Influence of supraglottal tract on intraglottal pressure during vocal fold closing in human phonation

Two-dimensional fluid–structure interaction (FSI) simulations were conducted to study the influence of the supraglottal tract on intraglottal pressure during vocal fold closing in human phonation. The FSI framework couples a three-mass vocal fold model, an incompressible Navier–Stokes flow solver, and a linear perturbed compressible acoustic solver. Four configurations were simulated under varying subglottal pressures, combining divergent and nearly straight vocal fold closing patterns with and without a supraglottal tract. Comparison of straight closing configurations with and without a supraglottal tract revealed the isolated effect of supraglottal inertance, while the analysis of divergent closing configurations showed the combined effects of supraglottal inertance and intraglottal flow separation. Parameters, including the glottal opening, glottal angle, medial surface wall pressure, which directly reflects how intraglottal pressure is converted to the driving force of the vocal fold motion, and intraglottal flow dynamics, were analyzed. The results show that the supraglottal tract influences intraglottal pressure, as well as the medial surface wall pressure, through two primary mechanisms. First, it reduces medial surface wall pressure through inertance effects during flow deceleration. Second, in the divergent closing configurations, it further decreases medial surface wall pressure by intensifying the flow separation effect. This enhanced flow separation effect is because the supraglottal tract increases peak jet velocity during glottis closing, which strengthens the shear layer and enhances flow circulation after flow separation. Consequently, it leads to more negative glottal pressure, particularly under high subglottal pressures.