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Biomedical Engineering, IEEE Transactions on

Issue 3 • Date March 1993

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Displaying Results 1 - 12 of 12
  • Orthonormal (Fourier and Walsh) models of time-varying evoked potentials in neurological injury

    Page(s): 213 - 221
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (835 KB)  

    The hypothesis that injury-related changes in evoked potential (EP) signals can be modeled by orthonormal basis functions is tested. Two models of time-varying EP signals are evaluated: the Fourier series model (FSM) and the Walsh function model (WFM). The Fourier and Walsh coefficients are estimated with the aid of an adaptive least-mean-squares (LMS) technique. Results from computer simulations illustrate how selection of model order and of the adaptation rate of the estimator affect the signal-to-noise ratio (SNR). The FSM results in a somewhat higher steady-state SNR than does the WFM; however, the WFM is less computationally complex than is the FSM. These two orthonormal functions are used to evaluate transient response to hypoxic hypoxia in anesthetized cats. Trends of the first five frequencies (Fourier) and sequencies (Walsh) show that the lower frequencies and sequencies may be sensitive indicators of hypoxic neurological injury. View full abstract»

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  • A method of analyzing nonstationary ionic channel current fluctuations in the presence of an additive measurement noise

    Page(s): 222 - 229
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (551 KB)  

    A method for estimating the parameters of nonstationary ionic channel current fluctuations (NST-ICFs) in the presence of additive measurement noise is proposed. The case in which the sample records of corrupted NST-ICTs are available for estimation, and the experiment can be repeated many times to calculate the statistics of noisy NST-ICFs, is considered. The conventional second-order regression model expressed in terms of the mean and variance of noisy NST-ICFs is derived theoretically, assuming that NST-ICFs are binomially distributed. The parameters of NST-ICFs that are of interest can be estimated without interference from the additive measurement noise by identifying the regression coefficients. The accuracy of the parameter estimates is theoretically evaluated using the error-covariance matrix of the regression coefficients. The validity and effectiveness of the proposed method are demonstrated in a Monte Carlo simulation of Na + channels kinetics. View full abstract»

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  • Diagnostica-a Bayesian decision-aid system-applied to hypertension diagnosis

    Page(s): 230 - 236
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (549 KB)  

    Diagnostica is a Bayesian statistical tool designed to collect and store the patient's data, suggest a diagnosis, and explain the decision in terms of density distributions. The program is written in C language on MacIntosh support. It is describes using a case study of differential diagnosis between essential and secondary hypertensions. Seventeen experimental parameters were taken into consideration, all of them available during the first medical examination. The density distributions of all items were established from the ARTEMIS experimental database. Both a priori probabilities of different types of hypertension and loss coefficients are taken into account in the calculations. Diagnostica can be used in a 'make diagnosis' mode or in an 'edition' mode. In the first case it can serve a physician in everyday practice; in the second it becomes a tool for medical research. View full abstract»

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  • Lumped-parameter model for in vivo cochlear stimulation

    Page(s): 237 - 245
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (792 KB)  

    A lumped-parameter model that simulates the in vivo electrical properties of a guinea pig cochlea implanted with a multielectrode stimulating array is presented. A basic model of the low-frequency electroanatomy in a normally functioning guinea pig cochlea is developed by adding critical membrane capacitances to D. Strelioff's resistive network model (1973). The basic model of normal cochlear tissues is modified to account for anatomical and physiological differences between a normal and implanted cochlea, resulting in an impedance model of an implanted cochlea. Simulating the results of in vivo cochlear stimulation verifies the accuracy with which the modified cochlear model represents electrical properties within an electrically stimulated cochlea. Generalized simulations using this model suggest a straightforward phasing scheme capable of achieving sharply focused, channel-independent multielectrode cochlear stimulation. View full abstract»

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  • Effect of paddle placement and size on defibrillation current distribution: a three-dimensional finite element model

    Page(s): 246 - 255
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    A realistic three-dimensional finite-element model (FEM) of the conductive anatomy of a canine thorax was constructed for use in the study of transthoracic electrical defibrillation. The model was constructed from a series of 21 cross-sectional computed tomography (CT) scans of a 14.5 kg beagle, each separated by 0.82 cm. The electrical conductive properties of eight distinct tissues were incorporated, including the anisotropic properties of skeletal muscle. Current density distributions were obtained for six paddle pairings and two paddle sizes. A quantitative basis for comparing the resulting distributions was formulated. The results suggest that placing one or both of the paddles near the heart delivers a higher fraction of current to the heart. However, such placements also produce a less uniform myocardial current density distribution and thus have a higher potential for causing damage. Some paddle positions produced myocardial current densities close to the threshold for damage in successful defibrillations. The results indicate that 12 cm paddles may offer modest advantages over 8 cm paddles in clinical defibrillation. View full abstract»

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  • Estimating the 95% effective defibrillation dose

    Page(s): 256 - 265
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (975 KB)  

    Minimum-squared-error (MinSE) testing protocols and a MinSE estimator that accurately estimate the voltage that defibrillates 95% of the time (the ED95) are presented. The MinSE experimental procedures, presented in the form of lookup tables, detail the response to successful and unsuccessful trials. The lookup tables also show the ED95 estimates calculated from the observed results using the MinSE estimator. The MinSE estimator and experimental procedure were evaluated in a study of five dogs (19-25 kg, heart weights 139.3-236.9 gm) using nonthoracotomy implantable defibrillator electrodes and a biphasic defibrillation waveform (3.5 ms first phase, 2.0 ms second phase). For ED95 between 0.0 and 800.0 V, the measured RMS error was 15% of the mean measured ED95 for the MinSE, four-test-shock, ED95 estimates. If the protocols are designed with an ED95 population distribution assumption for animals of the same species and size, and defibrillation is constrained to one electrode configuration and waveform, the estimates improve by 3.8%. The MinSE approach can be extended to a variety of defibrillation parameter estimation problems. View full abstract»

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  • Real-time cardiac output estimation of the circulatory system under left ventricular assistance

    Page(s): 266 - 275
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (753 KB)  

    A method for indirect and real-time estimation of the cardiac output of the circulatory system supported by the left ventricular assist device (LVAD) is proposed. This method has low invasiveness and is useful for clinical applications of the LVAD since it needs only two measurements: the rate of blood outflow from the LVAD and the aortic pressure. The method is based on a system identification technique for the time-series model of the cardiovascular system and requires less computational time than other methods with similar estimation accuracy. Hence, the method could be implemented in a personal computer system and realize online, real-time estimation of the instantaneous outflow rate of the natural heart. Results obtained in vitro using a mock circulatory system and in vivo using an adult goat show that the method can yield a fairly high correlation coefficient between the true stroke volume of the natural heart and its estimate of more than 0.99 (in vitro) or 0.95 (in vivo). The estimation method thus appears suitable for clinical use. View full abstract»

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  • Portable system for quantifying motor abnormalities in Parkinson's disease

    Page(s): 276 - 283
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    To quantify motor disabilities in Parkinson's disease (PD), a compact, portable neurophysiological system based on a personal computer was designed to measure tremor, bradykinesia, and muscle tone. Tremor was detected by solid-state accelerometers and translated into a digital signal. The system displayed the root-mean-square (RMS) displacements and frequency distribution of the tremor in the horizontal and vertical planes, along with a reconstructed graphic image of the displacement. Bradykinesia was measured using a panel that detects release and depression of switches in response to auditory and visual signals; the system calculated subjects' reaction times and movement times in milliseconds. Tone at the elbow was measured by strapping the upper extremity to a lightweight low-friction cradle and then passively moving the cradle with an instrumented handle. Signals representing torque and arm angle were processed by the computer and displayed in real time on the screen with stiffness as a mean slope in Nm/degree. Clinical tests indicate that this system provides a convenient and accurate method for quantifying important aspects of the Parkinsonian syndrome and might be applicable to other movement disorders. View full abstract»

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  • Venous occlusion plethysmography using a fiber-optic sensor

    Page(s): 284 - 289
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    The results of comparative testing of a fiber-optic sensor used as an alternative method for limb blood flow assessment by venous occlusion plethysmography are presented. The measurement of volume changes following venous occlusion was performed with a variety of methods, including the commonly used mercury strain-gauge, which suffers temperature drift and long-term instability as well as environmental problems (the marketing of mercury sensors is prohibited, beginning in 1993). The evaluation and optimization of the fiber optic microbending sensor is described in detail, along with results of the comparison with the mercury sensor for lower limb blood flow measurements. View full abstract»

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  • A laser Doppler instrument for in vivo measurements of blood flow in single renal arterioles

    Page(s): 290 - 297
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    A laser Doppler instrument has been developed to measure the blood flow in single vessels for the study of the dynamics of local control mechanisms. A commercial blood perfusion monitor, designed to measure blood perfusion in a vascular field containing many randomly oriented blood vessels, was modified to measure blood flow in a single arteriole. In vitro tests of the instrument revealed that the relationship between blood flow and Doppler shift was not a simple linear function. Causes of nonlinearity are revealed, and it is shown that proper use of the device avoids the problem. The device was applied to efferent arterioles that are visible on the surface of the rat kidney, and changes in the kidney blood flow were induced and measured. An oscillation in the tubular pressure at 0.035 Hz, that was previously described and attributed to a local feedback mechanism, was found in the arteriolar blood flow. The instrument is easy to use and provides temporal resolution. View full abstract»

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  • Development of a dual function sensor system for measuring pressure and temperature at the tip of a single optical fiber

    Page(s): 298 - 302
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    A dual function sensor system has been developed for measuring pressure and temperature at the tip of a single optical fiber. The sensor contains three parts: a filter band-edge shift temperature sensor, a short-wavelength-reflecting dichroic filter, and a diaphragm-based spectral modulation pressure sensor. The sensor system uses a separate and distinct light-emitting diode (LED) for interrogating each sensor, three 100/140 mm step-index fused couplers for managing light, and separate paired photodiode assemblies for analyzing the return light signal from each sensor. In bench tests, each sensor performed to specification and there was no crosstalk between sensors. This sensor design has potential catheter applications where catheter size must be kept to an absolute minimum. View full abstract»

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  • Patient isolation in multichannel bioelectric recordings by digital transmission through a single optical fiber

    Page(s): 302 - 308
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (609 KB)  

    A design for patient isolation in 64-channel electrocardiogram (ECG) recordings is presented. Small dimensions of the isolated section and the use of an optical fiber as the only connection between the isolated section and the grounded section of the measurement system ensured a minimal capacitance between the patient and the environment. The consistent low-power design of the isolated section resulted in a power consumption of 210 mW, which allowed a 10 h continuous operating time of the battery-powered isolated section. The system handles 64 signals with a dynamic range of 75 dB. Analog-to-digital conversion is performed in the isolated section with a sample rate of 1 kHz/channel. The receiver interfaces to a commercially available DMA board for a standard personal computer. 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