The effect of magnetic coil orientation on the excitation of the median nerve.
OBJECTIVE
We investigated the effect of magnetic coil orientation on the excitation of the median nerve in healthy subjects.


METHODS
An 8-shaped coil, 3.2 cm in outer diameter, was used. The median nerve was stimulated at the elbow while the compound muscle action potentials (CMAPs) of abductor pollicis brevis muscle were recorded at 4 different directions of the induced current: orthodromic, antidromic, medio-lateral and latero-medial.


RESULTS
We found that the amplitude of the CMAP was the greatest in a medio-lateral (ML) direction. We also measured the induced electric field in the saline tank that mimicked the forearm. The induced electric field and its spatial gradient were the greatest in the ML direction among 4 directions.


CONCLUSIONS
The fact that the forearm is a restrictive volume conductor may result in the different effects of coil orientation on the excitation of the median nerve at the elbow.
Sun
S J
SJ
Department of Clinical Neurophysiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Tobimatsu
S
S
Kato
M
M
D000200:Action Potentials / Q000528:radiation effects; D000328:Adult; D000704:Analysis of Variance; D001132:Arm / Q000033:anatomy & histology / Q000528:radiation effects; D004553:Electric Conductivity; D004558:Electric Stimulation; D004574:Electromagnetic Fields; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000528:radiation effects*; D008959:Models, Neurological; D009431:Neural Conduction / Q000502:physiology*; D010812:Physical Stimulation / Q000379:methods