Respiratory functions of the inferior pharyngeal constrictor and sternohyoid muscles during sleep.

We studied the respiratory activity of the inferior pharyngeal constrictor and sternohyoid muscles of the rat during non-rapid eye movement (non-REM) and REM sleep. Each animal carried chronically implanted electrodes for recording the integrated EMG activity of respiratory muscles as well as the electrocorticogram (ECoG) and postural tone (dorsal neck EMG). The latter permitted polygraphic identification of sleep states. Curled up postures enhanced inspiratory activity of both upper airway muscles during non-REM sleep, an effect which CO2 breathing failed to augment except in the well curled up position. Hypoxia reduced their activity. During REM sleep, the inferior pharyngeal constrictor and sternohyoid muscles retained their inspiratory activity. No tonic activity could be detected in either muscle. We conclude that the inferior pharyngeal constrictor and sternohyoid muscles safeguard upper airway patency in the two main sleep states.