IEEE transactions on bio-medical engineering
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IEEE Trans Biomed Eng · Oct 1990
Charge density and charge per phase as cofactors in neural injury induced by electrical stimulation.
The possibility of neural injury during prolonged electrical stimulation of the brain imposes some constraints on the use of this technique for therapeutic and experimental applications. Stimulating electrodes of various sizes were used to investigate the interactions of two stimulus parameters, charge density and charge per phase, in determining the threshold of neural injury induced by electrical stimulation. Platinum electrodes ranging in size from 0.002 to 0.5 cm2 were implanted over the parietal cortex of adult cats. ⋯ The results show that charge density (as measured at the surface of the stimulating electrode), and charge per phase, interact in a synergistic manner to determine the threshold of stimulation-induced neural injury. This interaction occurs over a wide range of both parameters; for charge density from at least 10 to 800 microC/cm2 and, for charge per phase, from at least 0.05 to 5.0 microC per phase. The significance of these findings in elucidating the mechanisms underlying stimulation-induced injury is discussed.
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IEEE Trans Biomed Eng · Jul 1990
Point source nerve bundle stimulation: effects of fiber diameter and depth on simulated excitation.
Excitation response of different diameter myelinated nerve fibers situated at various depths within a cylindrical nerve bundle from the applied field of a point source electrode are analytically evaluated. For the potential field calculation, the fiber bundle is considered to be immersed in an infinite isotropic conductive medium and is idealized as an infinitely extending cylinder represented as an anisotropic bidomain (where electrical coupling from interstitial to intracellular space is included). ⋯ Stimulation level necessary for a nerve fiber to reach threshold is quantified in response to four descriptions of the volume conductor: the isotropic homogeneous case, the monodomain case, the bidomain case, and the "modified monodomain" case (where axial current is considered to flow through a parallel combination of longitudinal interstitial and intracellular resistive pathways, i.e., "complete" current redistribution). Model results indicate the importance of a bidomain representation of the nerve bundle, and provide insight into the relationship between the physical medium and the physiological properties of nerve fiber excitation.
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IEEE Trans Biomed Eng · Jul 1990
A nerve cuff technique for selective excitation of peripheral nerve trunk regions.
Numerical modeling and experimental testing of a nerve cuff technique for selective stimulation of superficial peripheral nerve trunk regions is presented. Two basic electrode configurations ("snug" cuff monopolar and tripolar longitudinally aligned dots) have been considered. In addition, the feasibility of "steering" excitation into superficial nerve trunk regions using subthreshold levels of current flow from an electrode dot located on the opposite side of the nerve has been tested. ⋯ In three acute experiments on cat sciatic nerve the objective was to characterize the effectiveness of each electrode configuration in selectively activating only the medial gastrocnemius muscle. Modeling and experimentation both suggest that longitudinally aligned tripolar dot electrodes on the surface of a nerve trunk, and bounded by a layer of insulation (such as a nerve cuff), will restrict excitation to superficial nerve trunk regions more successfully than will monopolar dot electrodes. Excitation "steering" will improve the spatial selectivity of both monopolar and tripolar electrode configurations.
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IEEE Trans Biomed Eng · Mar 1990
Frequency analysis of the peripheral pulse wave detected in the finger with a photoplethysmograph.
A photoelectric plethysmograph is described that performs a frequency analysis of the peripheral volume pulse wave using a portable computer. It was used to determine how the pulse shape varied with age using 54 subjects in three age groups, 10-29, 30-59, and 60-89 years. The youngest group had a larger power in the second harmonic, (normalized to the fundamental), with p less than 0.05 than the older two groups. The decrease of power in the harmonics of the peripheral pulse wave with age may be a useful noninvasive measure of aging and vascular disease.
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IEEE Trans Biomed Eng · Feb 1990
System for mechanical measurements during cardiopulmonary resuscitation in humans.
Effective study of CPR requires measurement of the mechanical properties of the human chest and the resultant vascular pressures. A computer-based mobile data acquisition system was designed and built for this purpose. During manual CPR a short cylindrical module was placed between the rescuer's hands and the patient's chest. ⋯ An audible signal was produced as an aid in maintaining desired compression rate and duration. The system's mobility permitted rapid implementation at any hospital location. In conclusion, this system was capable of measuring, recording, and displaying multiple physical quantities during manual CPR in humans.