We have recently demonstrated that measurements of the magnetic field outside a nerve can be used readily for quantitative determination of current flow within a nerve. There are a large number of problems in both basic and clinical reserch that could be addressed by this technique. Surgically-exposed nerves are studied acutely to assess the level of injury of a traumatized peripheral nerve. These techniques are limited by the need to lift the nerve with hook electrodes and dry it off. Magnetic techniques would allow measurement of the nerve lying in its own tissue bed while immersed in saline and should reduce risk of damage to the nerve. The magnetic measurement of current without assumptions regarding resistivities may improve quantitative assessment of nerve injury. Chronically implanted electrodes can be used to control a prosthetic device or to monitor the regeneration of a nerve. The performance of implanted stimulating and recording electrodes is limited by electrochemical effects at the electrode-tissue interface. Inductively-coupled toroids offer the advantage of not having tissue-to-metallic electrode interfaces that are subject to degradation with time. Compared to electrical techniques, stimulus artifacts may prove to be less of a problem with inductive stimulation and recording since there is no capacitive charge storage at high-impedance electrode-tissue interfaces and since artifact cancelling currents can be readily induced in the recording toroid. Basic research into the nature of cell-to-cell currents in hampered by the inability to make direct electrical measurements of intracellular and intercellular currents without detailed assumptions regarding resistivities. Magnetic techniques overcome this. We propose to determine whether magnetic measurements of axial currents in nerves can eliminate some of the practical and fundamental problems of electrical measurements. The proposed research will include in vitro and in vivo experiments to define the merits of magnetic assessment of conduction in bundled nerves, studies of current propagation in septated nerves, and exploration of nerve stimulation using toroidal transformers. Successful completion of this research may result in the development of new clinical tools and the extension of our understanding of cellular action currents in multi-cell systems.
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