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Aged vocal folds have been reported to have dense collagen deposition and decreased hyaluronic acid (HA) in the lamina propria. These characteristics are thought to contribute to vocal problems that occur with age (presbyphonia). To restore better viscoelasticity to aged vocal folds, an intervention that might increase HA and decrease collagen production from aged vocal fold fibroblasts would appear to be a potentially useful approach. Our previous in vitro study has revealed that basic fibroblast growth factor (bFGF) consistently stimulates HA production and decreases collagen production from aged rat vocal fold fibroblasts. The present in vivo study examined the effects of intracordal injection of bFGF into aged rats' vocal folds in terms of restoration of HA and collagen distribution in the lamina propria. We injected bFGF transorally into the lamina propria of (unilateral) vocal folds. The injection was repeated 4 times weekly, and rats were painlessly sacrificed 1 week, 1 month, and 2 months after the final injection. Histologic examination revealed that bFGF significantly increased the HA content of the lamina propria up to 2 months, but showed no effect on collagen, even after 2 months. Because it might take longer for excessive collagen to be degraded, further studies are necessary to clarify the long-term effect on collagen. A drug delivery system for bFGF also needs to be developed to maximize its effect in the future. The present study suggested at least a positive effect of bFGF in restoring the HA content in the aged vocal fold lamina propria.

Objectives/hypothesis: It has been reported that in aged vocal folds, dense collagen deposition takes place and hyaluronic acid decreases in the lamina propria, which are thought to contribute to the vocal problems occurring with age (presbyphonia). To restore aged vocal folds to their younger state, it seems crucial to address these age-related lamina propria changes. Intervention that might increase hyaluronic acid and decrease collagen would appear to be a potentially useful approach. The present study examined the effects of growth factors on aged fibroblasts in terms of the production of hyaluronic acid and collagen type I., Study Design: In vitro study using animal model., Methods: Fibroblasts were harvested from young and aged rat vocal folds and cultured with or without hepatocyte growth factor and/or basic fibroblast growth factor at different concentrations. Subsequently, the production of hyaluronic acid and collagen type I was examined in the supernatant culture media using enzyme-linked immunosorbent assay., Results: Aged fibroblasts produced less hyaluronic acid than younger fibroblasts. When aged and young fibroblasts were cultured with basic fibroblast growth factor, hyaluronic acid production increased and collagen type I production decreased regardless of the concentration, whereas the effects of hepatocyte growth factor appeared to vary with concentration. The basic fibroblast growth factor also was associated with stimulation of growth of aged fibroblasts., Conclusion: The present results suggest that growth factors, especially basic fibroblast growth factor, may have therapeutic potential in restoration of aged vocal fold.

Deficits in voice and swallowing are found in the elderly, but the underlying neuromuscular mechanisms are unclear. A potential mechanism may be denervation-induced muscle fiber transformation to a slower-contracting type of muscle fiber. This study examined young, old, and denervated rat laryngeal muscles (lateral thyroarytenoid, lateral cricoarytenoid, and posterior cricoarytenoid) to examine differences in myosin heavy chain (MHC) composition. Results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses indicated that all muscles were composed predominately of type IIB MHC. With aging and denervation, type IIB was reduced and type IIX, a slower-contracting isoform, was increased in the lateral thyroarytenoid and lateral cricoarytenoid muscles. In the posterior cricoarytenoid muscle, the MHC composition was relatively unchanged. These findings suggest that aging may affect laryngeal adductory function by altering muscle fiber type composition to a slower-contracting isoform, in a manner similar to that observed with denervation.

Fatigue and weakness in the elderly are the functional consequences of underlying neuromuscular decline. However, little is known about the manifestations of aging in the larynx. This study evaluated the manner in which laryngeal senescence affects laryngeal-respiratory kinematics by videorecording laryngeal motion in both young and old rats. Recorded images were digitized, and glottal displacement and movement rate were measured. The results indicated that the amplitude of change in glottal angle was significantly diminished, and laryngeal movement durations were prolonged in the old animals. These findings may be due to functional constraints on the respiratory system, impaired laryngeal-respiratory interactions, or decrements in vocal fold tension with age. Because of the serious and pervasive nature of dysphagia and communicative impairments in the elderly, research that specifically examines the manifestations and causes of these impairments is of great importance.