Objective: To quantitatively analyze and explore the characteristics, influencing factors, reference value range, and variability of electromyography and nerve evoked potential in normal laryngeal muscles.
Methods: The study included 480 patients diagnosed with unilateral vocal fold paralysis and underwent laryngeal electromyography (LEMG) at our hospital from June 2012 to June 2022, including 259 males and 221 females, with an average age of 44.44±14.91years. Characteristics of the motor unit potential (MUP), recruitment pattern, and evoked potential in the thyroarytenoid muscle (TA), the posterior cricoarytenoid muscle (PCA) and the cricothyroid muscle (CT) of the normal side were analyzed, with the coefficient of variation (CV), reference value range of each parameter, and differences in different genders and age groups analyzed simultaneously.
Results: The amplitudes of MUP in TA, PCA, and CT muscles were 129.52±24.95_V, 240.67±88.25_V, and 125.88±21.36_V, respectively. The durations were 3.67±0.17ms, 3.82±0.29ms and 3.68±0.17ms, respectively. The numbers of MUP phase were 1.94±0.28, 2.16±0.38, and 1.98±0.25, respectively. The numbers of turns in TA, PCA, and CT muscles were 565.76±193.88/s, 520.94±170.99/s, and 523.29±159.58/s, respectively. The amplitudes of the recruitment pattern were 1038.00±368.65_V, 1269.91±434.75_V, and 919.64±240.54_V, respectively. The latencies of laryngeal nerve evoked potentials in TA, PCA, and CT muscles were 1.69±0.08ms, 1.70±0.08ms, and 1.70±0.11ms, with durations of 6.20±1.30ms, 6.41±1.34ms, and 7.05±1.67ms, respectively. The amplitudes were 7.42±3.62mV, 6.05±2.83mV, and 5.54±2.62mV, respectively. The durations of MUP in male laryngeal muscles was higher than that in females, with statistical differences in TA (P<0.01) and CT (P<0.05) muscles, and the durations of evoked potentials was higher than that in females (P<0.01). The duration of PCA evoked potentials was weakly negatively correlated with age (r= – 0.17, P<0.01). The reference ranges for MUP duration in TA, PCA, and CT muscles were 3.30-3.90ms, 3.40-4.30ms, and 3.30-3.90ms, respectively, and the latencies of the evoked potential were concentrated at 1.70ms, the CVs of whom were all less than 10%.
Conclusions: This study analyzed the parameters of MUP, recruitment pattern, and evoked potential in laryngeal muscles of the normal side, as well as the normal reference range. Among them, the duration of MUP and the latency of evoked potential are relatively small, which can be used as characteristic indicators for normal laryngeal muscles and nerves. MUP of TA and CT muscles in male patients, as well as the duration of all the evoked potentials, are higher than those in females, and the trend of changes in the parameters with age is not significant.