Study of Phonation in the Excised Canine Larynx

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Abstract
Previous studies have demonstrated that the laryngeal muscles responsible for pitch variation and vocal efficiency are the cricothyroid muscles, affecting longitudinal tension of the vocal folds, and the thyroarytenoid muscles, controlling the lateral stiffness of the vocal folds. Longitudinal tension in the vocal fold is easily simulated in the excised canine larynx. The effect of the thyroarytenoid muscle, however, has not been adequately analyzed. To simulate the effect of the thyroarytenoid muscle, small balloons were placed in the paraglottic space at the level of the vocal folds in 10 excised canine laryngés. These balloons (Fogarty catheters) could be inflated in increments to simulate the effect of the thyroarytenoid muscle contraction in altering the lateral stiffness of the vocal fold. During phonation subglottic pressure, vocal fold longitudinal tension and balloon size were systematically varied. The photoglottographic and electroglottographic signals, sound intensity, and airflow rate were measured. Multiple regression analysis showed that sound intensity was directly related to subglottic pressure (p < 0.001) and inversely related to balloon size (p < 0.001). Vocal efficiency was directly related to subglottic pressure (p < 0.001). Frequency of vibration was directly related to balloon size (p < 0.05), vocal fold tension (p < 0.001), and subglottic pressure (p < 0.001). Open quotient was directly related to vocal fold tension (p < 0.01) and inversely related to balloon size (p < 0.001). Clinical implications of these results will be discussed.