The Role of Palatal Sensation during Sucking and Pharyngeal Swallowing in the Infant Pig

Abstract

Swallowing dysfunction in infants can be caused by differences in craniofacial anatomy, neurological disorders or prematurity. These conditions result in difficulty initiating pharyngeal swallow cycles and/or a lack of airway protection during the swallow that can result in aspiration. In order to provide swallowing rehabilitation for these infants, we need to know more about the sensory and motor interactions that occur during the normal infant swallow. The overall aim of this dissertation was to understand how reducing palatal sensation would affect the oral and pharyngeal phase of the swallow. We hypothesized that after a palatal injection of local anesthesia both phases would show significant changes in movements of the tongue, hyoid and epiglottis that may result in less airway protection during the pharyngeal swallow. We also hypothesized we would observe changes in muscle activity to explain the mechanism of the altered kinematics. We used an infant pig model of mammalian feeding to test these hypotheses. Electromyographic (EMG) electrodes were implanted into several hyoid and pharyngeal muscles. We fed the pigs while simultaneously recording EMG and lateral videofluoroscopy captured at 60 frames per second. We evaluated these recordings during feeding sessions with no treatments and compared them to feeding sessions following a palatal anesthesia (0.5% bupivacaine hydrochloride) or saline injection. In order to evaluate airway protection before and after the treatments, we developed the infant mammalian penetration-aspiration scale (IMPAS). A novel method was developed to test local anesthesia duration in infants that proved bupivacaine hydrochloride lasted at least one hour after injection before the return of oral reflexes. Using these methods, we demonstrated that reducing palatal sensation has profound effects on frequency, kinematics and motor function during the oral and pharyngeal swallow. Preliminary data suggests that the infant pharyngeal swallow may also be capable of motor learning. These studies demonstrate an important role for trigeminal sensation in the normal initiation and coordination of the sucking and swallowing CPGs in the brainstem. Future studies are needed to determine if manipulating oral sensory receptors can lead to novel dysphagia rehabilitation strategies in human patients.