • A novel method for beat-to-beat detection of ventricular late potentials

    Page(s): 931 - 935
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    A novel method for beat-to-beat detection of ventricular late potentials (VLP) from high-resolution electrocardiograms (ECGs) is presented. ECG signals from the X lead are first filtered using a bandpass filter, and then a time-sequence adaptive filter, to improve its signal-to-noise ratio. Eight features are extracted using the wavelet transform, from the VLP time-frequency distribution of the filtered ECG signals, and used as inputs of specially designed artificial neural network for VLP recognition. The artificial neural network was trained and tested using clinical data, respectively. The results show that the presented method can detect beat-to-beat-based VLP with sensitivity of 80% and specificity of 77%, and the detection accuracy is 78%. View full abstract»

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  • Time-frequency analysis of temporomandibular joint (TMJ) clicking sounds using radially Gaussian kernels

    Page(s): 936 - 939
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (76 KB) |  | HTML iconHTML  

    Temporomandibular joint (TMJ) sounds and motion were recorded during two clinically-derived movements-simple jaw opening and jaw protrusion followed by opening-from ten patients. A new time-frequency method-radially Gaussian kernel distribution-was applied to classify the TMJ clicking sounds into six groups, type I to type VI, based on the time-frequency patterns of energy distribution. The number of clicks and percentage of each type were examined. Relations between the two movements were examined by the prevalence of each type. A detailed classification of TMJ clicking sounds is provided by time-frequency patterns and may provide a better understanding of temporomandibular disorders. View full abstract»

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  • Atrial activity enhancement by Wiener filtering using an artificial neural network

    Page(s): 940 - 944
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB) |  | HTML iconHTML  

    Describes a novel technique for the cancellation of the ventricular activity for applications such as P-wave or atrial fibrillation detection. The procedure was thoroughly tested and compared with a previously published method, using quantitative measures of performance. The novel approach estimates, by means of a dynamic time delay neural network (TDNN), a time-varying, nonlinear transfer function between two ECG leads. Best results were obtained using an Elman TDNN with 9 input samples and 20 neurons, employing a sigmoidal tangencial activation in the hidden layer and one linear neuron in the output stage. The method does not require a previous stage of QRS detection. The technique was quantitatively evaluated using the MIT-BIH arrhythmia database and compared with an adaptive cancellation scheme proposed in the literature. Results show the advantages of the proposed approach, and its robustness during noisy episodes and QRS morphology variations. View full abstract»

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  • Comments on "Femoral surface strain in intact composite femurs: A custom computer analysis of the photoelastic coating technique" [with reply]

    Page(s): 944 - 946
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (29 KB)  

    Cristofolini and Viceconti read with great interest the title paper by Grecula et al. (see ibid., vol. 47, p. 926-33, 2000). Cristofolini and Viceconti were pleased to see an increasing interest toward new tools to improve in vitro investigations in orthopedics. In fact there still a strong need to improve the way hip prostheses are tested. The work Grecula et al. presented definitely gives a positive contribution in this direction, since they developed a new approach to assess the state of strains in the femur. In fact Grecula et al. proposed to use a novel indicator, the average strain areas, rather than looking at local information only. However, Cristofolini and Viceconti feel that Grecula et al. might have overlooked some methodological details that can possibly undermine the validity of the actual results they present, introducing both a significant bias, and a large scatter of the results. In reply Grecula et al. say that the goal of the project reported in the original paper was to improve on the methods available for measuring the surface strains in the proximal femur. Visualizing the complete topography of surface strains with the photoelastic coating technique is appealing but frustrating due to limits in its quantitative utility. Grecula et al. incorporated the advantages of computer imaging and software interpretation to improve the quantitative results of this technique. As with any new technique, Grecula et al. designed the protocol to be as simple as possible to reduce possible errors and variability. While the loading configuration was not necessarily physiologic and possibly over-constrained, it did allow the repeatable load transfer through the femur that was necessary for validating the computer techniques that Grecula et al. were testing. View full abstract»

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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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