Meeting Abstract
The mammalian swallow is a complex reflex where the airway must be protected while passing a food bolus into the esophagus. Because of the evolutionary and embryological history of the pharynx, the functions of nerves are less than straight-forward. Although a swallowed bolus does not enter the sensory field of the recurrent laryngeal nerve, absence of this signal produces a dysfunctional swallow, with food or liquid entering the airway. We sought to determine the role of this sensory signal in determining the kinematics of a swallow. We put radio-opaque markers in the tongue, hyoid, thyroid, and epiglottis. We lesioned this nerve in 6 infant pigs, and recorded 60 swallows pre-lesion and 60 swallows post-lesion using digital videofluroscopy at 100 fps in a paired design. Post lesion, animals were able to swallow, but they aspirated milk into their airway frequently. Significant post-lesion differences in swallowing included a longer duration of the swallow and less between-cycle variation in movement. The epiglottis, hyoid, and thyroid had larger excursions of movement. There also were pre and post lesion differences in relative timing and extent of movement in the tongue, which is not directly involved in the mechanics of a swallow. These results suggest that reduced sensation changed the kinematics of the swallow so that the airway was inconsistently protected while liquid passed into the esophagus. The post-lesion slowness and greater magnitude of movements suggest that the swallowing reflex must adjust to accommodate the reduced sensory caudal to the larynx. Furthermore, the changes in movements of all structures, including the tongue, indicate a high level of brainstem coordination among at least five cranial nerves.
