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KMID : 0861220100120010011
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Journal of the Korean Society Clinical Neurophysiology
2010 Volume.12 No. 1 p.11 ~ p.15
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The Influence of the Reference Electrode on Compound Muscle Action Potential Onset Latency and Amplitude
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Lee Sang-Moo
Sohn Jong-Hee
Choi Hui-Chul
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Abstract
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Background: In belly-tendon (bipolar) montage, reference (R2) electrode placed on muscle’s tendon has traditionally been considered to be electrically inactive. However, recent studies have revealed that R2 electrode is not simply referential, but actively contributes to compound muscle action potential (CMAP) waveform morphology. These findings suggest that CMAP onset latency and amplitude may also be influenced by the position of R2 electrode. This study was performed in order to evaluate the effect of R2 electrode position on CMAP onset latency and amplitude.
Methods: We performed motor nerve conduction studies of median, ulnar, tibial and peroneal nerves on bilateral limbs of 20 normal subjects. We used traditional bipolar and monopolar montage and compared their CMAP onset latencies and amplitudes. In bipolar montage, recording (R1) electrode was placed on mid-belly of muscle with R2 electrode on the tendon of the muscle. In monopolar montage, R1 electrode was placed on the same site of bipolar montage, while R2 electrode was placed on the contralateral limb.
Results:The mean CMAP onset latencies of median and peroneal nerves in bipolar montage were significantly different (p<0.05) with those in monopolar montage. And those of ulnar and tibial nerves were not significantly different (p>0.05). The mean CMAP amplitudes of all the tested nerves except ulnar nerve were significantly different (p<0.05).
Conclusions : This study shows that change in R2 electrode position can affect the CMAP onset latency and amplitude, and these differences seem to be related to the generation of far field potential by CMAP.
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KEYWORD
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Compound muscle action potential, Onset latenc, Reference electrode
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