Effects of superior laryngeal nerve lesion and airway protection on kinematics of swallowing in an infant mammal model

Purpose Detailed sensory feedback is essential to facilitate airway protection during the kinematics, or complex movements, of a swallow. The superior laryngeal nerve (SLN) is the trigger for the swallow, and its sensory field is critical for swallow safety. Because of its role in initiating the swallow, we hypothesize that an SLN injury will alter the timing of events. Thus, we determined the effects of a surgical lesion of the SLN on swallow kinematics using an animal model, which permitted extensive VFSS data collection. Methods Under anesthesia, we implanted radio-opaque markers into the posterior tongue, epiglottis, and hyoid bone in three infant pigs. We recorded feeding on milk with barium, while filming at 60fps. We measured three variables shown to be critical: (1) swallow duration, as measured by the time between initial flip of the epiglottis and its return; (2) anterior distance traveled by the hyoid, as well as speed; (3) posterior tongue ratio, which is the ratio of the total pathway traveled by the posterior tongue during the swallow to the pathway traveled only during the posterior flip of the epiglottis. We used the infant mammalian penetration/aspiration scale to quantify airway protection failure. Results There were no treatment (pre- versus post-lesion) effects in any kinematic variable. We found that unsafe swallows (where penetration and/or aspiration occurred) were significantly longer than safe swallows (without penetration or aspiration; p=0.0016). Individual variation was high, showing marginally significant differences among subjects with respect to posterior tongue ratio, swallow duration, and hyoid movements. Conclusions Regardless of sensory deficit, the kinematics of safe swallows did not change. This suggests that the impact of the SLN lesion can change the trigger for a swallow, but that once initiated, the kinematics follow a standard and reflexive pattern. This is different from results for other interventions, such as RLN lesion, which show distinct kinematic accommodations. Learning objective Participants will understand that injury to the superior laryngeal nerve can change the trigger for a swallow, but has little effect on the sequence of events.