Accelerometer-based characteristics of evoked mechanomyograms in the orbicularis oculi muscle

Electromyograms (EMGs) of the orbicularis oculi muscle are commonly used to assess the blink reflex, which provides clinically important information. However, mechanomyograms (MMGs) may serve as a promising alternative. This study aimed to evaluate the utility of MMGs in assessing orbicularis oculi responses to stimulation. Electrical stimulation was applied to the facial nerve axons of 25 healthy adult participants, and MMGs were recorded using an accelerometer. The reliability of amplitude-based parameters (Amax and Ap−p) and time-based parameters (Trise, Tzero, Tfall, and Trec) characterizing MMG waveforms was assessed using the intraclass correlation coefficient (ICC), standard error of measurement (SEM), and coefficient of variation (CV). Additionally, the amplitude and temporal characteristics of MMGs evoked by varying stimulus intensities were compared with simultaneously recorded EMGs. All parameters, except Trec, showed high relative reliability (95% confidence interval of ICC of > 0.75) and high absolute reliability (%SEM and CV < 10%). MMG amplitudes (Amax and Ap−p) and EMG amplitudes (Vmax and Vp−p) increased linearly with stimulus intensity. A strong correlation was found between the amplitudes of both signals (Vmax vs. Amax: r = 0.932, p < 0.0001; Vp−p vs. Ap−p: r = 0.937, p < 0.0001). The first positive MMG peak consistently appeared at a fixed interval (5.52 ± 2.10 ms) after the EMG peak, irrespective of stimulus level. These findings suggest that MMG amplitude and latency (stimulus-to-peak time) are reliable indicators of orbicularis oculi muscle activity and can be effectively used alongside EMG in clinical and research settings. Communicated by Bill Yates.