Surface Electromyography for Identification of Pre-Phonatory Activity

Surface electrode EMG is an established method for studying biomechanical activity. It has not been well studied in detecting laryngeal biomechanical activity of pre-phonatory onset. Our aims were to compare the sensitivity of surface EMG in identifying pre-phonatory laryngeal activity to needle electrode laryngeal EMG and to compare the pre-phonatory period in patients with adductor laryngeal dystonia (ADLD) with that in controls. ADLD patients (n = 10) undergoing needle LEMG prior to Botox injection and participants with normal voices (n = 6) were recruited. Surface EMG electrodes were placed over the cricoid ring and thyrohyoid membrane. Needle EMG electrodes were inserted into the thyroarytenoid muscle. EMG and auditory output samples were collected during phonation onset. Tracings were de-identified and evaluated. Measurements of time from onset in change of the amplitude and motor unit frequency on the interference pattern to onset of phonation were calculated by two blinded raters. 42 of 71 patient and 40 of 50 control tracings were available for analysis. Correlation for pre-phonatory time between electrode configuration was 0.70 for patients, 0.64 for controls and 0.79 for all the data combined. Inter-rater correlation was 0.97 for needle and 0.96 for surface electrodes. ADLD patients had a longer pre-phonatory time than control subjects by 169.48ms with surface electrode and 140.23ms with needle electrode (p < 0.001). Surface EMG demonstrates equal reliability as Needle EMG in detecting pre-phonatory activity in controls and subjects. Patients with ADLD have a significantly prolonged pre-phonatory period when compared with controls.

Respiration-Related Laryngeal Electromyography in Children with Bilateral Vocal Fold Paralysis

We present 2 case reports to demonstrate the relationship between laryngeal muscle activity and respiration in children with bilateral vocal fold paralysis (BVFP) by simultaneous laryngeal electromyography (EMG) with recording of chest wall movement and intercostal muscle EMG. Laryngeal EMG was performed together with recording of chest wall movement in a 55-day-old girl who was undergoing tracheostomy for idiopathic congenital BVFP. Normal phasic activity was observed, ie, the thyroarytenoid (TA) muscle was active during expiration and the posterior cricoarytenoid (PCA) muscle during inspiration, suggesting a good prognosis for recovery. The child was decannulated at 11 months. Laryngeal EMG together with recording of chest wall movement and intercostal EMG in a 5-year-old girl who was tracheostomy-dependent following tracheoesophageal fistula repair due to BVFP showed phasic activity during expiration for both the TA and PCA muscles, indicating aberrant regeneration of the PCA motor nerve. The timing of laryngeal muscle activity with respiration in the assessment of pediatric congenital BVFP is essential to demonstrate the presence of normal or abnormal medullary respiratory neuronal input to laryngeal motoneurons. In cases in which BVFP is due to recurrent laryngeal nerve injury, respiration-related laryngeal EMG will identify aberrant regeneration. Laryngeal EMG should be combined with intercostal muscle EMG in the evaluation of children with significant vocal fold dysfunction of either central or peripheral origin.