Quantification of Vocal Fold Atrophy in an Aging Rat Model

The primary objective of this pilot study was to compare vocal fold morphology between aged and non-aged adult rat vocal folds. Secondarily, we set out to quantify neurophysiologic and histologic differences.

Four-month (non-aged) and 21-month (aged) adult Fischer 344xBrown Norway (F344xBN) hybrid rats were used. Vocal fold measurements including bowing index (BI), abduction angle, and normalized vocal fold width (NVFW) were quantified. Laryngeal evoked response studies were performed by stimulating the recurrent laryngeal nerve (RLN) and recording from the thyro-arytenoid (TA) muscle. Histology was performed on laryngeal muscles and the RLN.

Ten non-aged (4-month) vs. 10 aged (21-month) rat hemi-laryngeal preparations were included. The mean BI was higher in the aged group compared to the non-aged group, 5.02 ± 1.05 vs. 4.12 ± 1.05 units, respectively, and this difference approached statistical significance (difference 0.89 units, 95% CI: -0.10-1.80 units, p = 0.07). CMAP latency was significantly higher in the aged vs. non-aged group, 0.90 ± 0.05 ms compared to 0.84 ± 0.06 ms, respectively (difference 0.06 ms, 95% CI: 0.01-0.11 ms, p = 0.02). Mean % myelin between the non-aged and aged rats was 72.12% ± 8.55% and 65.41% ± 5.38%, respectively, mean difference -6.71% (95% CI: -13.72%-0.31%, p = 0.060). Mean cross-sectional area (CSA) of TA myofibers was significantly increased in the aged rats 81.6 μm² (95% CI: 6.9-156.3 μm², p = 0.034).

Laryngeal evoked responses showed a significant increase in the CMAP latency in aged rats compared to non-aged rats. There was an increase in BI and a decrease in myelination in the aged rat that approached statistical significance. Future adequately powered studies are needed to quantify the difference in endoscopic measures, neurophysiology, and histology.

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