Human phonation does not merely depend upon the vibration of the vocal folds. The false vocal fold (FVF), as an important laryngeal constriction, has also been found by more and more research both in clinically and computer simulations that it plays an important role during phonation and contributes significantly to the aerodynamics and sound generation processes of human voice production. Among many parameters which are used to determine and describe the geometry of the false vocal folds, the false vocal fold gap (GFVF), which means the minimal distance between the two false vocal folds, is regarded as an important and dominant parameter. Therefore, this study explores the effects of the FVF gaps on the intralaryngeal pressure distributions, laryngeal resistance and flows using both three-dimensional Plexiglas model and commercially available computational fluid dynamics code. Three glottal angles, divergent 40°, uniform 0°, and convergent -40°were used for this study to explore the effects of FVF gaps, as they represent the basic glottal shapes typically expected in phonation, the angle values also were typically expected for most phonation in modal Register. A wide variety of FVF gaps (GFVF) were parameterized with 12 different values: 0.02, 0.04, 0.06, 0.08, 0.09, 0.1, 0.11, 0.12, 0.16, 0.2, 0.4, 0.6 cm to represent important geometries often appearing within phonatory vibratory cycles. These gaps were used for each glottal angle. The specific design of the FVFs followed prior literature. The minimal glottal diameter (Dg) was constantly at 0.06 cm in this study for each FVF gaps, and the translaryngeal pressure were held constant at 8 cm H2O. A nonvibrating laryngeal airway Plexiglas model, which had linear dimensions 1.732 times of a normal male larynx, was used in this study. In order to measure pressures inside the Plexiglas model, twelve cylindrical ducts were made on the midline of the laryngeal wall of the model. The diameter of each duct was 0.07 cm human size (0.12 cm in the model), so that the connector of an Entran EPE-551 pressure transducer could fit snugly into the holes. The distance between the centers of each hole was 0.14 cm human size. FLUENT (Fluent, Inc., Lebanon, NH), a commercially available computational fluid dynamics code was also used to obtain estimates of the normal wall pressures along the laryngeal surfaces (including the surfaces of vocal folds, ventricles, and false vocal folds) as a function of the FVF gaps and the glottal angles.
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