Simple and objective methods were developed to evaluate the mechanical properties of the vocal fold in relation to mobility of the vocal fold mucosa and stiffness of the vocal fold. Mobility of the vocal fold mucosa was measured with a fine suction tube, and stiffness of the vocal fold was evaluated by analyzing stress-strain curves in human and canine excised larynges under various conditions.
1) Mobility of the vocal fold mucosa was greatest in the middle of the membranous portion and less around the anterior commissure and the vocal process. Stiffness of the membranous portion of the vocal fold was least at the middle and greater around the anterior commissure and the vocal process. Mobility of the false vocal fold mucosa was much greater, and stiffness of the false vocal fold was much less, than those of the true vocal fold.
2) As the vocal fold tension increased, mobility of the vocal fold mucosa decreased and stiffness of the vocal fold increased as the vocal pitch rose. Marked differences of the mechanical properties were observed between the “body” and the “cover” of the vocal fold, especially when tension was applied to the vocal fold.
3) When the vocalis muscle contracted, the vocal fold tended to be less stiff and more viscous.
4) When the vocal fold mucosa became dry, stiffness of the vocal fold became greater.
5) Submucosal injection of saline solution reduced mobility of the vocal fold mucosa and increased stiffness and viscosity of the vocal fold.
