Correlating Vocal Fold Bowing and Thyroarytenoid Myocyte Dimensions in an Aging Rat Model

Laryngeal muscle atrophy is hypothesized to contribute to vocal fold changes observed in age-related vocal atrophy (ARVA). Although rat models are used to study laryngeal aging, it is unclear whether rats experience similar age-related changes. The primary aim was to quantify vocal fold atrophy endoscopically in aging rats, with a secondary aim to examine laryngeal histology and correlate muscle fiber morphometry with endoscopic findings.

4-, 18-, and 24-month-old Sprague-Dawley rats were used (n = 24). Endoscopic video of the vocal folds was collected. Bowing Index (BI) was independently measured by two reviewers. Thyroarytenoid muscles were analyzed to calculate myofiber number, minimum Feret diameter (MFD), and cross-sectional area (CSA).

BI was greater in 18- and 24-month rats than in 4-month rats (MD 7.15, 95% CI: 4.39-9.90; and MD 4.26, 95% CI: 1.50-7.01, respectively). Mean MFD was 19.8 ± 1.3 μm at 4 months, 22.1 ± 1.7 μm at 18 months, and 22.5 ± 1.5 μm at 24 months (4 vs. 18, p = 0.014; 4 vs. 24, p = 0.005; 18 vs. 24, p = 0.87). Mean CSA was 435.8 ± 49.4 μm², 535.2 ± 81.3 μm², and 556.6 ± 54.3 μm² at 4, 18, and 24 months, respectively (4 vs. 18, p = 0.013; 4 vs. 24, p = 0.003; 18 vs. 24, p = 0.780).

Aged rats exhibited increased vocal fold bowing, paralleling ARVA clinical findings. Aged rats also demonstrated an increase in myofiber size. Future studies will investigate the mechanisms driving increased myofiber size with vocal fold bowing, including shifts in muscle fiber type, compensatory hypertrophy, and altered mitochondrial function.

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