Modeling the effects of a posterior glottal opening on vocal fold dynamics with implications for vocal hyperfunction.

Despite the frequent observation of a persistent opening in the posterior cartilaginous glottis in normal and pathological phonation, its influence on the self-sustained oscillations of the vocal folds is not well understood. The effects of a posterior gap on the vocal fold tissue dynamics and resulting acoustics were numerically investigated using a specially designed flow solver and a reduced-order model of human phonation. The inclusion of posterior gap areas of 0.03-0.1 cm(2) reduced the energy transfer from the fluid to the vocal folds by more than 42%-80% and the radiated sound pressure level by 6-14 dB, respectively. The model was used to simulate vocal hyperfucntion, i.e., patterns of vocal misuse/abuse associated with many of the most common voice disorders. In this first approximation, vocal hyperfunction was modeled by introducing a compensatory increase in lung air pressure to regain the vocal loudness level that was produced prior to introducing a large glottal gap. This resulted in a significant increase in maximum flow declination rate and amplitude of unsteady flow, thereby mimicking clinical studies. The amplitude of unsteady flow was found to be linearly correlated with collision forces, thus being an indicative measure of vocal hyperfunction.