Vocal fold vibration in simulated head voice phonation in excised canine larynges.

In order to establish precise vibratory patterns and their clinical implication for phonation, the mode of vibration of the vocal folds around the time of register transition in excised canine larynges was analyzed multi-directionally according to various acoustic parameters. Phonation was simulated by artificially tensing the cricothyroid muscles. Vibration of the vocal folds around the time of register transition was filmed from above using ultra-high-speed cinematography and in a frontal plane using X-ray stroboscopy. Acoustic parameters included subglottic pressure, pitch, intensity and tension and were recorded simultaneously during register transition. The fundamental vibration patterns observed during vocal phonation were the same as that involved in chest voice phonation in excised canine larynges, with respect to the traveling wave of the vocal fold vibration. Changes in the physical properties of the vocal folds were considered to occur at register transition. These changes were probably strongly dependent upon changes in the structure of the lamina propria. Head voice phonation requires adaptability of the lamina propria and is less efficient than chest voice phonation. Hence, head voice phonation would be one method for assessing the condition of the vocal folds.