[Influence of transglottal pressure on vocal fundamental frequency changes with stiffness of vocal folds].

We have described the influence (dF/dP) of transglottal pressure on vocal fundamental frequency (F0). It was previously reported that dF/dP varied with the stiffness of the vocal folds, and that the vocal fold membrane when dry was stiffer than when wet. Normal subjects were injected with atropine sulfate in order to dry their larynx, as a model of stiffer-than-normal vocal folds. Transglottal pressure changes during sustained phonation were applied by partially closing a shutter valve mounted on a mouthpiece. Both before and after atropine sulfate injection, the values of dF/dP, in modal register, decreased and increased as F0 increased, and the smallest values of dF/dP were negative in all subjects. The absolute values of both the largest and smallest dF/dP in subjects with atropine sulfate were smaller than those in normal subjects. These finding indicated that dF/dP is correlated with the stiffness of the vocal folds.