Thyroarytenoid muscle activity during wakefulness and sleep in normal adults.

To determine the respiratory-related activity of the thyroarytenoid (TA) muscle in normal adults, intramuscular electromyographic recordings were performed in eight normal adult males during wakefulness and sleep. Phasic expiratory TA activity was present during normal tidal breathing in all subjects during wakefulness. Tonic activity was frequently present during inspiration. After an initial rapid rise in activity near the onset of expiration, phasic TA activity generally exhibited one of three different discharge patterns: a plateau, a progressive increase, or, less commonly, a progressive decrease in activity. In four of five subjects examined, peak TA activity during quiet breathing in wakefulness appeared to be directly related to time of expiration. At a particular lung volume above end-expiratory volume during wakefulness, measurements of expiratory resistance were directly related to the level of TA activity. TA activity disappeared during stable periods of non-rapid-eye-movement sleep and exhibited paroxysmal bursts of activity during rapid-eye-movement sleep. The results during wakefulness indicate that the TA contributes to an active adduction of the vocal cords in expiration and suggest the presence of an active laryngeal braking mechanism during exhalation.