OBJECTIVETo study the behaviors of normal recurrent laryngeal nerve and superior laryngeal nerve evoked electromyography, to know the reference values of related parameters.

METHODSThirty six normal subjects were studied with laryngeal evoked electromyography. The latent period, duration, and amplitude of the evoked potentials (EP) recorded in laryngeal muscles were investigated.

RESULTSThe latent period of the EP recording from the thyroarytenoid muscles (TA), after stimulating recurrent laryngeal nerve (RLN), was (1.13 - 2.25) ms (x +/- 2s), that of TA after stimulating vagus nerve (VN) was (2.57 - 5.85) ms. There were significant differences in the latent periods of EP between RLN and VN (P < 0.01), and the latent periods of EP recording from TA after stimulating right cervical part of VN, (2.01 - 4. 53) ms (x +/- 2s) were significant shorter than those of left, (3.70 - 6.98) ms (x +/- 2s, P < 0.01). The durations of the EP were somewhat different but not significant. The amplitudes of the EP in different laryngeal muscles changes markedly. The wave form and latent period of the EP recording from cricothyroid muscle (CT), after stimulating the external branch of superior laryngeal nerve (SLN), was similar with the EP of RLN, the reflective EP R1 and R2 could be recorded from TA, posterior cricoarytenoid muscles (PCA), CT after stimulating the internal branch of SLN.

CONCLUSIONSThe characteristics of the EP recorded in laryngeal muscles after stimulation of RLN, SLN and VN are different. The latent period, duration and amplitude are important parameters in the evaluation of laryngeal nerves function, the latent period is the most important parameter.