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Biomedical Engineering, IEEE Transactions on

Issue 12 • Date Dec. 1991

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Displaying Results 1 - 13 of 13
  • Null-balance transducer for isometric force measurements and length control of single heart cells

    Page(s): 1165 - 1174
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    An ultrasensitive, optical-fiber-based force transducer was developed to measure the microscopic force of contraction of single heart cells. The original design permits approximately 1% shortening of cell length to occur during twitch contractions. It is shown that the shortening can be reduced significantly by adding a piezoelectric bimorph actuator and closed-loop control. As a result, the effective stiffness of the transducer can be increased by a factor of about 100, and cell shortening reduced to approximately 0.01%. For the force probes typically used, this is equivalent to a movement of less than 20 nm for a typical value of 100 nN peak cell force in single frog ventricular cells. The gain in stiffness is obtained without sacrificing sensitivity, although at the expense of frequency response. The design permits control of cell length and is applicable to studies of the mechanical stiffness of cardiac cells. View full abstract»

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  • A system to acquire and record physiological and behavioral data remotely from nonhuman primates

    Page(s): 1175 - 1185
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    An integrated system to record physiological and behavioral variables from nonhuman primates in social groups is described. The system records data simultaneously from two animals in family groups of five. It synchronizes behavioral and physiological data within 16 ms, either online or from recordings. Behavioral data are entered by trained observers online or from videotape. Recordings of physiological data are produced online as stripchart records, tape recordings on the audio channels of video cassettes, and magnetic disk files. The physiological data include two arterial blood flows, arterial blood pressure, and heart rate. The data are transmitted from freely behaving animals to a central site via radio telemetry. The infrared link controls the radio transmitter and physiological signal-processing electronics, as well as two sources of drugs for each animal. All of the electronics are contained in a small, light backpack that can be worn by either male or female baboons. View full abstract»

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  • Lower extremity angle measurement with accelerometers-error and sensitivity analysis

    Page(s): 1186 - 1193
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    The use of accelerometers for angle assessment of the lower extremities is investigated. This method is evaluated by an error-and-sensitivity analysis using healthy subject data. Of three potential error sources (the reference system, the accelerometers, and the model assumptions) the last is found to be the most important. Model calculations based on data obtained by the Elite video motion analysis system showed the rigid-body assumption error to be dominant for high frequencies (>10 Hz), with vibrations in the order of 1 mm resulting in errors of one radial or more. For low frequencies (<5 Hz), the imperfect fixation of the accelerometers combined with a nonhinge-type knee joint gave an error contribution of +or-0.03 rad. The walking pattern was assumed to be two-dimensional, which was shown to result in an error of +or-0.04 rad. Accelerations due to rotations of the segments could be neglected. The total error computed for low frequencies (+or-0.07 rad) is comparable to the experimental difference between the current and the reference system. View full abstract»

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  • Simple photon diffusion analysis of the effects of multiple scattering on pulse oximetry

    Page(s): 1194 - 1203
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    Photon diffusion theory is used to derive analytical expressions that relate the AC-DC intensity ratios measured by transmission-mode and reflectance-mode pulse oximeters to arterial oxygen saturation (S aO 2). The effects of multiple scattering are examined by comparing the results of the photon diffusion analysis with those obtained using an analysis is based on the Beer-Lambert law which neglects scattering. It is shown that the difference between the average lengths of the paths traveled by red and infrared photons makes the calibration curve of oximeters sensitive to the total attenuation coefficients of the tissue in the two wavelength bands, as well as to absorption by the pulsating arterial blood. Therefore, the shape of the calibration curve is affected by tissue blood volume, source-detector placement, and other variables that change the wavelength dependence of the attenuation coefficient of the tissue. After evaluating the relationship between S aO 2 and the red/IR AC-DC ratio under a variety of physiological conditions, it is concluded that for oximeters utilizing fixed calibration curves based on measurements obtained from normal subjects, errors introduced by interfering variables should be less than a few percent when S aO 2 exceeds 70%. View full abstract»

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  • Left-ventricular dynamic model based on constant ejection flow periods

    Page(s): 1204 - 1212
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    A simulation model that is based on findings of constant ejection flow experiments is presented. This model is tested on measured pressure and volume data. The results show that when the model is fitted on one single beat, left ventricular pressure can satisfactorily be described by a three-element model without deactivation. When isovolumic pressure has to be described by the model as well, introduction of deactivation is necessary. The quality of the model was further tested by fitting it to two beats with different ejection parameters. Deactivation again was necessary for a good fit. Only with a deactivation effect in the model, the component values found are close to the normal range found with constant-flow-period experiments in the rabbit left ventricles. From the simulation results it is concluded that (at least for constant ejection flow periods) elastance, resistance, series-elastance, and deactivation effects all are necessary in describing (and predicting) left ventricular pressure. View full abstract»

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  • Feedback control methods for task regulation by electrical stimulation of muscles

    Page(s): 1213 - 1223
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    Three feedback control algorithms of varying complexity were compared for controlling three different tasks during electrical stimulation of muscles. Two controllers use stimulus pulse width (PW) (or recruitment) modulation to grade muscle force (the fixed-parameter, first-order PW controller and the adaptive controller). The third controller varies both stimulus pulse (SP) width and period simultaneously for muscle force modulation (the PW/SP controller). The three tasks tested were isometric torque control, unloaded position tracking, and control of transitions between isometric and unloaded conditions. The comparative evaluation was carried out in an intact cat ankle joint with stimulation of tibialis anterior and medial gastrocnemius muscles. The simplest PW controller demonstrated robust control for all tasks. The PW/SP controller improved the performance of the PW controller significantly for control of isometric torque and load transition, but only slightly for control of unloaded joint position. However, the adaptive controller did not consistently achieve a significant improvement in performance compared with the PW controller for any task. View full abstract»

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  • Feedback control of electrically stimulated muscle using simultaneous pulse width and stimulus period modulation

    Page(s): 1224 - 1234
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    The closed-loop control of electrically stimulated muscle using simultaneous pulse width and frequency modulation is considered. It is shown how the addition of pulse frequency modulation to pulse width modulation can improve controller performance. In single muscle operation, the combination of pulse width and stimulus pulse frequency modulation results in better control of transient responses than with pulse width modulation alone. In the case of costimulation, the controller modulates the pulse stimulus periods of the antagonists in a reciprocal manner, to ensure stable and fast responses. This feedback controller was evaluated in animal experiments. Step responses with rapid rise times but without overshoot were obtained by the combined modulation. Good steady-state and transient performance were obtained over a wide range of static lengths and commands, under different loading conditions and in different animals. View full abstract»

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  • A comparison of static and dynamic characteristics between rectus eye muscle and linear muscle model predictions

    Page(s): 1235 - 1245
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    The muscle is modeled as a viscoelastic parallel combination connected to a parallel combination of active state tension generator, viscosity element, and length tension elastic element. Each of the elements is linear and their existence is supported with physiological evidence. The static and dynamic properties of the muscle model are compared to rectus eye muscle data. The length-tension characteristics of the model are in good agreement with the data within the operating region of the muscle. With the muscle model incorporated into a lever system to match the isotonic experiment paradigm, simulation results for this linear system yield a nonlinear force-velocity curve. Moreover, the family of force-velocity curves generated with different stimulus rates reported in the literature match the predictions of the model without parametric changes. View full abstract»

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  • Numerical optimization of 3-D SAR distributions in cylindrical models for electromagnetic hyperthermia

    Page(s): 1246 - 1255
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    Numerically optimized specific absorption rate (SAR) distributions in a source-free three-dimensional multilayered concentric cylindrical (MCC) model are presented. The fields were expanded in the modes of the MCC. Cost functions which mathematically specify the relative weight assigned to differences between an SAR distribution and a desired SAR distribution were defined. The coefficients of the modes, which minimize the cost function, were obtained using gradient search optimization methods. The optimized SAR distributions shown were computed using three cost functions and two radial locations for the center of the region where the desired SAR is largest. A five-layered model, including the outer water layer for cooling and improved matching with the source, was used. The frequency was 70 MHz. The current and charge distributions computed on a perfectly conducting cylindrical surface just outside the model are given. The surface current and charge distributions depends strongly on the relative importance of the cost for acute heat and systemic heat. A technique is developed for generating a new set of basis functions for reducing the number of unknowns to be optimized. View full abstract»

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  • Quantitative shape descriptors of left ventricular cine-CT images

    Page(s): 1256 - 1261
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    In order to assess regional diastolic function of the left ventricle (LV), LV rapid-acquisition computed tomographic (cine-CT) images were used to build finite element models. To quantitatively evaluate the accuracy of the geometric reconstruction technique used in building these models, a new measure of shape similarity is introduced. The results obtained from the new measure were compared and contrasted to the results obtained from traditional shape similarity measures. All of these measures were used to compare the endocardial and epicardial LV contours obtained from video images of the same hearts. The results show that the imaging procedure accurately reproduces shape, and further suggest that the descriptor shows the sensitivity and resolution required to distinguish between images separated by as little as 3 mm. View full abstract»

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  • Deconvolution of tracer and dilution data using the Wiener filter

    Page(s): 1262 - 1266
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    The application of the Wiener filter to the deconvolution of tracer-type signals, i.e., any smooth concentration signals of biological origin, was investigated. This led to a more fundamental investigation of the Wiener filter itself, because tracer-type signals are invariably well described by parametric curves consisting of polynomials or sums of exponential functions. It is shown that better results are achieved with the Wiener filter if the model of the signal is not particularly accurate, whereas with a very accurate model it is better to deconvolve the model itself. The point at which the two deconvolution approaches perform comparably occurs when the error in the model is of a similar magnitude to the noise. View full abstract»

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  • Numerical implementation of sealed-end boundary conditions in cable theory

    Page(s): 1266 - 1271
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    The cable theory used for modeling voltage distributions in spatially extended neurons or other excitable cells, such as cells found in cardiac tissue, is reviewed. The theory is based on the observation that the intracellular electrical potential varies much more along a long nerve fiber than between points inside the fiber in a plane perpendicular to the fiber axis. This facilitates the mathematical analysis, since the spatial dimension of the differential equations for the intracellular voltage is reduced from three to one. It is shown that a frequently used numerical implementation of von Neumann boundary conditions (zero inflowing current) in cable theory is incorrect. Correct implementations are given, and it is shown that they yield results in good agreement with known analytical solutions. View full abstract»

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  • A bivariate version of Andrews plots

    Page(s): 1271 - 1274
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    A bivariate version of Andrews plots for naturally paired multivariate date is introduced. The bivariate Andrews plots are space curves, and are particularly effective for revealing patterns and clusters when depicted dynamically. Projections of the bivariate Andrews plots recover the familiar univariate Andrews plots. As an example, a series of experiments conducted to characterize the neurologic and morphologic consequences of acute cerebral artery occlusion in an animal (baboon) model and to evaluate the ability of antithrombotic therapy to reverse cerebral ischemia following acute thrombotic stroke is described. Bivariate Andrews plots of the paired latencies and amplitudes were drawn. It is shown that the dynamic display of the space curves provides an immediate means of visualizing similarities and differences, without invoking formal statistical tests. 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