Transcutaneous electrical stimulation of the recurrent laryngeal nerve: a method of controlling vocal cord position

This study was designed to examine the feasibility of transcutaneous stimulation of the recurrent laryngeal nerve. Electrical activation of the recurrent laryngeal nerve was achieved by applying a blunt electrode to the intact neck skin at specific points along the tracheoesophageal groove in anesthetized adult dogs. The stimulus consisted of 10 mA cathodal pulses, each of 1 msec duration, delivered at a frequency of 10 Hz and increased by 10 Hz increments up to 100 Hz. Vocal cord excursion was directly related to the frequency of applied current. In all six dogs studies, stimulation at 30 Hz resulted in maximal ipsilateral vocal cord abduction, while stimulation at frequencies greater than 40 Hz resulted in ipsilateral vocal cord adduction up to or across the midline. Vocal cord movement was immediate and persisted for the duration of the stimulus train. Surrounding neck muscles were not visibly activated. We propose that the observed frequency-dependent movement of the vocal cords occurred because of the difference between the contraction times of the intrinsic abductor and adductor muscles of the larynx. Transcutaneous recurrent laryngeal nerve stimulation appears promising, both as a diagnostic aid in laryngoscopy and as a therapeutic tool in controlling the glottic aperture.