Einfluß der Amplitudenschwelle auf die Parameter der Turns/Amplituden-Analyse

Abstract

In this study we examined the relationship between the amplitude threshold used for the determination of the turns of the electromyographic interference pattern and the classical parameters of the turns/amplitude analysis: mean amplitude and number of turns per second. We investigated whether the choice of an appropriate amplitude threshold could help to discriminate better between myopathic and neuropathic muscles on the one hand and normal muscles on the other. In 16 patients with myopathies, 33 patients with neuropathies and 59 controls the interference patterns of the tibialis anterior muscle were recorded using concentric needle electrodes. Analysis was performed via a computer programme, systematically varying the amplitude threshold between 10 μV and 200 μV. Amplitudes as well as the number of turns per second showed a non-linear relation with the amplitude threshold. By reducing the amplitude threshold to 20 μV we obtained a clearly better separation of the distributions of the number of turns of myopathic, neuropathic and normal EMG, compared to the traditional threshold value of 100 μV. The reduction of the amplitude threshold had no effect on the distributions of amplitude values. The Kolmogoroff-Smirnov distance between the turns parameter distributions of myopathic patients and controls as well as between the distributions of neuropathic patients and controls increased with decreasing amplitude threshold values until a maximum at a threshold value of 20 μV. Hence, for the turns/amplitude analysis of the tibialis anterior muscle it is better to reduce the amplitude threshold to 20 μV.