On the optimal choice of a recording electrode in electroneurography

The influence of the type and size of recording electrodes on compound nerve action potentials was studied in order to establish optimal prerequisites for the application of quantitative analysis methods. A realistic volume conductor model was used to assess the dependence of the recorded signal on the position of the recording electrode with respect to the nerve. The analysis of both compound action potentials (CAPs) and single fibre action potentials (SFAPs) leads to the conclusion that near-nerve recording gives substantially more information. This applies in particular to the fine details in the CAP, such as notches in the main complex and the so-called late components. Subsequently, the influence of needle electrode bare tip length on the recorded signal was investigated by spatially averaging the potentials over the lead-off area. These results were combined with experimentally obtained noise levels for different stainless steel needle electrodes in order to determine the signal-to-noise ratio as a function of bare tip length. It was concluded that for near-nerve recording a needle tip of 1-2 mm gives optimal results in terms of wave shape preservation and signal-to-noise ratio.