The Effect of Vocal Fold Inferior Surface Hypertrophy on Voice Function in Excised Canine Larynges

Abstract

This study aimed to explore the changes in vocal fold inferior surface hypertrophy (VFISH) on vocal fold vibration by aerodynamic and acoustic analysis. The present study allows us to gain new insights into the subglottal convergence angle (SCA), which will change with VFISH. The study is prospective, and designed for repeated measures with each excised canine larynx serving as own control. Three degrees of VFISH, initial, mild, and severe, were simulated by injecting different doses of fructose injections into the inferior surface of the vocal folds of 10 excised canine larynges. Computed tomographic images of the larynx were gathered, and three-dimensional models of the airway and vocal folds were reconstructed using the Mimics software. The SCA was measured from the reconstructed models. Phonation threshold flow (PTF), phonation threshold pressure (PTP), and mean flow rate (MFR) were recorded directly in the excised canine larynx phonation setup. Glottal resistance (GR), sound pressure level (SPL), fundamental frequency (F0), and formants 1-4 (F1-4) were measured when subglottal pressure (Psub) was at 1.5 kPa or 2.5 kPa, separately. Using ordinary one-way analysis of variance, we compared the aerodynamic outcomes and voice quality among the three groups of hypertrophy. The SCA, PTP, and PTF increased with the degree of VFISH. When the Psub was controlled at 1.5 kPa or 2.5 kPa, F0 also increased significantly with the degree of VFISH of the excised canine larynges. The MFR, GR, SPL, and F1-4 had little change between the three groups and were not significantly different. The VFISH makes onset phonation more difficult, increases the SCA, and increases the F0 in sustained phonation.