Kenneth: The effects of the false vocal folds on translaryngeal airflow resistance

The human larynx is a tube with two orifices, with the false vocal folds (FVF) just above the true vocal folds. The gap between the two false vocal folds can vary during speech and may affect the aerodynamics and aeroacoustics of phonation, the extent of which is not yet known. The present research was conducted to understand the effects of the false vocal fold gap on translaryngeal airflow resistance (translaryngeal pressure divided by volume flow). A scaled-up static Plexiglas model of an adult larynx was used. Prior to simulating the laryngeal geometry, a study was conducted to determine the shape and size of the false vocal fold region using human laminagrams obtained during phonation. Selected features from the results of the study were used to build models of the false vocal folds. These were placed in the Plexiglas model of the larynx to study the effects of the false vocal fold gap on translaryngeal airflow resistance. The FVF gap was parametrically varied for each of five glottal diameters and five glottal angles. Seven different pressure drops were used for each laryngeal geometry. Results showed that the translaryngeal airflow resistance decreased by about 10-25 % for all glottal diameters for specific FVF gap sizes. Minimum airflow resistance for any glottal condition was observed when the false vocal fold gap was about twice the minimal glottal diameter. The airflow resistance was lowered more for converging and uniform cases than for divergent ones. For glottal diameters of 0.04 and 0.08 cm, the airflow resistance was lowered for a wider range of FVF gaps than for glottal diameters of 0.16 and 0.32 cm. A best fit for the entire data is also provided. This decrease in translaryngeal airflow resistance may be indicative of efficient voice production, and may suggest target laryngeal anatomy for optimal surgical and rehabilitative vocal intervention. 1