The effects of the false vocal fold gaps on intralaryngeal pressure distributions and their effects on phonation

Human phonation does not merely depend on the vibration of the vocal folds. Research by clinical and computer simulations has demonstrated that the false vocal fold (FVF) is an important laryngeal constriction that plays a vital role during human voice production. This study explored the effects of the FVF gaps using both the three-dimensional Plexiglas model and the numerical computation methods. Twelve FVF gaps (ranging from 0.02 to 2.06 cm) were used in this study at three glottal angles (uniform and convergent/divergent 40 degrees ), two minimal glottal diameters (D (g)) (0.04 cm and 0.06 cm) separately, and the constant subglottal pressure (8 cm H(2)O). The results suggested that (1) the intralaryngeal pressure was the lowest and the flow was the highest (least flow resistance) when the FVF gap was 1.5-2 times greater than D (g); (2) the divergent glottal angle gave lower pressure and greater flow than the convergent and uniform glottal angle as there were no FVF conditions; (3) the presence of the FVF decreased the effects of the glottal angle to a certain extent; and more importantly, (4) the presence of the FVF also moved the separation points downstream, straightened the glottal jet for a longer distance, decreased the overall laryngeal resistance, and reduced the energy dissipation, suggesting the significance of FVF in efficient voice production. These results may be incorporated in the phonatory models (physical or computational) for better understanding of vocal mechanics. The results might also be helpful in exploring the surgical and rehabilitative intervention of related voice problems.