Pre-pharyngeal Swallow Effects of Recurrent Laryngeal Nerve Lesion on Bolus Shape and Airway Protection in an Infant Pig Model

Abstract

Recurrent laryngeal nerve (RLN) damage in infants leads to increased dysphagia and aspiration pneumonia. Recent work has shown that intra oral transport and swallow kinematics change following RLN lesion, suggesting potential changes in bolus formation prior to the swallow. In this study we used geometric morphometrics to understand the effect of bolus shape on penetration and aspiration in infants with and without RLN lesion. We hypothesized 1) that geometric bolus properties are related to airway protection outcomes and 2) that in infants with RLN lesion, the relationship between geometric bolus properties and dysphagia is changed. In five infant pigs, dysphagia in 188 swallows was assessed using the Infant Mammalian Penetration Aspiration Score (IMPAS). Using images from high-speed VFSS, bolus shape, bolus area, and tongue outline were quantified digitally. Bolus shape was analyzed using elliptical Fourier analysis, and tongue outline using polynomial curve fitting. Despite large inter-individual differences, significant within individual effects of bolus shape and bolus area on airway protection exist. The relationship between penetration-aspiration score and both bolus area and shape changed post lesion. Tongue shape differed between pre and post lesion swallows, and between swallows with different IMPAS scores. Bolus shape and area affect airway protection outcomes. RLN lesion changes that relationship, indicating that proper bolus formation and control by the tongue requires intact laryngeal sensation. The impact of RLN lesion on dysphagia is pervasive.

Specific Vagus Nerve Lesion Have Distinctive Physiologic Mechanisms of Dysphagia

“…The results of this study show that similar patterns to what is found with bolus size also apply to swallowing mechanics and kinematics, namely movement of the posterior tongue and duration of epiglottal inversion. Our results agree with previous studies that documented that RLN and SLN lesion affected bolus size differently (13,19). Furthermore, how all these swallow parameters relate to airway protection deficits after lesion of either nerve also differs, indicating the specific mechanism of aspiration in SLN and RLN lesion is different.…”

“…Our own contradictory result around swallow duration likely resulted from using some different individuals in the analysis. Such variation was consistently found in all of the RLN lesion studies (14,19,23) as well as other studies of sensory disruption (25). Thus, in these animals, variation in response to insult seems to characterize dysphagia.…”

“…Before RLN lesion, bolus size, and the success or failure of airway protection were unrelated. After lesion, however, smaller bolus size was associated with safer swallows (19).…”

“…Although insult to either SLN or RLN results in increased aspiration (16,17), these two lesions impact the size and shape of the bolus in infant animal models differently (13,18,19). After surgical transection of the right SLN, the volume of the bolus was greater (13), although bolus size was not associated with increased aspiration.…”

Recurrent laryngeal nerve transection in mice results in translational upper airway dysfunction

“…An infant pig model of RLN injury has provided novel insights concerning the role of the RLN and its neural connections in swallowing behavior. By using videofluoroscopic techniques, RLN injury has been shown to result in compromised airway protection and esophageal dysphagia (Gould et al, 2015), alterations in tongue shape (Gould, Yglesias, Ohlemacher, & German, 2017), and modified tongue and epiglottis kinematics during swallowing (Gould et al, 2016). However, these experiments were performed in neonatal and pre-weanling animals, better representing infants with immature nervous systems.…”