IEEE transactions on bio-medical engineering
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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.