The Normal Electromyogram In Human Cricothyroid Muscle

Abstract

The electromyographic pattern in 17 cricothyroid muscles of 13 healthy subjects has been determined. The EMG recordings were made with a concentric needle electrode, recording area 0.03 mm². In the majority of the muscles there was continuous activity during quiet breathing throughout the phases of respiration. Some motor units fired with a steady frequency, whereas in the others the discharge frequency varied with the respiratory phases, some showing an increase during inspiration, others during expiration. Some 20 motor unit potentials were identified from each muscle and, in all, 338 motor unit potentials were analysed. Most of the action potentials were di- or triphasic. Polyphasic potentials occurred in 1% of the total number of potentials. The mean duration of the action potentials was 3.99 ± 1.40 ms. The incidence of potentials ≤ 2 ms in the whole material was 5% and varied in individual muscles between 0 and 16%. The mean amplitude was 394 μV. The 10th and 90th percentiles were 150 μV and 800 μV respectively. The maximal amplitude of the interference pattern during deglutition was usually in the range of 1 200–2 000 μV.