The Physiologic Impact of Unilateral Recurrent Laryngeal Nerve (RLN) Lesion on Infant Oropharyngeal and Esophageal Performance

Abstract

Recurrent laryngeal nerve (RLN) injury in neonates, a complication of patent ductus arteriosus corrective surgery, leads to aspiration and swallowing complications. Severity of symptoms and prognosis for recovery are variable. We transected the RLN unilaterally in an infant mammalian animal model to characterize the degree and variability of dysphagia in a controlled experimental setting. We tested the hypotheses that (1) both airway protection and esophageal function would be compromised by lesion, (2) given our design, variability between multiple post-lesion trials would be minimal, and (3) variability among individuals would be minimal. Individuals' swallowing performance was assessed pre- and post-lesion using high speed VFSS. Aspiration was assessed using the Infant Mammalian Penetration-Aspiration Scale (IMPAS). Esophageal function was assessed using two measures devised for this study. Our results indicate that RLN lesion leads to increased frequency of aspiration, and increased esophageal dysfunction, with significant variation in these basic patterns at all levels. On average, aspiration worsened with time post-lesion. Within a single feeding sequence, the distribution of unsafe swallows varied. Individuals changed post-lesion either by increasing average IMPAS score, or by increasing variation in IMPAS score. Unilateral RLN transection resulted in dysphagia with both compromised airway protection and esophageal function. Despite consistent, experimentally controlled injury, significant variation in response to lesion remained. Aspiration following RLN lesion was due to more than unilateral vocal fold paralysis. We suggest that neurological variation underlies this pattern.

Keywords: Aspiration; Deglutition; Deglutition disorders; Esophagus; Infant; Recurrent laryngeal nerve.

Figure 1

esophageal clearance failure. In a normal swallow, all fluid is cleared from the upper esophagus (A). In a failure event (B), part of the bolus remains in the upper esophagus.

Figure 2

Proximal escape. In a normal swallow, there is no milk proximal to the upper esophageal sphincter (UES) after a swallow (A). In proximal escape (B), fluid returns back through the UES after a swallow.

Figure 3

Examples of distribution of IMPAS scores within sequences pre- (A and B) and post- (C and D) lesion to illustrate variation in occurrence of different scores.

Figure 4

increase in percentage of aspiration events in a sequence through time. C: control; L3h: 3h post- lesion; L24h: 24h post- lesion; L48h: 48h post-lesion.

Figure 5

Change in percentage of penetration events in a sequence over time. C: control; L3h: 3h post- lesion; L24h: 24h post- lesion; L48h: 48h post- lesion.

Figure 6

Average IMPAS score against coefficient of variation for individual feeding sequences in each pig at different time points pre- and post- lesion. It is impossible to have both average and variation high, as, on a scale with an upper bound such as IMPAS, a high average implies little variation in the scores.

Figure 7

a, b, c: examples of different patterns of change in average IMPAS and coefficient of variation over time post- lesion