Effects of Aging on Superior Laryngeal Sensory and Motor Function in a Rat Model.

Abstract

OBJECTIVE: Aging is a risk factor for diminished laryngeal sensation, dysphagia, and aspiration events; however, the mechanisms underlying age-related swallow dysfunction are not well understood. Some of these changes are thought to be mediated through superior laryngeal nerve (SLN) dysfunction. The purpose of this study was to measure the effects of aging on SLN motor and sensory function in a rat model. STUDY DESIGN: Animal study. SETTING: Tertiary-care center. METHODS: Evoked response studies were performed by SLN stimulation. Outcome measures included compound motor (CMAP) and sensory nerve action potential (SNAP) measurements recorded from the cricothyroid muscle and the internal branch of the SLN, respectively. Swallow force measurements were recorded by stimulating the SLN and quantifying the hyoid elevation force. Additionally, force and frequency of electrically and tactile-stimulated swallow reflex were analyzed. These measures were collected in adult Sprague-Dawley rats aged 4, 18, and 24 months. RESULTS: Compared to non-aged rats, advanced age was associated with significantly longer SNAP latency and total duration with a mean difference (95% CI) of 1.23 milliseconds (1.06-1.40) and 2.24 milliseconds (1.89-2.59), respectively. CMAP latency and total duration were also increased by 0.27 milliseconds (0.23-0.31) and 1.5 milliseconds (1.14-1.87), respectively. Advanced age was associated with decreased electrical and tactile-stimulated swallow frequency with a mean difference of 3.3 swallows/10 seconds (95% CI 1.1-5.5) and 2.1 swallows/10 seconds (95% CI 0.71-3.5), respectively. CONCLUSION: Advanced age was associated with longer SNAP and CMAP duration and decreased swallow frequency. The results suggest delayed nerve conduction as a potential mechanism for age-related swallow dysfunction in our rat model. Our work has implications in humans with the hopes for developing targeted therapies for age-related swallow dysfunction. LEVEL OF EVIDENCE: N/A.