Respiratory-related control of palatoglossus and levator palatini muscle activity

Route of respiration [nasal (NR) vs. oral (OR)] is determined by the position of the soft palate. Despite this, little is known about the respiratory-related activity of palatal muscles. We investigated the activity of two palatal muscles: palatoglossus (PG) and levator palatini (LP). Eight normal male subjects were studied during wakefulness with intramuscular electrodes placed in the PG and LP. The electromyograms (EMGs) of the PG and LP were measured during both NR and OR under 1) quiet basal respiration, 2) inspiratory resistive loading (25 cmH2O.l-1.s), and 3) progressive hypercapnia. The PG consistently demonstrated inspiratory phasic activity during NR with greater inspiratory and expiratory EMGs (P < 0.05) during basal NR compared with basal OR [3.3 +/- 0.2 (SE), 1.1 +/- 0.1, 2.3 +/- 0.4, and 1.0 +/- 0.2 arbitrary units for PG nasal inspiratory, PG oral inspiratory, PG nasal expiratory, and PG oral expiratory, respectively]. During OR, the LP was inspiratory phasic in 4 subjects and expiratory phasic in 4 subjects, with greater inspiratory and expiratory EMGs during basal OR compared with basal NR (5.5 +/- 1.1, 2.1 +/- 0.4, 6.8 +/- 1.5, and 1.8 +/- 0.4 arbitrary units for LP oral inspiratory, LP nasal inspiratory, PG oral expiratory, and PG nasal expiratory, respectively). Both muscles demonstrated significantly increased activity during both inspiratory resistive loading and hypercapnia. However, their route-specific activation pattern continued during such stimulated breathing. We conclude that 1) the route of respiration is influenced by the complex interaction of the PG and LP and 2) the response of these muscles to respiratory stimuli is dependent on the route of respiration.