Effects of pharyngeal muscle activation on airway size and configuration

Fiberoptic imaging was performed in six decerebrate, tracheotomized cats to determine the effect of pharyngeal muscle activation on the pharyngeal airway. The fiberoptic scope was advanced through the rostral trachea into the pharynx. Computer-based planimetry was used to measure airway area and maximum anteroposterior and lateral diameters in the rostral oropharynx, velopharynx, and caudal oropharynx. Cuff electrodes stimulated the bilateral distal cut ends of the following nerves: medial hypoglossus (MHG), lateral hypoglossus (LHG), glossopharyngeus, and pharyngeal branch of vagus (PBV). The velopharyngeal area increased with stimulation of the MHG, MHG plus LHG, and glossopharyngeus. The velopharyngeal area decreased with PBV stimulation. Similar effects occurred in the caudal oropharynx. The percent increase in velopharyngeal area with combined MHG and LHG stimulation was greater than the sum of the increases stimulating either branch alone. In the rostral oropharynx, airway area increased with individual and combined stimulation of the MHG and LHG. Changes in airway area at the different levels were concentric with the HG stimulations, but glossopharyngeal stimulation resulted in a greater increase in lateral than anteroposterior wall movement. The results indicate that the mechanical effects of pharyngeal muscle contraction depend on the airway level and the specific muscles that are activated.