Pressure Distributions in a Static Physical Model of the Hemilarynx: Measurements and Computations

An experimental study of the pressure distributions in an asymmetric larynx, hereafter referred to as a hemilarynx, was carried out at a glottal diameter of 0.04 cm and transglottal pressures of 3, 5, 10, 20, and 40 cm H2O. In each case, the glottal wall “on the left” was chosen to have an angle of 0° with the midline, and the angle of the glottal wall “on the right” was varied through converging angles of 5°, 10°, and 20° and diverging angles of 5°, 10°, and 20°. The case of two parallel glottal walls, or the uniform glottis, was also examined. With the exception of the 20° convergent case, the pressure distributions for most angles and pressures were bistable; that is, a stable flow situation persisted when the glottal exit flow jet was directed downstream either to the right or to the left in the rectangular “pharynx” tunnel. Bistability also occurred for the uniform glottis. Pressure differences arising from the different directions of the flow jet were often found to be small; however, differences for the diverging 10° case were as large as 7% or 8%, and for the 20° divergent case, 12%. Calculations with FLUENT, a computational package, gave excellent agreement with observed pressures. Implications of the pressure distribution data for the functional similarity of normal and hemilaryngeal phonation, hypothesized by Jiang and Titze, are discussed. In particular, the intraglottal pressures for converging and diverging angles for the hemilarynx were found to be quite similar to those of the full larynx with the same diameter and included angle or twice the diameter and twice the included angle, suggesting that the same mechanism of energy transfer operates in the two cases. Nondimensionalizing the pressure distributions with the transglottal pressures suggests that the shapes of the distributions at P = 3, 5, 10, 20, and 40 cm H2O for a given geometry are similar. The pressure average of these dimensionless distributions may be interpreted as a template at that geometry, a description referred to as successful pressure scaling. When the entire data set is considered, variations from consistent pressure scaling averaged 1.4%, although these variations tend to be somewhat larger near the glottal entrance and for diverging angles of 10° and 20°. Some possible implications of the observed pressures for phonosurgery are discussed.