Thyroarytenoid muscle activity in sleep apneas

In normal subjects the thyroarytenoid muscle (TA), a vocal cord adductor, has phasic expiratory activity during wakefulness that disappears during non-rapid-eye-movement (NREM) sleep. Fiber-optic studies have reported absent or irregular vocal cord movements during obstructive apneas and vocal cord adduction during central apneas. This study was designed to investigate TA activity during NREM sleep in 14 subjects with sleep apnea by means of intramuscular wire electrodes. During central apneas, which were recorded in three subjects, continuous TA activity was observed. During obstructive apneas, which were recorded in all subjects, two different patterns of TA activity were observed: 1) absence of any activity until arousal and 2) phasic activity throughout the apnea. The first pattern was detected in six subjects, whereas both patterns were observed in the remaining eight subjects. No correlation was found between obstructive apnea characteristics and presence or absence of TA activity. In all subjects TA underwent a marked activation during arousal. While nasal continuous positive airway pressure was applied during NREM sleep TA activity was always absent. The persistence of TA activity during central apneas suggests that they may represent an extreme prolongation of neural expiratory discharge. We speculate that a variable interaction of different stimuli acting during obstructive apnea may activate TA, which, in turn, may contribute to glottic narrowing.