一側内耳麻酔前後における頸筋筋電図学的検討

抄録

The vestibulo-collic system senses the head position and movements three-dimen-sionally in space. In turn, it initiates activity in neck muscles that maintain an adequate head position to stabilize the angle of gaze.
Surface electromyography (EMG) of neck muscles were recorded to determine responses of the vestibulo-collic system after acute, transient unilateral vestibular impairment resulted from the lidocaine anesthesia of the inner ear as a therapy for tinnitus. Nineteen patients treated by such therapy underwent recording before/after unilateral anesthesia. EMG recordings were obtained using surface electrodes on the sternocleidomastoid (SCM) and splenius (Sp) muscles in a lateral reclining position with the anesthetized ear upward. There were no remarkable changes in surface EMG activity of neck muscles in 3 normal subjects between supine and lateral positions before anesthesia. After anesthesia, EMG activity in the ipsilateral SCM was significantly increasing for 4-6 hours, while there were no remarkable changes in the contralateral SCM or the Sp on either side.
Electrophysiological studies demonstrate that SCM motoneurons receive disynaptic excitatory inputs from contralateral vestibular canals and disynaptic inhibitory inputs from ipsilateral canals through the medial vestibulospinal tract (MVST). Taken together, results from this study suggest that increasing EMG activity of the ipsi-SCM could result from "disinhibition" of the inhibitory pathway from the ipsilateral, transiently suppressed vestibular activity due to inner ear local anesthesia.