Quantitative evaluation of the effects of thyroarytenoid muscle activity upon pliability of vocal fold mucosa in an in vivo canine model.

Abstract

Stiffness of the vocal fold is a significant factor in determining mucosal wave propagation and in the control of the fundamental frequency of phonation. We measured pliability of the vocal fold mucosa in an in vivo canine model as an index of stiffness while the histological layer-by-layer structure of the vocal fold was not disrupted. The point 1 mm below the free edge showed a maximal pliability that gradually diminished toward the tracheal side and reached a minimum. When the thyroarytenoid (TA) muscle contracted, pliability of the mucosa was significantly increased (P < 0.001). Mucosal pliability of the excised larynx was significantly increased compared with that in vivo (P < 0.001). The point of minimal pliability in the absence of TA muscle contraction did not shift after excision of the larynx, while TA muscle contraction caused a downward shift of the point of minimal pliability. Mucosal pliability can thus be used to quantitatively assess the effects of TA muscle contraction on stiffness of the vocal fold mucosa.