We tested two hypotheses relating to the sensory deficit that follows a unilateral superior laryngeal nerve (SLN) lesion in an infant animal model. We hypothesized that it would result in (1) a higher incidence of aspiration and (2) temporal changes in sucking and swallowing. We ligated the right-side SLN in six 2–3-week-old female pigs. Using videofluoroscopy, we recorded swallows in the same pre- and post-lesion infant pigs. We analyzed the incidence of aspiration and the duration and latency of suck and swallow cycles. After unilateral SLN lesioning, the incidence of silent aspiration during swallowing increased from 0.7 to 41.5 %. The durations of the suck containing the swallow, the suck immediately following the swallow, and the swallow itself were significantly longer in the post-lesion swallows, although the suck prior to the swallow was not different. The interval between the start of the suck containing a swallow and the subsequent epiglottal movement was longer in the post-lesion swallows. The number of sucks between swallows was significantly greater in post-lesion swallows compared to pre-lesion swallows. Unilateral SLN lesion increased the incidence of aspiration and changed the temporal relationships between sucking and swallowing. The longer transit time and the temporal coordinative dysfunction between suck and swallow cycles may contribute to aspiration. These results suggest that swallow dysfunction and silent aspiration are common and potentially overlooked sequelae of unilateral SLN injury. This validated animal model of aspiration has the potential for further dysphagia studies.

A penetration-aspiration scale exists for assessing airway protection in adult videofluoroscopy and fiberoptic endoscopic swallowing studies, however no such scale exists for animal models. The aim of this study was threefold to 1) develop a Penetration-Aspiration Scale (PAS) for infant mammals, 2) test the scale’s intra- and inter-rater reliability, and 3) to validate the use of the scale for distinguishing between abnormal and normal animals. After discussion and reviewing many videos, the result was a 7-Point Infant Mammal PAS. Reliability was tested by having 5 judges score 90 swallows recorded with videofluoroscopy across two time points. In these videos, the frame rate was either 30 or 60 frames per second and the animals were either normal, had a unilateral superior laryngeal nerve (SLN) lesion, or had hard palate local anesthesia. The scale was validated by having one judge score videos of both normal and SLN lesioned pigs and testing the difference using a t-test. Raters had a high intra-rater (average kappa of 0.82, intraclass correlation coefficient (ICC)= 0.92) and high inter-rater reliability (average kappa of 0.68, ICC= 0.66). There was a significant difference in reliability for videos captured at 30 and 60 frames per second for scores of 3 and 7 (p<0.001). The scale was also validated for distinguishing between normal and abnormal pigs (p<0.001). Given the increasing number of animal studies using videofluoroscopy to study dysphagia, this scale provides a valid and reliable measure of airway protection during swallowing in infant pigs that will give these animal models increased translational significance.

Objectives/Hypotheses The Superior Laryngeal Nerve (SLN) is the major sensory nerve for the upper larynx. Damage to this nerve impacts on successful swallowing. The first aim of the study was to assess the effect of unilateral SLN lesion on the threshold volume sufficient to elicit swallowing in an intact pig model; this volume was defined radiographically as the maximum bolus area visible in lateral view. The second aim was to determine if a difference existed between ipsi-lateral and contra-lateral function as a result of unilateral sensory loss, measured as the radiologic density of fluid seen in the valleculae. Finally, we determined if there was a relationship between the threshold volume and the occurrence of aspiration after a unilateral SLN lesion. Study Design Repeated measures animal study. Methods Four female infant pigs underwent unilateral SLN lesion surgery. The maximum vallecular bolus area in lateral view and the relative vallecular density on each side in the dorsoventral view were obtained from videofluoroscopic recordings in both the pre-lesion control and post lesion experimental states. Results In lateral view, the lesioned group had a bigger maximum bolus area than the control group (p<0.001). Although occasional left-right asymmetry in the dorsoventral view was observed,, the vallecular densities were, on average, equal on both the left (intact) and right (lesioned) sides (p>0.05). A bigger maximum bolus area did not predict aspiration in the lesioned group (p>0.05). Conclusion Unilateral SLN lesions increased the swallowing threshold volume symmetrically in right and left valleculae but the increased threshold may not be the main mechanism for the occurrence of aspiration. The Effect of Unilateral SLN Lesion on Swallowing Threshold Volume