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 air way. The fiberoptic scope was advanced through the rostral trachea into the pharynx. Computer-based planimetry was used to measure airway area and max imum anteroposterior and lateral diameters in the rostral oropharynx, velop harynx, and caudal oropharynx. Cuff electrodes stimulated the bilateral dis tal cut ends of the following nerves: medial hypoglossus (MHG), lateral hyp oglossus (LHG), glossopharyngeus, and pharyngeal branch of vagus (PBV). The velopharyngeal area increased with stimulation of the MHG, MHG plus LHG, a nd glossopharyngeus. The velopharyngeal area decreased with PBV stimulation . Similar effects occurred in the caudal oropharynx. The percent increase i n velopharyngeal area with combined MHG and LHG stimulation was greater tha n 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 con centric with the HG stimulations, but glossopharyngeal stimulation resulted in a greater increase in lateral than anteroposterior wall movement. The r esults indicate that the mechanical effects of pharyngeal muscle contractio n depend on the airway level and the specific muscles that are activated.