All recorded potentials during electrophysiologic study are complex signals made of a broad range of frequency subcomponents. The signal's power at each frequency determines the impact of that frequency subcomponent, and these subcomponeents
summate to
produce the wave form seen on the oscilloscope. Electronic filtering is performed to improve the visual quality of the oscilloscope tracing and to reduce the effects of outside and inside interference. But the filter settings are infrequently
reported
so far.
This study was made to investigate a proper filter setting by testing the frequency parameters of peak frequency, band width frequency, and power spectrum density of the electronic signals in normal surface electromyography and motor and sensory
conduction studies. There was no significant signal frequency above 1,000 Hz recorded in the surface electromyography and motor nerve conduction study and above 2,000 Hz in the sensory nerve conduction study. A frequency range from 1~2 Hz(low
frequency)
to 10,000 Hz(High frequency) for recording of motor unit action potential and compound muscle action potential provides sufficient in reproduction of most potentials. Adjusting filter setting of 1~2 Hz(low frequency) and 2,000~4,000 Hz(high
frequency)
in the sensory nerve conduction study can minimize an effect by the 60 Hz noise and the internal noise extending over a wide spectrum of frequencies of the signals having very low power and amplitude. Base line shift could be minimized by
increasing the
low filter setting from 1~2 Hz to 10 or 20 Hz if any.
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