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Showing papers in "IEEE Transactions on Biomedical Engineering in 1987"


Journal ArticleDOI
TL;DR: An improved electrical impedance tomographic reconstruction algorithm is presented that is generally guaranteed to converge and provides significantly better reconstructions than any of the other methods.
Abstract: An improved electrical impedance tomographic reconstruction algorithm is presented that is generally guaranteed to converge. The algorithm is attractive for several reasons. A modified Newton?Raphson method varies a finite-element model of resistivities to fit a set of voltage measurements in a least-squared sense. Two procedures for calculating the Jacobian matrix are derived. One is standard, while the other is based on the compensation theorem. This second procedure is more efficient for computations, and just as accurate as the standard one. The inherent ill-conditioning in the approximate Hessian matrix of the linearized system is eliminated using the Marquardt method. Results from two-dimensional computer simulations are compared to four other reconstruction algorithms, which are based on methods proposed by other authors. The modified Newton?Raphson method provided significantly better reconstructions than any of the other methods. The algorithms compared are the perturbation, equipotential, iterative-equipotential, and the double-constraint methods. The modified Newton?Raphson method was found to be sensitive to measurement error, but future work in designing electrode-probing configurations is expected to reduce this sensitivity.

608 citations


Journal ArticleDOI
TL;DR: A new technique for blood velocity imaging based on tracking the motion of the speckle pattern produced by blood, which unlike Doppler velocity determinations, these are angle independent.
Abstract: We present a new technique for blood velocity imaging based on tracking the motion of the speckle pattern produced by blood. Unlike Doppler velocity determinations, these are angle independent. Initial in vivo experiments yield promising results.

434 citations


Journal ArticleDOI
TL;DR: Scalp current density (SCD) makes possible the identification of scalp sources and sinks of current and its peaks and troughs are sharper than those of the scalp potential (SP).
Abstract: Scalp current density (SCD) makes possible the identification of scalp sources and sinks of current. SCD is reference independent and its peaks and troughs are sharper than those of the scalp potential (SP). SCD, by comparison to SP, reflects mainly the activity of cortical generators. SCD mapping appears to be a valuable tool to spatially split smeared SP distribution due to simultaneously active generators. The SCD map may be computed from any sufficiently smooth mathematical SP map. An evaluation of the error of SCD estimation is given for a surface spline method of interpolation of SP. An example of the simultaneous use of SP and SCD in the analysis of somatosensory evoked data is given.

423 citations


Journal ArticleDOI
TL;DR: It is numerically found that cavities in the skull disturb the inverse solution especially when the dipole is oriented toward the cavities, which does not change the significance of the results obtained by the present method.
Abstract: A method of localizing an electrical dipole in the brain from the scalp potential distribution has been developed with the aid of the boundary element method, in which a real geometry of the head is exactly taken into account and homogeneous electrical conductivity is assumed. Accuracy of the method was evaluated through animal experiments with a cat in which a current dipole was artificially generated in the brain. Deviation of the estimated dipole location from the true one was not random, but rather systematic (probably due to in-homogeneous conductivity distribution). It is numerically found that cavities in the skull disturb the inverse solution especially when the dipole is oriented toward the cavities. In vivo tests of the method were also done for primary somatosensory evoked potentials as a response to median nerve stimulation of a cat and myoclonic EEG. Although the homogeneous approximation was made, it does not change the significance of the results obtained by the present method.

323 citations


Journal ArticleDOI
TL;DR: Through the use of semicustom integrated circuit technology, an implantable muscle stimulator has been developed that is small, lightweight, has low power consumption, and is intended for permanent usage.
Abstract: Through the use of semicustom integrated circuit technology, an implantable muscle stimulator has been developed. The unit is small, lightweight, has low power consumption, and is intended for permanent usage. The stimulator circuitry is externally controlled and powered by a single encoded radio frequency carrier. Up to eight independently controlled stimulus output channels are provided, with output channel selection, stimulus pulse width, and stimulus pulse frequency under external control. A constant current biphasic stimulus pulse is used, in which the stimulus current amplitude can be preset by a single resistor value. The stimulator circuitry has been implemented in thick film hybrid form, and has undergone laboratory evaluation for 48 months.

284 citations


Journal ArticleDOI
TL;DR: A detailed theoretical analysis of misalignment effects in RF coil systems, including lateral and angular misalignments, is presented.
Abstract: Radio-frequency (RF) coils are used extensively in the design of implantable devices for transdermal power and data transmission. The practical issues of coil misalignments and configurations have not been investigated, and this paper presents a detailed theoretical analysis of misalignment effects in RF coil systems, including lateral and angular misalignments. Formulas are derived for the mutual inductance and, whenever possible, simplified upper bounds and lower bounds of the coupling coefficient are provided. A design procedure is established to maximize coil coupling for a given configuration, and a companion paper [1] discusses a circuit design technique to reduce the effects of misalignment on transmission efficiency.

263 citations


Journal ArticleDOI
TL;DR: A new method of desensitizing the gain of an inductive link to the mutual coupling of its inductors when the coupling varies due to geometrical misalignments is described.
Abstract: This paper describes a new method of desensitizing the gain of an inductive link to the mutual coupling of its inductors. When the coupling varies due to geometrical misalignments [1] this design method guarantees good efficiency and a large bandwidth. The mathematics for four link combinations are presented, and examples of the link efficiency and bandwidth for one of the combinations are shown and discussed.

235 citations


Journal ArticleDOI
TL;DR: The theory and experimental feasibility of measuring Doppler spectra in transverse geometries is presently investigated, finding that the probing of flows transverse to the axis of finite diameter beams, particularly focused beams, is feasible.
Abstract: It is an accepted fact that transverse Doppler effects of the first order in v/c are nonexistent for all physical wave phenomena, including acoustics, i.e., the Doppler effect is zero for radiation normal to the direction of motion. However, this statement assumes that the incident field is a plane wave, which is not true in general for finite aperture sources. Consequently, the probing of flows transverse to the axis of finite diameter beams, particularly focused beams, is feasible. This geometry will be advantageous in many applications where the classical orientation of the sound beam, oblique to the flow, is not possible. With this motivation in mind, the theory and experimental feasibility of measuring Doppler spectra in transverse geometries is presently investigated.

191 citations


Journal ArticleDOI
TL;DR: The results obtained demonstrate that the FDTD method is capable of calculating internal SAR distribution with acceptable accuracy and is evaluated by comparing its results to analytic solutions in two and three dimensions.
Abstract: Although there are acceptable methods for calculating whole body electromagnetic absorption, no completely acceptable method for calculating the local specific absorption rate (SAR) at points within the body has been developed. Frequency domain methods, such as the method of moments (MoM) have achieved some success; however, MoM requires computer storage on the order of (3N) 2 and computation time on the order of (3N) 3 where N is the number of cells. The finite-difference time-domain (FDTD) method has been employed extensively in calculating the scattering of metallic objects, and recently is seeing some use in calculating the interaction of EM fields with complex, lossy dielectric bodies. Since the FDTD method has storage and time requirements proportional to N, it presents an attractive alternative to calculating SAR distribution in large bodies. This paper describes the FDTD method and evaluates it by comparing its results to analytic solutions in two and three dimensions. The utility of the FDTD method is demonstrated by a 3D scan of the human torso. The results obtained demonstrate that the FDTD method is capable of calculating internal SAR distribution with acceptable accuracy. With the availability of supercomputers, such as the CRAY II, the calculation of SAR distribution in a man model of 50 000 cells (1.27 cm per cell) appears to be feasible.

183 citations


Journal ArticleDOI
TL;DR: The generalized CPG model is shown to be versatile enough that it can also generate various n-legged gaits and spinal undulatory motions, as in the swimming motions of a fish.
Abstract: A set of van der Pol oscillators is arranged in a network in which each oscillator is coupled to each other oscillator. Through the selection of coupling coefficients, the network is made to appear as a ring and as a chain of coupled oscillators. Each oscillator is provided with amplitude, frequency, and offset parameters which have analytically indeterminable effects on the output waves. These systems are simulated on the digital computer in order to study the amplitude, frequency, offset, and phase relationships of the waves versus parameter changes. Based on the simulations, systems of coupled oscillators are configured so that they exhibit stable patterns of signals which can be used to model the central pattern generator (CPG) of living organisms. Using a simple biped as an example locomotory system, the CPG model generates control signals for simulated walking and jumping maneuvers. It is shown that with parameter adjustments, as guided by the simulations, the model can be made to generate kinematic trajectories which closely resemble those for the human walking gait. Further-more, minor tuning of these parameters along with some algebraic sign changes of coupling coefficients can effect a transition in the trajectories to those of a two-legged hopping gait. The generalized CPG model is shown to be versatile enough that it can also generate various n-legged gaits and spinal undulatory motions, as in the swimming motions of a fish.

180 citations


Journal ArticleDOI
TL;DR: This paper presents and tests a computer method to quantify the motion of the heart from digitized image sequences that computes on every point of an image the two-dimensional velocity vector which characterizes its motion from this image to the next.
Abstract: In two-dimensional echocardiography the study of the motion of the heart, especially of the left ventricle, is of central interest Although the clinician can see this motion on real-time two-dimensional echocardiograms, its quantification can still be greatly improved This paper presents and tests a computer method to quantify the motion of the heart from digitized image sequences This method computes on every point of an image the two-dimensional velocity vector which characterizes its motion from this image to the next This approach has the following advantages: 1) border recognition algorithms are no longer needed, 2) motion is not restricted to its radial component, and 3) motion information is available on every point of the image

Journal ArticleDOI
TL;DR: The major conclusion of this work is that the inversion problem is severely ill-posed and the choice of model and estimation algorithm are crucial in obtaining reasonable solutions.
Abstract: In this paper, we discuss several aspects of a potential new medical imaging modality for producing a quantitative three-dimensional map of neuron current densities associated with brain function. The neuromagnetic image is produced by reconstructing a current dipole field from external magnetic field measurements made with an array of superconducting quantum interference device (SQUID) detectors. This field is produced by numerical inversion of the Biot-Savart equation. The purpose of the work is to investigate fundamental limits on the feasibility of the proposed system under ideal conditions. The following problems are addressed: 1) What are the factors limiting resolution of the system? 2) What is a suitable model for neural activity in the brain? 3) What classes of algorithms are suitable for estimating the model parameters? The major conclusion of this work is that the inversion problem is severely ill-posed and the choice of model and estimation algorithm are crucial in obtaining reasonable solutions. A class of solutions, termed minimum dipole, is proposed as a means of obtaining more acceptable results.

Journal ArticleDOI
TL;DR: Even in high levels of muscle contraction, single motor unit impulses that are suitably shaped by filtering can be repeatedly recognized in the surface EMG signal.
Abstract: Complementary to its conventional applications, surface EMG is also suited to gain more detailed information on the functional state of a muscle, when measurement configurations with smaller pickup areas are used. A new category of suitable measurement configurations is obtained by application of the spatial filtering principle to electromyography. In a spatial filter unit, the signals of several recording electrodes are combined to form one output signal channel. The filter characteristic is determined by the weighting factors used and by the geometrical arrangement of the electrodes. Extended multielectrode arrays and multichannel recording make possible the detection of correlated excitations at different sites of the muscle. Even in high levels of muscle contraction, single motor unit impulses that are suitably shaped by filtering can be repeatedly recognized in the surface EMG signal. In clinical studies, pathologically shaped impulses have been identified indicating multiple innervation zones. The initiation and the propagation of excitation within single motor units can be detected with improved accuracy even from very small muscles.

Journal ArticleDOI
Cees J. Stok1
TL;DR: It is found that sphere radii and conductivities influence especially the strength of the EEG equivalent dipole and not its location or direction, and the MEG produces better location estimates than the EEG whereas the reverse is found for the component estimates.
Abstract: This paper deals with source localization and strength estimation based on EEG and MEG data. It describes an estimation method (inverse procedure) which uses a four-spheres model of the head and a single current dipole. The dependency of the inverse solution on model parameters is investigated. It is found that sphere radii and conductivities influence especially the strength of the EEG equivalent dipole and not its location or direction. The influence on the equivalent dipole of the gradiometer is investigated. In general the MEG produces better location estimates than the EEG whereas the reverse is found for the component estimates. An inverse solution simultaneously based on EEG and MEG data appears slightly better than the average of separate EEG and MEG solutions. Variances of parameter estimators which can be calculated on the basis of a linear approximation of the model, were tested by Monte Carlo simulations.

Journal ArticleDOI
TL;DR: The AF technique shows promise for requiring fewer ensembles than averaging to attain adequate signal quality, and theoretically that the filter output converges to the least square estimate of the underlying signal.
Abstract: We present an adaptive filtering (AF) technique for rapid processing of evoked potentials (EP). The AF algorithm minimizes the mean-square error (MSE) between successive ensembles. We demonstrate theoretically that the filter output converges to the least square estimate of the underlying signal. Computer simulations with known signal and added noise show that AF produces lower MSE than ensemble averaging. We also compare results of AF to those obtained by ensemble averaging for some EP recorded from animals and humans. For very noisy EP recordings, we propose techniques that combine AF and ensemble averaging. The AF technique shows promise for requiring fewer ensembles than averaging to attain adequate signal quality.

Journal ArticleDOI
TL;DR: This technique offers a new flexibility in the design of selective EMG measurement configurations by means of a given simple model of an excited motor unit and results compare well to the previously described experimental signals.
Abstract: Spatial filtering, particularly common in the field of engineering, is adapted in theory and practice to the filtering of propagating spatial EMG signals. This technique offers a new flexibility in the design of selective EMG measurement configurations. Longitudinal as well as two-dimensional spatial filters can be used. The conditions for the design of suitable spatial filters are deduced by signal theory. The performances of different selected configurations are compared by means of a given simple model of an excited motor unit. The modeling results compare well to the previously described experimental signals.

Journal ArticleDOI
TL;DR: An electrooptical laser Doppler system and technique of data analysis that provides absolute measurements of the speed of red blood cells flowing at discrete, selectable sites in the retinal vasculature concludes that measurements on retinal arteries are less susceptible to experimental artifacts and provide more information than do measurements onretinal veins.
Abstract: We describe an electrooptical laser Doppler system and technique of data analysis that provides absolute measurements of the speed of red blood cells flowing at discrete, selectable sites in the retinal vasculature. We present in vitro test measurements of the instrumentation as well as an example of an in vivo measurement from a patient with retinal vascular disease. We also present experimental data leading to the derivation of the relationship between the blood speeds measured in retinal arteries during the minimum diastolic and maximum systolic phases of the cardiac cycle and the time-averaged blood speed. Mean blood flow rate is calculated using the time-averaged speed and the cross-sectional area of the vessel at the measurement site. We discuss the criteria for selection of the measurement sites and assess the reproducibility of the measurements. We conclude that measurements on retinal arteries are less susceptible to experimental artifacts and provide more information than do measurements on retinal veins. The system is currently being used clinically in studies of retinal circulatory alterations in patients with diabetic retinopathy, arterial occlusive disease, retinal detachment, and carotid artery disease.

Journal ArticleDOI
TL;DR: A Green's function approach has been used to solve Lapalce's equation for the quasi-static fields of a recessed, disk electrode and it is indicated that a recession has a more uniform current density profile than a surface mounted electrode.
Abstract: A Green's function approach has been used to solve Lapalce's equation for the quasi-static fields of a recessed, disk electrode. The resulting integral equation was solved numerically using the moment method. An analysis of the error in the approximate solution shows that it must be less than 7 percent for the cases studied. The calculations indicate that a recessed electrode has a more uniform current density profile than a surface mounted electrode. This is true both at the electrode surface, and at the electrode carrier?tissue junction. The significance of this finding is discussed as is its application to electrochemical, histopathological, and physiological studies of neural prostheses. The clinical use of recessed electrodes in cochlear implants is recommended.

Journal ArticleDOI
TL;DR: This study examines the distribution of the transmembrane potential in the periodic strand of cardiac muscle established by configurations of sources similar to those arising during extracellular stimulation and defibrillation, during intracellular stimulation, and during propagation of action potential to suggest the mechanism of propagation in discrete structures may be similar to that of the continuous fiber.
Abstract: This study examines the distribution of the transmembrane potential in the periodic strand of cardiac muscle established by configurations of sources similar to those arising during extracellular stimulation and defibrillation, during intracellular stimulation, and during propagation of action potential. The closed-form solution indicates that during extracellular stimulation with large current and during defibrillation, the periodic component of the transmembrane potential is very important. We postulate that this periodic component causes the depolarization or defibrillation in cardiac muscle, which is different from the depolarization mechanism for a continuous fiber. On the other hand, during propagation and intracellular stimulation, the periodic component only slightly modifies the monotonic decrease of the transmembrane potential, which suggests that the mechanism of propagation in discrete structures may be similar to that of the continuous fiber.

Journal ArticleDOI
TL;DR: The balance test was able to identify up to three of five vestibular patients and five of five elderly fallers, at a false positive rate of 25 percent in the normal subjects, but no differences between males and females.
Abstract: A balance testing methodology has been developed based on a posture control model which defines relative stability by the degree to which a transient postural perturbation causes the center-of-pressure on the feet to approach the limits of the base-of-support. To minimize anticipatory adaptations and to ensure subject safety, the balance test uses a small-amplitude continuous random or pseudo-random perturbation. The data are used to identify an input-output model, which is then used to predict large-amplitude transient response. Sixtyfour normal subjects were tested, as well as five patients with vestibular lesions and five elderly subjects with a history of falling. Tests were performed with eyes open (EO) and blindfolded (BF), and the EO/BF ratio was calculated. The results showed highly significant differences between young (20-40) and elderly (61-79) normals, but no differences between males and females. In using the balance test to identify the balance-impaired individuals, the BF and EO/BF data provided higher success rates than the EO data. Depending on the modeling method used, the balance test was able to identify up to three of five vestibular patients and five of five elderly fallers, at a false positive rate of 25 percent in the normal subjects.

Journal ArticleDOI
TL;DR: A method is presented here to reproducibly quantify this collagen arrangement, which should be useful in studies on ligament healing and growth.
Abstract: Collagen fibers and their component fibrils make up the protenaceous " backbone" of most tissues and provide the majority of their resistance to tensile loading. Spatial orientation of collagen fibrils is an important factor in determining tissue properties. This is particularly true in ligament tissue, since ligaments must be loose enough to allow joints to move but tight enough to prevent joint surfaces from separating. A method is presented here to reproducibly quantify this collagen arrangement, which should be useful in studies on ligament healing and growth.

Journal ArticleDOI
TL;DR: A multiple-model adaptive control procedure for sodium nitroprusside regulation of arterial pressure with Pole-placement, via state-variable feedback, included in the controller to achieve desired performance characteristics.
Abstract: This paper presents a multiple-model adaptive control procedure for sodium nitroprusside regulation of arterial pressure. Pole-placement, via state-variable feedback, is included in the controller to achieve desired performance characteristics. A Smith predictor in the controller effectively removes the infusion delay time, thus simplifying the control analysis and design. Proportional-plus-integral control is used to achieve zero steady-state error. Computer simulations on linear transfer function models with varying gains, time constants, and infusion delays demonstrate the robustness of this multiple-model controller. Additional simulations on nonlinear, pulsatile-flow cardiovascular models lend further support to the ultimate use of this controller for blood-pressure regulation.

Journal ArticleDOI
TL;DR: An investigation of the ability of the autoregressive (AR) model to describe the spectrum of the processes underlying the recorded surface EMG, carrying out SEMG measurements on the biceps brachii muscle with fixed surface electrodes arrangement and isotonic conditions.
Abstract: The following is an investigation of the ability of the autoregressive (AR) model to describe the spectrum of the processes underlying the recorded surface EMG. Surface EMG (SEMG) spectrum is influenced by two major factors; one attributed to the motor units (MU) firing rate and the second, the higher frequency one, to the morphology of the action potentials (AP) traveling along the muscle fiber. In the present paper, SEMG measurements were carried out on the biceps brachii muscle with fixed surface electrodes arrangement and isotonic conditions. Sufficient averaging of 0.5 s segments enabled the identification of the low-frequency peak related to the firing rates of the MU's.

Journal ArticleDOI
TL;DR: Details of a microcomputer system developed to segment the phonocardiogram signal (PCG) and characterize murmurs are presented and the use of these parameters for the detection and classification of murmurs is discussed.
Abstract: We present here details of a microcomputer system developed to segment the phonocardiogram signal (PCG) and characterize murmurs. Using the ECG and carotid pulse as references, the PCG is segmented into systolic and diastolic parts. Four parameters representing the time and frequency domain characteristics of the signal segments are then computed. Results of application of the methods to 47 phonocardiogram signals are presented. The use of these parameters for the detection and classification of murmurs is discussed.

Journal ArticleDOI
TL;DR: A three-dimensional computer model has been constructed to simulate the ventricular depolarization and repolarization processes in a human heart, and the resulting ECG, VCG, and BSPM's are within the expected range of clinical observations.
Abstract: A three-dimensional computer model has been constructed to simulate the ventricular depolarization and repolarization processes in a human heart. The electrocardiogram (ECG), the vectorcardiogram(VCG), and the body surface potential map (BSPM) during the QRS-T period are obtained automatically under certain heart conditions such as bundle branch block and myocardial infarctions. The ventricles, together with bundle branches and the Purkinje fibers, are composed of approximately 50 000 cell units which are arranged in a cubic close-packed structure. A different action potential waveform was assigned to each unit. The heart model is mounted in a homogeneous human torso model. Electric dipoles, which are proportional to the spatial gradient of the action potential, are generated in all the cell units. These dipoles give rise to a potential distribution on the torso surface, which is calculated by means of the boundary element method. The resulting ECG's, VCG's, and BSPM's are within the expected range of clinical observations.

Journal ArticleDOI
TL;DR: Reduction of the maximal firing rate from 55 to 40 pps showed that although minimization of fatigue at a cost of 10 percent reduction in the maximal force is possible, the correlation of the force response to the input signal remains high and linear.
Abstract: A computer-controlled, dual-channel neuromuscular stimulation system capable of manipulating skeletal muscle force with a wide range of action potential firing rates and motor-unit recruitment control strategies was designed and evaluated on the m. gastrocnemius muscle of the cat. The muscle force could be controlled with control strategies in which motor unit recruitment accounted for from 50 percent and up to 100 percent of the initial muscle force while firing rate induced the remaining force segment. The force response to linearly increasing recruitment was linear, whereas a saturation nonlinearity was evident in response to the firing rate input. Initial and terminal nonlinear force segments during 100 percent recruitment range were shown to be due to the viscoelastic components of the muscle fibers and their tendons. Recruitment of the muscle's motor units at rates that generated from 36 percent/s and up to 360 percent/s of the maximal force range was shown to correlate linearly to the input stimulus (R 0.9889). Reduction of the maximal firing rate from 55 to 40 pps showed that although minimization of fatigue at a cost of 10 percent reduction in the maximal force is possible, the correlation of the force response to the input signal remains high (R 0.9929) and linear. Some preliminary conclusions about rehabilitative applications were drawn based on the data presented in conjunction with previous studies.

Journal ArticleDOI
TL;DR: A discrete time adaptive control system for electrically stimulated muscle has been designed and evaluated experimentally and performance was evaluated on the basis of stability and responses to step, ramp, and sinusoidal inputs.
Abstract: A discrete time adaptive control system for electrically stimulated muscle has been designed and evaluated experimentally. The control system is based on a previously developed discrete time model of electrically stimulated muscle. Performance was evaluated on the basis of stability and responses to step, ramp, and sinusoidal inputs. Cat tibialis anterior muscles that had been previously electrically exercised were activated to control ankle joint torque via chronically implanted epimysial electrodes.

Journal ArticleDOI
TL;DR: The results demonstrate the feasibility of using CAMAC for multivariable drug delivery, but they indicate the need for further work before clinical applications are attempted.
Abstract: An adaptive algorithm (CAMAC, control advance moving average controller) to control multiinput/multioutput physiological systems has been implemented and tested. The algorithm is a self-tuning controller that determines the input on the basis of the expected difference between the output and desired output at a time interval equal to or greater than the system dead time. The algorithm was used to simultaneously control mean arterial pressure and cardiac output in anesthetized dogs by the simultaneous computer-controlled infusion of sodium nitroprusside and dobutamine. The results demonstrate the feasibility of using CAMAC for multivariable drug delivery, but they indicate the need for further work before clinical applications are attempted.

Journal ArticleDOI
TL;DR: The design and prototype model of a nonvibrating fingertip search display device that translates a visual image into a contour map of raised pins similar to transitory braille, designed for use in experiments to determine the importance of fingertip exploration in tactile vision substitution.
Abstract: This paper describes the design and prototype model of a nonvibrating fingertip search display device. It was designed for use in experiments to determine the importance of fingertip exploration in tactile vision substitution. An 8 ×8 array of miniature dc solenoids mounted on 5 mm centers forms a raised two-dimensional display. With the aid of an IBM PC, it translates a visual image into a contour map of raised pins similar to transitory braille. The four possible pin heights of 0, 0.33, 0.67, and 1 mm represent discrete levels of image intensity. The user controls the location and resolution of the image sent from the IBM PC to the display by moving a mouse.

Journal ArticleDOI
TL;DR: It is concluded that the restoration of physiological blood glucose control in insulin-dependent diabetes requires dosage parameters which are either continually adapted to the actual situation (adaptive control) or are optimized to meet the individual's needs.
Abstract: To test the hypothesis that only an adaptive algorithm would guarantee optimal feedback control of glycemia in insulin-dependent diabetes, fasting chronically diabetic dogs at rest were subjected to short-term artificial beta cell treatment. Insulin was applied intravenously and an oral glucose load was given during the experiment. Employing the same dosing algorithm, three different control strategies were employed in a random order on different days: adaptive control (minimum variance controller, Test A), fixed command control using on-line parameter estimates (Test B), and fixed command control using off-line individually optimized dosage constants (Test C). Comparison was made to nondiabetic control animals. The glycemic profiles were entirely normal in Test A and C, but were distinctly elevated in Test B. The peripheral hyperinsulinaemia could, however, not be avoided by adaptive control. It is concluded that the restoration of physiological blood glucose control in insulin-dependent diabetes requires dosage parameters which are either continually adapted to the actual situation (adaptive control) or are optimized to meet the individual's needs. In the latter case, fixed command control may be employed. Peripheral hyperinsulinaemia cannot be avoided as long as insulin is administered by a posthepatic route.