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Biomedical Engineering, IEEE Transactions on

Issue 1 • Date Jan. 1991

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Displaying Results 1 - 14 of 14
  • Electrotactile and vibrotactile displays for sensory substitution systems

    Publication Year: 1991 , Page(s): 1 - 16
    Cited by:  Papers (148)  |  Patents (38)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1683 KB)  

    Sensory substitution systems provide their users with environmental information through a human sensory channel (eye, ear, or skin) different from that normally used or with the information processed in some useful way. The authors review the methods used to present visual, auditory, and modified tactile information to the skin and discuss present and potential future applications of sensory substitution, including tactile vision substitution (TVS), tactile auditory substitution, and remote tactile sensing or feedback (teletouch). The relevant sensory physiology of the skin, including the mechanisms of normal touch and the mechanisms and sensations associated with electrical stimulation of the skin using surface electrodes (electrotactile, or electrocutaneous, stimulation), is reviewed. The information-processing ability of the tactile sense and its relevance to sensory substitution is briefly summarized. The limitations of current tactile display technologies are discussed, and areas requiring further research for sensory substitution systems to become more practical are suggested. View full abstract»

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  • Feedback regulation of hand grasp opening and contact force during stimulation of paralyzed muscle

    Publication Year: 1991 , Page(s): 17 - 28
    Cited by:  Papers (43)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1126 KB)  

    A fixed-parameter, discrete-time, first-order, feedback control system is described for regulating grasp during electrical stimulation of paralyzed muscles of the hand. The stiffness of the grasp (the relationship between grasp force and grasp opening) is kept constant by linearly combining force and position feedback signals. Thus, a single continuous command signal can control the size of the grasp opening prior to object acquisition and both grasp and opening after contact. The controller achieves this change in controlled variables by scaling and summing the force and position feedback signals, rather than by a discrete switch in control strategy. Experimental tests of the control system in quadriplegic subjects show that control can be obtained over conditions ranging from unloaded position regulation is isometric force regulation as well as in the transition between these conditions. The robustness of the control system was evaluated during force regulation with isometric loads. Step response rise time and overshoot were much more dependent on system gain than on the location of the controller zero. Responses with a rise time of less than and 2 s an overshoot of less than 30% were obtained over a gain range up to 10, indicating good robustness to muscle gain reductions such as might be caused by fatigue. View full abstract»

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  • Cognitive feedback for use with FES upper extremity neuroprostheses

    Publication Year: 1991 , Page(s): 29 - 38
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1070 KB)  

    The development of two sensory substitutions systems that provide cognitive feedback for FES (functional electrical stimulation) hand-grasp-restoration neuroprostheses is described. One system uses an array of five electrodes to provide machine status information and a spatially encoded representation of the command signal that a quadriplegic individual generates to achieve proportional grasp control. Only one electrode site is active at any given instant, and a second informational channel is superimposed on the spatial position channel by modulating the frequency of the stimulus pulses. The frequency-modulated feedback channel signals six levels of force developed at the finger tips during prehension activities. The second sensory system is an integral part of an implanted FES system and utilizes a single subdermally placed electrode to display machine status information and a five-level frequency code for feedback of the user-generated grasp control signal. The multielectrode feedback system was implemented for laboratory studies using surface-mounted electrodes, although its design will ultimately incorporate subdermal electrodes to provide a highly cosmetic and unencumbering system. View full abstract»

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  • Adaptive control of closed-circuit anesthesia

    Publication Year: 1991 , Page(s): 39 - 47
    Cited by:  Papers (24)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (755 KB)  

    An explicit adaptive controller for the control of closed-circuit anesthesia (CCA) has been developed. This system controls the end-tidal oxygen and anesthetic gas concentrations as well as the circuit volume. The CCA process was modeled by writing mass balance equations. Simplifying assumptions yielded a bilinear single-input-single-output model for the anesthetic gas concentration and a bilinear multiple-input-multiple-output model for the circuit volume and oxygen concentration. One-step-ahead controllers were used to control these two subsystems. Simulations showed that the control performance was most sensitive to the gas uptakes. Three independent, least-mean-squares estimation schemes were implemented to estimate the uptakes of oxygen, nitrous oxide, and anesthetic gas. These estimates were used in the control law and resulted in explicit adaptive control. The performance of the adaptive controller was compared to that of a fixed controller (with precalculated gas uptakes) in five animal experiments. The adaptive controller performed better than the fixed controller in all cases. View full abstract»

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  • Systematic autoregulation counteracts the carotid baroreflex

    Publication Year: 1991 , Page(s): 48 - 56
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (894 KB)  

    The interaction between autoregulation and baroregulation and its effect on the gains of the short-term pressure regulatory system were studied by performing open- and closed-loop experiments in the same five anesthetized, vagotomized dogs and by analyzing the data using a novel model. With carotid pressure constant (no baroregulation), the pressure-flow data were convex to the flow axis, indicating the presence of autoregulation. When baroregulation was present, the data were convex to the pressure axis. The proposed model was able to fit the data as measured in both cases. From the fitting procedure, the zero-flow pressure intercept, the autoregulation resistance gain, and the baroregulation resistance gain were estimated. It is concluded that if autoregulation is present it affects the values of baroreflex gains estimated from both closed- and open-loop experiments. The autoregulation gain can be estimated from steady-state systemic pressure-flow data measured after vagotomy and with the carotid pressure constant. Then, from measurements of systemic pressure-flow data performed after restoring the hydraulic connection between carotid and aortic areas, the gains of the carotid baroreflex can be estimated with the aid of the proposed model. View full abstract»

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  • A semiclosed-loop algorithm for the control of blood glucose levels in diabetics

    Publication Year: 1991 , Page(s): 57 - 61
    Cited by:  Papers (48)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (467 KB)  

    A theoretical analysis of the control of plasma glucose levels in diabetic individuals is undertaken using a simple mathematical model of the dynamics of glucose and insulin interaction in the blood system. Mathematical optimization techniques are applied to the mathematical model to derive insulin infusion programs for the control of blood levels in diabetic individuals. Based on the results of the mathematical optimization, a semiclosed-loop algorithm is proposed for continuous insulin delivery to diabetic patients. The algorithm is based on three hourly plasma glucose samples. A theoretical evaluation of the effectiveness of this algorithm shows that it is superior to two existing algorithms in controlling hyperglycemia. A glucose infusion term representing the effect of glucose intake resulting from a meal is introduced into the model equations. Various insulin programs for the control of plasma glucose levels following a meal are then assessed. The theoretical results suggest that the most effective short-term control is achieved by an insulin infusion program which incorporates an injection to coincide with the meal. View full abstract»

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  • Noninvasive measurement of compliance of human leg arteries

    Publication Year: 1991 , Page(s): 62 - 67
    Cited by:  Papers (3)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    Electrical impedance plethysmography has been evaluated for early detection of peripheral atherosclerosis. A pressure cuff was wrapped around the lower leg and the cuff pressure increased. Two circumferential electrodes glued in the middle of the cuff recorded with impedance pulse, from which the arterial pulse volume was calculated. The ratio of maximal arterial volume change to the pulse pressure was determined as a measure of maximal compliance C p. Based on the data from 118 human subjects, C p was found to correlate well with known cardiovascular risk factors. For example, C p decreased on the average from 3.08 to 1.92 mu L/mmHg/cm in groups of subjects of increasing age from 22 to 70 yr. Subjects on a regular exercise program had an average value of 3.86, while those with proven peripheral vascular disease had a value of 0.70. In a related pathologic validation study on 15 monkeys fed a cholesterol-control diet, a good correlation was found between the limb peak compliance and morphometric data obtained from iliac and carotid arteries. View full abstract»

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  • Multisite microprobes for neural recordings

    Publication Year: 1991 , Page(s): 68 - 74
    Cited by:  Papers (19)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (882 KB)  

    Multisite, passive microprobes have been developed to allow simultaneous recording of action potential activity from multiple neurons at different locations in the brain. The microprobes were fabricated using standard integrated-circuit techniques. The probe is a planar structure that consists of gold electrodes sandwiched between two polyimide dielectric layers and bonded to a molybdenum structural support. Windows in the top dielectric layer expose the electrode sites and bonding pads. In two distinct versions of the probe, four or six recording sites of approximately 25 mu m 2 are arranged on a dagger-shaped structure which can penetrate the pia. The bonding pads and interconnect wires at the probe head are entirely encapsulated in a tubular fixture that is packed with silicone RTV and sealed with epoxy to protect the interconnections from contact with body fluids. The site impedances at 1 kHz are typically between 2 and 4 M Omega . Probe lifetimes for continuous immersion in physiological saline solution, as measured by impedance, have exceeded 750 h. The failure mechanism is believed to be due to moisture and ion absorption in the top dielectric layer. View full abstract»

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  • A low-noise demultiplexing system for active multichannel microelectrode arrays

    Publication Year: 1991 , Page(s): 75 - 81
    Cited by:  Papers (7)  |  Patents (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (753 KB)  

    The authors report a low-noise demultiplexing system capable of reconstructing multichannel single-unit neural signals derived from multiplexed microelectrode arrays. The overall multiplexing-demultiplexing system realizes ten channels, a per-channel gain of 68 dB, a bandwidth from 100 Hz to 6 kHz, and an equivalent noise level (referred to the probe input) of 13 mu V RMS. It provides for signaling over the power supply to allow the control of on-chip probe functions such as self-testing. The interchannel crosstalk is less than 3%, and switching noise is suppressed by blanking the transition intervals. The 200-kHz probe sample clock is tracked automatically over a range of 150 to 250 kHz. Neural signals as low as 20 mu V (typically 640 mu V at the demultiplexing system input) can be reconstructed. The overall system organization is compatible with the demultiplexing of as many as 40 time-multiplexed electrode channels from a single probe data line. View full abstract»

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  • Moving dipole inverse solutions using realistic torso models

    Publication Year: 1991 , Page(s): 82 - 84
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    A noniterative numerical solution for the potentials on the surfaces of a piecewise homogeneous volume conductor due to a current dipole is described. This forward solution has been used in electric and magnetic single moving dipole (SMD) inverse solutions that use a torso volume conductor model whose boundaries are specified numerically. Thus, the volume conductor model used by the inverse solutions need not be limited to simple geometric shapes; torso models of realistic shape can be used. View full abstract»

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  • Combined microwave heating and surface cooling of the cornea

    Publication Year: 1991 , Page(s): 85 - 91
    Cited by:  Papers (3)  |  Patents (36)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (743 KB)  

    The authors investigated a nonsurgical means of reshaping the cornea to correct hyperopia, keratoconus, or myopia. The object was to heat the central stroma of the cornea to the shrinkage temperature of collagen, 55-58 degrees C. The heating device was an open-ended, coaxial, near-field applicator driven at 2450 MHz; it incorporates cooling of the cornea surface by slow of saline. The system was investigated theoretically by computing the 2-D, axisymmetric temperature distribution with the finite-element method. The system was investigated experimentally by heating excised steer corneas. Histology showed that the system could shrink the stroma to a depth of 0.6 mm while sparing the epithelium in 75% of the cases; the diameter of shrinkage was 1.3 mm. Theory predicted a significantly deeper and narrower region of shrinkage than was observed. View full abstract»

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  • Heating patterns generated by phase modulation of a hexagonal array of interstitial antennas

    Publication Year: 1991 , Page(s): 92 - 97
    Cited by:  Papers (3)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (583 KB)  

    An array of six interstitial microwave antennas used for hyperthermia cancer treatment is investigated. The purpose is to generate both uniform and controlled nonuniform heating patterns in biological tissue by phase modulating the signals applied to each antenna. The array consists of six antennas positioned on the corners of a hexagon. The distance between two diagonal antennas is 4 cm. The distributions of absorbed power per unit mass within the array are computed and converted into temperature distributions through a thermal conduction simulation. The specific absorption rate and temperature patterns are presented in the lateral plane (perpendicular to the antennas) and the axial plane (parallel with the antennas). By proper phase modulation of microwave signals applied to each antenna, a uniform heating pattern can be produced within the entire array volume. A peripheral heating pattern can also be generated around the array by using the proper phase modulation. The modulation schemes for generating both types of heating patterns are discussed. View full abstract»

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  • Electromagnetic and thermal models of a water-cooled dipole radiating in a biological tissue

    Publication Year: 1991 , Page(s): 98 - 103
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (439 KB)  

    An insulated, water-cooled dipole, radiating in a biological tissue, is analyzed with a theoretical electromagnetic and thermal model. The SAR (specific absorption rate) and temperature distributions are calculated taking into account the effect of the water flowing inside the applicator. The steady-state temperatures in a dissipative medium, interacting with the dipole, are evaluated for several thicknesses of the external casing, water temperatures, and blood perfusions. A correct design of the external casing thickness and a proper choice of the temperature and flow velocity of water make it possible to control the wall temperature of the applicator within physiological limits. The influence of the blood perfusion on the temperature distribution is investigated. View full abstract»

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  • Epidural spinal cord stimulation: calculation of field potentials with special reference to dorsal column nerve fibers

    Publication Year: 1991 , Page(s): 104 - 110
    Cited by:  Papers (12)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (683 KB)  

    The effect of electrical stimulation with several electrode combinations on nerve fibers with different orientations in the spinal cord was investigated by computing the steady-state field potentials and activating functions. An infinite homogeneous model was used, and the spinal cord and its surrounding tissues where then modeled as an inhomogeneous anisotropic volume conductor. The effect of mediodorsal epidural stimulation was calculated. It was concluded that the cathodal stimulation, mediodorsally in the epidural space, longitudinal fibers are depolarized, but dorsoventral ones are hyperpolarized. With anodal stimulation the opposite will occur. It was found that parameters substantially affecting the potential distribution in the dorsal columns are the conductivity of the white matter and the width and the conductivity of the cerebrospinal fluid layer. 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