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UBC Theses and Dissertations

Recording properties of a concentric needle electrode for electromyography as measured in an electrolytic tank model Sutter, Martin


The widely used concentric needle electrode produces electromyograms that do not exactly correspond to the true signal in the muscle. The presence of the electrode induces distortions of the original field distribution in the muscle, and the cannula does not act as a perfect reference electrode of zero voltage. In order to assess the signal distorting properties, which have not been numerically established, an experimental- investigation was carried out. A dipole generator in an electrolytic tank was employed to model a single muscle fiber as well as a motor unit equivalent. The potential field was mapped with a point-shaped electrode so that the "true" field distribution as a basis for comparisons was established. Three sub-assemblies and a complete model concentric needle electrode were separately available for measurements. The field distorting properties of the core, the insulator surrounding the core and the cannula, were experimentally quantified. The cannula potential was determined as a function of the insertion depth and as a function of the spatial arrangement of a nearby single fiber or a motor unit. The overall distortions introduced by the concentric needle electrode were measured for both single fiber and motor unit potentials. Finally, with the knowledge gained in the investigation, a new concentric needle electrode was designed and tested which evinced substantial improvements in its recording fidelity compared to the conventional design.

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