Videofluoroscopic Validation of a Translational Murine Model of Presbyphagia.

Presbyphagia affects approximately 40% of otherwise healthy people over 60 years of age. Hence, it is a condition of primary aging rather than a consequence of primary disease. This distinction warrants systematic investigations to understand the causal mechanisms of aging versus disease specifically on the structure and function of the swallowing mechanism. Toward this goal, we have been studying healthy aging C57BL/6 mice (also called B6), the most popular laboratory rodent for biomedical research. The goal of this study was to validate this strain as a model of presbyphagia for translational research purposes. We tested two age groups of B6 mice: young (4-7 months; n = 16) and old (18-21 months; n = 11). Mice underwent a freely behaving videofluoroscopic swallow study (VFSS) protocol developed in our lab. VFSS videos (recorded at 30 frames per second) were analyzed frame-by-frame to quantify 15 swallow metrics. Six of the 15 swallow metrics were significantly different between young and old mice. Compared to young mice, old mice had significantly longer pharyngeal and esophageal transit times (p = 0.038 and p = 0.022, respectively), swallowed larger boluses (p = 0.032), and had a significantly higher percentage of ineffective primary esophageal swallows (p = 0.0405). In addition, lick rate was significantly slower for old mice, measured using tongue cycle rate (p = 0.0034) and jaw cycle rate (p = 0.0020). This study provides novel evidence that otherwise healthy aging B6 mice indeed develop age-related changes in swallow function resembling presbyphagia in humans. Specifically, aging B6 mice have a generally slow swallow that spans all stages of swallowing: oral, pharyngeal, and esophageal. The next step is to build upon this foundational work by exploring the responsible mechanisms of presbyphagia in B6 mice.