Effects of pharyngeal muscle activation on airway pressure-area relationships

Fiberoptic imaging in an isolated, sealed upper airway was performed in 10 decerebrate cats to determine the effect of pharyngeal muscle activation on airway pressure-area relationships. Bilateral cuff electrodes stimulated the distal cut ends of the following nerves: medial and lateral hypoglossus, glossopharyngeus, and pharyngeal branch of vagus. At given intraluminal pressures ranging from +6 to -6 cm H2O, cross-sectional area was measured in the rostral oropharynx, velopharynx, and caudal oropharynx, with and without nerve stimulation. A mixed model analysis of variance indicated a relatively constant increase in area across the pressure range with glossopharyngeal stimulation at any given level. Significant interactions between pressure and stimulation were present in the rostral oropharynx with medial hypoglossus stimulation and in the caudal oropharynx with independent and combined hypoglossal branch stimulation and pharyngeal branch of vagus stimulation. With stimulation of the hypoglossal nerves, greater increases in area in these regions occurred in the lower pressure ranges. Stimulation of the pharyngeal branch of the vagus caused a greater decrease in area at the higher pressure ranges in the caudal oropharynx and velopharynx. The results indicate that the mechanical effects of pharyngeal muscle activation depend not only on the region and muscles activated but also on the intraluminal pressure.