[Quantitative analysis on characteristics of electromyography and evoked potential in normal laryngeal muscles]

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 immobility and underwent laryngeal electromyography (LEMG) at Beijing Tongren Hospital from June 2012 to June 2022, including 259 males and 221 females, with an average age of (44.4±14.9) years. 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. SPSS 24.0 software was used to analyze the data. Results: The amplitudes of MUP in TA, PCA, and CT muscles were (129.52±24.95) μV, (240.67±88.25) μV, and (125.88±21.36) μV, respectively. The durations were (3.67±0.17) ms, (3.82±0.29) ms and (3.68±0.17) ms, respectively. The numbers of MUP phase were 1.94±0.28, 2.16±0.38, and 1.98±0.25, respectively. The per second numbers of turns in TA, PCA, and CT muscles were 565.76±193.88, 520.94±170.99, and 523.29±159.58, respectively. The amplitudes of the recruitment pattern were (1 038.00±368.65) μV, (1 269.91±434.75) μV, and (919.64±240.54) μV, respectively. The latencies of laryngeal nerve evoked potentials in TA, PCA, and CT muscles were (1.69±0.08) ms, (1.70±0.08) ms, and (1.70±0.11) ms, with durations of (6.20±1.30) ms, (6.41±1.34) ms, and (7.05±1.67) ms, respectively. The amplitudes were (7.42±3.62) mV, (6.05±2.83) mV, and (5.54±2.62) mV, respectively. The duration of MUP in male laryngeal muscles was higher than that in females, with statistical differences in TA (t=5.70, P<0.01) and CT (t=2.41, P<0.05) muscles, and the duration of evoked potentials was higher than that in females (TA: t=3.63; PCA: t=3.21; CT: t=2.98; all 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 (3.30-3.90) ms, (3.40-4.30) ms, and (3.30-3.90) ms, respectively, and the latencies of the evoked potential were concentrated at 1.70 ms, the CVs were all less than 10%. Conclusions: This study analyzes the parameters of MUP, recruitment pattern, and evoked potential in laryngeal muscles of the normal side in patients with unilateral vocal fold immobility, 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.