Effect of reference electrode position on the compound muscle action potential (CMAP) onset latency.
Compound muscle action potential (CMAP) onset latency is interpreted to reflect the arrival time at the muscle of impulses in the fastest-conducting motor nerve fiber. However, we have observed that the position of the reference or indifferent electrode (E2) affects CMAP onset latency. Motor nerve conduction studies (NCS) of the median, ulnar, and deep ulnar motor (DUM) nerves on 20 normal hands were performed using both traditional bipolar and experimental monopolar (referenced to the contralateral hand) montages. As the position of E2 was altered, the CMAP onset latency varied 0.1-0.5 ms for the median NCS, 0.1-0.3 ms for the ulnar NCS, and 0.1-1.5 ms for the DUM NCS. This study demonstrates that E2 recorded potentials are significant and vary with positioning, affecting motor onset latency. This has implications both for reference values and the physiologic interpretation of the CMAP waveform.
Medical College of Wisconsin, Zablocki VA Medical Center, Department of Physical Medicine and Rehabilitation, 5000 W. National Avenue, Milwaukee, Wisconsin 53295, USA.
Gulapar
G
Phongsamart
Jacqueline J
JJ
Wertsch
Mohammed
M
Ferdjallah
John C
JC
King
D Terrence
DT
Foster
D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004566:Electrodes; D005260:Female; D006225:Hand; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology; D011930:Reaction Time / Q000502:physiology*; D012016:Reference Values; D014459:Ulnar Nerve / Q000502:physiology