Measurement of vocal fold intraglottal pressure and impact stress.

Intraglottal pressure was measured according to a previously described hemilarynx procedure. Three phases were identified for intraglottal pressure: an impact phase, in which the vocal folds come into contact and produce a sharp pressure pulse; a preopen phase, in which there is a progressive pressure buildup due to increased exposure of the vocal fold surfaces to subglottal pressure; and an open phase, in which intraglottal pressure becomes aerodynamic and drops gradually from opening to closing. Impact pressure peaks were positively related to subglottal pressure, elongation, and adduction of the vocal folds. The midpoint of the membranous vocal fold received the maximum impact stress. The experimental results match well with analytical predictions and support a current theory of mechanical trauma leading to vocal nodules.