Soft palate muscle responses to negative upper airway pressure

The afferent pathways and upper airway receptor locations involved in negat ive upper airway pressure (NUAP) augmentation of soft palate muscle activit y have not been defined. We studied the electromyographic (EMG) response to NUAP for the palatinus, tensor veli palatini, and levator veli palatini mu scles in 11 adult, supine, tracheostomized, anesthetized dogs. NUAP was app lied to the nasal or laryngeal end of the isolated upper airway in six dogs and to four to six serial upper airway sites from the nasal cavity to the subglottis in five dogs. When NUAP was applied at the larynx, peak inspirat ory EMG activity for the palatinus and tensor increased significantly (P < 0.05) and plateaued at a NUAP of -10 cmH(2)O. Laryngeal NUAP failed to incr ease levator activity consistently. Nasal NUAP did not increase EMG activit y for any muscle. Consistent NUAP reflex recruitment of soft palate muscle activity only occurred when the larynx was exposed to the stimulus and, fur thermore, was abolished by bilateral section of the internal branches of th e superior laryngeal nerves. We conclude that soft palate muscle activity m ay be selectively modulated by afferent activity originating in the larynge al and hypopharyngeal airway.