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Biomedical Engineering, IEEE Transactions on

Issue 8 • Date Aug. 1992

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Displaying Results 1 - 13 of 13
  • Multiple-model adaptive predictive control of mean arterial pressure and cardiac output

    Page(s): 765 - 778
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1159 KB)  

    A multiple-model adaptive predictive controller has been designed to simultaneously regulate mean arterial pressure and cardiac output in congestive heart failure subjects by adjusting the infusion rates of nitroprusside and dopamine. The algorithm is based on the multiple-model adaptive controller and utilizes model predictive controllers to provide reliable control in each model subspace. A total of 36 linear small-signal models were needed to span the entire space of anticipated responses. To reduce computation time, only the six models with the highest probabilities were used in the control calculations. The controller was evaluated on laboratory animals that were either surgically or pharmacologically altered to exhibit symptoms of congestive heart failure. During trials, the controller performance was robust with respect to excessive switching between models and nonconvergence to a single dominant model. A comparison with a previous multiple-drug controller design is made. View full abstract»

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  • Blood glucose response to stress hormone exposure in healthy man and insulin dependent diabetic patients: prediction by computer modeling

    Page(s): 779 - 790
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1030 KB)  

    To establish a qualitative and quantitative model of blood glucose response to stress hormone exposure, healthy subjects (HS) on and off somatostatin (250 mu gf/h) and insulin-dependent diabetic patients were infused with either epinephrine, glucagon, cortisol, growth hormone, or a cocktail of these hormones, raising plasma stress hormones to values seen in severe diabetic ketoacidosis. The developed input/output model consists of two submodels interconnected in series plus two additional submodels for correction of gains describing both sensitivity of tissue response and utilization as well as provision of glucose. It was shown and confirmed experimentally that blood glucose response to stress hormones was essentially nonlinear. Furthermore, the mathematical models for healthy subjects and for insulin-dependent diabetic patients proved to be of the same structure, differing only in the values of some typical parameters. View full abstract»

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  • A random dipole model for spontaneous brain activity

    Page(s): 791 - 804
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    The statistical properties of the EEG and the MEG can be described mathematically as the result of randomly distributed dipoles representing the interactions of cortical neurons. If the dipoles are in a spherical volume conductor and have no preference for any direction, the variance of a differentially measured EEG signal is only a function of the electrode distance. The theoretically derived variance function is compared with EEG and MEG measurements. It is shown that a dipole with a fixed position and a randomly fluctuating amplitude is an adequate model for the alpha -rhythm. An expression for the covariance between the magnetic field and a differentially measured EEG signal is derived. This covariance is considered as a function of the magnetometer position. The theory can be used to obtain a (spatial) covariance matrix of the background noise, which occurs in evoked potential measurements. Such a covariance matrix can be used to obtain a maximum likelihood estimator (MLE) of the dipole parameters in evoked potential studies. View full abstract»

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  • Equivalent source estimation based on the calculation of the electric field from depth EEG data

    Page(s): 805 - 817
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    A method for the estimation of equivalent source position and strength based on the estimation of the electric field from depth electroencephalographic (EEG) data is described. The calculation method for the electric field is based on a tetrahedral geometry. The proposed approach for source parametrization is twofold. Firstly, the distribution of electrical energy by the squared norm of the electric field vector can give an estimate of the source position, without having to assume a dipole source. Secondly, the average electric field can be related to the dipole magnitude and orientation of the equivalent source. Simulation results demonstrated the potential usefulness of the method. The effects of noise and sampling, and the geometry of the measurement system (i.e. implanted electrodes) relative to the source were also investigated through simulations. View full abstract»

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  • Detection of reentry currents in atrial flutter by magnetocardiography

    Page(s): 818 - 824
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    The magnetic signal produced by atrial flutter induced in isolated rabbit hearts has been detected. A simple model describing a circus reentry path is discussed and fitted to the experimental data. Agreement between the simulated magnetic field obtained using the model and animal experimental results suggests that, at least in the preparation used, the presence of a reentry current can be checked and described in a zero-order approximation by the circular motion of a constant-intensity current dipole. It appears that magnetocardiography can be used as a noninvasive technique to locate and to provide information about the radius of the circuit of such reentry currents.<> View full abstract»

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  • Direct computation of ultrasound phased-array driving signals from a specified temperature distribution for hyperthermia

    Page(s): 825 - 835
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    A method that obtains ultrasound hyperthermia applicator phased-array element driving signals from a desired temperature distribution is presented. The approach combines a technique which computes array element driving signals from focal point locations and intensities with a technique which calculates focal point locations and power deposition values from temperature requirements. Temperature specifications appear as upper and lower bounds within the tumor volume, and a focal point placement algorithm chooses focal patterns capable of achieving the temperature range objective. The linear algebraic structure of the method allows rapid calculation of both the phased-array driving signals and an approximate temperature field response. Computer simulations verify the method with a spherical section array (SSA) for a variety of temperature specifications and blood perfusion values. The scheme applies to any phased-array geometry. View full abstract»

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  • Thermal model for the local microwave hyperthermia treatment of benign prostatic hyperplasia

    Page(s): 836 - 844
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    A system for the noninvasive localized, hyperthermia treatment of benign prostatic hyperplasia was investigated. The system uses a microwave transrectal antenna with a water cooled jacket to achieve localized hyperthermia. The purpose of this study is to model the temperature rise in the prostate and in the surrounding tissue during treatment. The specific absorption rate distribution for the transrectal probe is measured in a muscle tissue equivalent phantom. The specific absorption rate information is used with a finite-element solution of the bioheat transfer equation to give the temperature rise during the treatment. The finite-element solution is further used to determine the effect of the microwave power, the cooling fluid temperature, and the blood perfusion on the tissue temperature rise. The results of the solution are compared to temperature measurements in a canine protocol. It was found that the maximum temperature rise in the tissue during treatment is 44 degrees C at a depth of 2 cm from the rectal mucosa. View full abstract»

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  • Direct use of CT scans for hyperthermia treatment planning

    Page(s): 845 - 851
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (617 KB)  

    In the field of deep regional hyperthermia cancer therapy, patient-specific, three-dimensional computer modeling for treatment planning in the BSD-2000 hyperthermia system is addressed. Two persistent problems have been the large amount of time needed to create the patient model from a computed tomography (CT) scan (one and a half days), and the lack of a way to view the large amounts of data that comprise the output of a treatment plan, i.e. the specific absorption rate (SAR) at 20000 to 30000 cells. A method that obtains the dielectric properties needed for hyperthermia treatment planning directly from the CT image with minimum operator interaction is presented. Comparison is made with the previous method of drawing contours around the different tissue types. A method which displays the output as iso-SAR contours directly over the CT scan of the patient is described. View full abstract»

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  • Distinguishability in impedance imaging

    Page(s): 852 - 860
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (725 KB)  

    Impedance imaging systems apply currents to the surface of a body, measure the induced voltages on the surface, and from this information reconstruct an approximation to the electrical conductivity in the interior. A detailed discussion of several ways to measure the ability of such a system to distinguish between two different conductivity distributions is given. The subtle differences between these related measures are discussed, and examples are provided to show that these different measures can give rise to different answers to various practical questions about system design. View full abstract»

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  • Comparison of algorithms for tracking short-term changes in arterial circulation parameters

    Page(s): 861 - 867
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (598 KB)  

    Three recursive methods especially suited for identification of systems with rapidly changing parameters are applied to tracking of the viscoelastic properties of the systemic arterial bed. These methods include two least squares (LS) algorithms with constant or variable forgetting factor (RLS and LSVF) and an LS algorithm incorporating both a constant forgetting factor and covariance modification (CFCM). The methods are presented in a unified framework, and their sensitivity with respect to the design variables is investigated using noisy data from computer simulations. All analyzed methods have satisfactorily tracked rapid changes in peripheral resistance. The LSVF method, which offers slightly better performances than the classical RLS, may be preferred when calculation efficiency is the prime requirement. The CFCM algorithm, although maintaining reasonable simplicity, shows the best tracking ability also on varying of the noise sequence. View full abstract»

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  • On detecting the presence of fetal R-wave using the moving averaged magnitude difference algorithm

    Page(s): 868 - 871
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (326 KB)  

    An efficient algorithm for detecting the presence of a fetal QRS complex is presented. The proposed fetal QRS detection method computes the averaged magnitude of the difference between the fetal ECG signal and the reference signal to detect the fetal QRS event. The detected signal fetal QRS complexes are exponentially averaged to generate the template signal which can track the slowly varying shape of the fetal ECG signal. As an effort to obtain improved detection performances, two approaches of normalizing the fetal ECG signal and the template are considered. View full abstract»

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  • Muscle input-output model: the static dependence of force on length, recruitment, and firing period

    Page(s): 871 - 874
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (379 KB)  

    Steady-state isometric active muscle force has a bilinear dependence on length and firing period (inverse of firing rate). At a fixed length, force increases linearly with decreasing firing period. The slope decreases linearly with increasing muscle length, and the value of force extrapolated to zero firing period remains constant. This relationship can be used in Hill-type muscle models. View full abstract»

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  • Comments, with reply, on "Some imaging parameters of the oblique dipole layer cardiac generator derivable from body surface electrical potentials" by F. Greensite

    Page(s): 874 - 875
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (223 KB)  

    The commenters maintain that the above-titled paper (ibid., vol.39, p.159-64, 1992) contains a flawed derivation of the heart surface source model for the anisotropic case, and that the argument that there will be a particular discontinuity in the body surface electrocardiographic waveform is based on a questionable picture of the time course of the area of breakthrough. The author responds that there is a flow in the commenters' argument that is one of the consequences of his work, and he elaborates on the matter.<> 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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Meet Our Editors

Editor-in-Chief
Bin He
Department of Biomedical Engineering