Measurement of mucosal wave propagation and vertical phase difference in vocal fold vibration.

Examination of the surface wave properties of the vocal fold mucosa is becoming an important part of assessment of vocal function. A key wave property is propagation velocity, which determines the phase delay between the upper and lower margins of the vocal folds. Excised canine larynges were used to measure this phase delay, and therewith propagation velocity. The motion of two flesh points was tracked stroboscopically. Differential displacements between the flesh points were matched to displacements of a model. A least-squared fit of the data to the model provided the numeric values of propagation velocity, which varied from 0.5 m/s to about 2.0 m/s, depending on fundamental frequency. The corresponding phase delay along the medial surface of the vocal folds varied from about 60 degrees/mm to 30 degrees/mm.