Laryngeal reinnervation as treatment for unilateral vocal fold paralysis may result in synkinesis. Synkinesis occurs when a severed recurrent laryngeal nerve (RLN) is repaired; the adductor and abductor fibers, which are intermixed within the common nerve trunk, may grow into the wrong endoneural tubules as the nerve heals. The resulting cross- innervation causes a variable amount of laryngeal incoordination and impaired function. This phenomenon has not previously been studied in detail. In this study, an attempt will be made to characterize the process of laryngeal synkinesis in a canine model, from a physiologic and histochemical perspective. The primary physiologic measure will be laryngeal adductory pressure (LAP), which is obtained by measuring the pressure in a balloon cuff placed between the vocal folds while stimulating the RLN electrically. The LAP plotted against the stimulation frequency gives a frequency response curve with a characteristic slope. Changes in this slope can be used as an indirect physiologic measure of synkinesis. The ability of a nerve to induce a histochemical change in the muscle it is cross-innervating (Buller et al.) can be used to further quantify laryngeal synkinesis. A series of nerve injury and repair experiments which are expected to produce varying degrees of laryngeal synkinesis will be performed. After 6 months of healing, the laryngeal muscles will be harvested and the histochemistry studied (using alkali-stable ATPase staining) to determine how much the muscle has been transformed from fast-to slow-twitch, or vice-versa. This is another indirect measure of laryngeal synkinesis.
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