Increased Stability of Airflow Following Botulinum Toxin Injection

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Abstract
The purpose of this study was to determine whether stability of airflow, as well as mean airflow, increased following botulinum toxin injection to laryngeal and extralaryngeal muscles in persons with spasmodic dysphonia (SD), some with associated vocal tremor (VT). Aerodynamic data were collected from five subjects before and at 2, 4, and 8 weeks after they received treatment by each of two different arms in an injection protocol in a crossover study. One arm of the protocol involved treatment of the thyroarytenoid muscles only. The other arm involved treatment of both the thyroarytenoid muscles and the strap muscles. Measures of mean airflow and coefficient of variation (COV) of airflow during phonation were obtained. A decrease in the COV of airflow would indicate increased stability of phonatory airflow. Before treatment, all subjects with SD/VT exhibited mean airflows that were similar to controls. The COV of airflow ranged from normal to substantially elevated. Following botulinum injection, mean airflow characteristically increased and COV of airflow decreased. This finding suggests there is a change in the type, as well as the level, of activity in the muscles of speech production following botulinum toxin injection. The increase in airflow stability identified could be due to increased stability of the laryngeal system and possibly of the respiratory system as well.