Visco-elastic changes of vocal fold mucosa related to high and low relative air humidity

Abstract

Objective. To study the effects of high and low relative air humidity (RH) on the visco-elastic properties of the vocal fold cover. Materials and methods. The vocal fold mucosa of sheep larynges was microdissected. The mucosal specimens were attached on one side to an oscillator and on the other side to a force transducer. A sinusoidal oscillation (stress) was applied to the specimen and the transduced force (strain) was recorded in two different conditions of a continuous passing airflow: either dry air (RH = 0%) or humid air (RH = 100%). Of the recorded stress and strain curves the gain and phase-shift between the curves were computed and from these parameters stiffness and viscosity were calculated. In both air conditions the deep surface of the specimen was in contact with a saline bath. Results. Stiffness and viscosity both increased significantly more in dry air than in humid air. This increased stiffness and viscosity returned to baseline values after rehydration. Conclusion. We conclude that these findings indicate that changes in the RH of the airflow passing over the vocal cords influences the visco-elastic properties of the vocal cord cover.