The effect of unilateral superior laryngeal nerve lesion on swallowing threshold volume

Objectives/Hypothesis The superior laryngeal nerve (SLN) is the major sensory nerve for the upper larynx. Damage to this nerve impacts 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 ipsilateral and contralateral function as a result of unilateral sensory loss, measured as the radiologic density of fluid seen in the valleculae. Finally, we determined whether 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 prelesion control and postlesion experimental states. Results In lateral view, the lesioned group had a larger maximum bolus area than the control group (P<.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>.05). A bigger maximum bolus area did not predict aspiration in the lesioned group (P>.05). Conclusions 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.