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Purpose: Therapies for certain voice disorders purport principles of skeletal muscle rehabilitation to increase muscle mass, strength, and endurance. However, applicability of limb muscle rehabilitation to the laryngeal muscles has not been tested. In this study, the authors examined the feasibility of the rat thyroarytenoid muscle to remodel as a consequence of increased activity instantiated through chronic electrical stimulation.
Method: Twenty adult Sprague-Dawley rats (Rattus norvegicus), assigned to a 1-week or 2-week stimulation group, were implanted with a nerve cuff electrode placed around the right recurrent laryngeal nerve and were fitted with a head connector. All animals were placed under anesthesia twice a day for 1 hr each time. Following the training, rats were killed, and thyroarytenoid muscles were isolated for histology and immunohistochemistry.
Results: Mean muscle fiber area decreased, neuromuscular junction density increased, mitochondrial content increased qualitatively, and glycogen-positive fibers increased, demonstrating exercise-induced changes similar to those seen in limb muscles after endurance training.
Conclusion: Rat thyroarytenoid muscles are capable of remodeling in response to chronic electrical stimulation.
Key Words: chronic nerve stimulation, thyroarytenoid, mitochondria, neuromuscular junction, fiber size, glycogen
Voice production is the result of a balanced and highly refined interplay among the intrinsic and extrinsic laryngeal muscles, the respiratory tract, and the supraglottal resonators (Stemple, Lee, D'Amico, & Pickup, 1994). Laryngeal pathology, neuromuscular impairment, and learned patterns of muscle misuse are all thought to contribute-to different extents-to disturb this balance and to impair voice production. In fact, voice disorder is a common communication disorder across the life span, with a lifetime prevalence of 29.9% and point prevalence of 6.6% in the working age population (Roy,Merrill, Gray,&Smith, 2005). Studies conducted in treatment-seeking populations suggest that a significant fraction of patients have laryngeal muscle dysfunction (Coyle,Weinrich, & Stemple, 2001; Herrington-Hall, Lee, Stemple, Niemi, & McHone, 1988). Over the years, behavioral voice therapies have been applied in treatmentseeking populations to reduce aberrant patterns of laryngeal muscle behavior and restore normal patterns of intrinsic muscle function (Colton, Casper, & Leonard, 2006; Hicks & Bless, 1988; Stemple, Glaze, & Klaben, 2009; Stemple & Thomas, 2009). Some approaches explicitly represent a physiological perspective (Colton et al., 2006; Stemple et al., 2009). The theoretical basis for vocal rehabilitation is frequently taken from the exercise physiology field and rests...