Physiological Mechanisms of Phonation: Tension of the Vocal Fold Muscle

Abstract

A method was devised to determine, in situ, in the dog, the mechanism by which tension is developed in the thyroarytenoid muscle (vocal fold). The origin of the muscle was dissected from the thyroid cartilage and tied to a force transducer; the arytenoid cartilage was fixed. The recurrent laryngeal nerve was electrically stimulated with square wave pulses. Development of isometric tension was measured as a function of in situ resting length (L_o) and of the strength and frequency of the stimulus. In addition, a passive tension length curve was constructed from L_o to 1.3 L_o. Tension increased sigmoidally with changes in initial muscle length, stimulus voltage, and frequency, reaching a maximum at 1.3 L_o and 120 pulses/sec. Vocal fold tension, a factor in determining fundamental frequency of phonation, was found to be a complex function of the above variables. Clinical implications of findings were discussed.