Regional effects of selective pharyngeal muscle activation on airway shape

Pharyngeal airway fiberoptic imaging was performed in 10 decerebrate cats to determine the effect of selective pharyngeal muscle activation on airway shape. At intraluminal pressures from 6 to -6 cm H2O, maximum anteroposterior and lateral diameters were measured in the rostral oropharynx, caudal oropharynx, and velopharynx with and without bilateral stimulation of the medial hypoglossus (HG), lateral HG, whole HG, glossopharyngeus, and pharyngeal branch of vagus nerves. At all three airway levels without nerve stimulation, the increase in diameter with increasing pressure was greater in the lateral than anteroposterior dimension. Stimulation of the hypoglossal and glossopharyngeus nerves caused greater increases in lateral than anteroposterior diameter in all three regions with different effects across nerves and regions. Stimulation of these four nerves frequently caused greater increases in both diameters, as the airway cross-sectional area was decreased by lowering airway pressure. Stimulation of the pharyngeal branch of vagus resulted in greater decreases in lateral than anteroposterior dimension in the caudal oropharynx and velopharynx, especially as airway cross-sectional area was increased by increasing intraluminal pressure. The results indicate that selective activation of pharyngeal muscles in cats frequently results in greater changes in lateral than anteroposterior airway diameter and that these effects are dependent on airway region and cross-sectional area.