Objective: To determine the role of the adjustment of expiratory effort in the control of vocal intensity.
Study design: An intensity-loading test was performed by using the airway interruption method. Three groups of subjects were used: a control group thought to resemble normal vocal fold closure, a group of patients with Reinke's edema thought to represent increased mass at the level of the vocal folds, and a group with vocal fold paralysis that was thought to represent a group with lack of adequate vocal fold closure.
Results: In the control group, expiratory lung pressure and airway resistance slightly increased. In the patients with Reinke's edema, expiratory lung pressure, and airway resistance significantly increased. In this group, the voice intensity was controlled by laryngeal adjustment, but a greater expiratory effort was needed because of a greater increase in glottal resistance. In the patients with vocal cord paralysis, airway resistance did not increase even with a high-intensity voice. Vocal intensity was controlled by expiratory effort.
Conclusions: If there is sufficient ability for laryngeal adjustment, vocal intensity is controlled primarily by laryngeal adjustment and by expiratory adjustment in response to increased glottal resistance. However, vocal intensity is controlled by expiratory effort when laryngeal adjustment ability is poor.