Meeting Abstract
Swallowing is an important and complex activity, requiring precise coordination between sensory fields, muscles, and bony and cartilaginous structures. When mammals swallow, coordinated muscles move the hyoid bone anteriorly and dorsally. This movement, which occurs just before or early during the swallow, is one way that the airway is protected from penetration by or aspiration of a bolus. Furthermore, the hyoid movement opens the esophagus, lowering the air pressure and drawing the bolus into it. We examined the kinematics of the hyoid in nine infant pigs. Animals drank milk mixed with contrast agent while fluoroscopy allowed visualization of hyoid position and movement. Then, during aseptic surgery, we located and transected either the right-side superior laryngeal nerve or recurrent laryngeal nerve. We digitized the hyoid and other structures, and also scored the extent to which the airway was protected from bolus penetration or aspiration. The effect of nerve transection on the distance traveled by the hyoid was significant (p=0.01). However, the effects were different between the superior laryngeal and recurrent laryngeal nerves. Hyoid speed was not affected by any treatments. Airway protection was worse after the nerve transection, regardless of which type. However, hyoid travel distance or speed did not differ with airway safety. We conclude that protection of the airway is a multifaceted phenomenon, and that other factors such as bolus velocity and closure of laryngeal valves are also important. Control of hyoid movement is influenced by multiple nerves, either directly through innervation of muscles that attached to the hyoid, or indirectly via vagus and other cranial nerves that interconnect in the brainstem.
