Laryngeal biomechanics: an overview of mucosal wave mechanics

The biomechanics of wave propagation in viscoelastic materials can be useful in understanding the nature of normal and pathologic vocal fold vibration. Mucosal wave movement is the primary means by which the larynx transforms the egressive pulmonary air flow into sound. This short tutorial describes a number of concepts fundamental to the understanding of the vocal fold traveling wave. The displacement velocity of the vocal folds is shown to be proportional to the wave speed, which in turn is proportional to the elastic modulus or stiffness of the vocal folds. Finally, a few cases of unilateral paralysis are used to demonstrate how vocal fold stiffness, entrainment, and degree of vocal fold closure interact to create the complex vibratory patterns that occur in disordered laryngeal states. It is emphasized that surgical voice restoration must consider these properties of the mucosal wave to improve phonatory function.