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

Abstract

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 H(2)O. In each case, the glottal wall "on the left" was chosen to have an angle of 0 degrees with the midline, and the angle of the glottal wall "on the right" was varied through converging angles of 5 degrees, 10 degrees, and 20 degrees and diverging angles of 5 degrees, 10 degrees, and 20 degrees. The case of two parallel glottal walls, or the uniform glottis, was also examined. With the exception of the 20 degrees 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 degrees case were as large as 7% or 8%, and for the 20 degrees 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 H(2)O 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 degrees and 20 degrees. Some possible implications of the observed pressures for phonosurgery are discussed.

Validation of a flow–structure-interaction computation model of phonation

“…Secondly, a comparison is made between flow pressures obtained from experiments on rigid VFs resembling instantaneous deformed VF shapes and those obtained from the full FSI computation with vibrating VFs. In previous experimental studies with rigid VF glottal shapes resembling instantaneous deformed VF shapes (Guo and Scherer, 1993; Scherer et al, 2001, 2002; Shinwari et al, 2003; Scherer et al, 2010; Fulcher et al, 2010) flow pressure on the VF walls have been reliably obtained. Such studies were motivated by the quasi-steady approximation (McGowan, 1993), which states that the instantaneous flow field though a vibrating glottis is not significantly altered if the deformation of the glottis is frozen in time.…”

Phonation threshold pressure: Comparison of calculations and measurements taken with physical models of the vocal fold mucosa

“…The higher concentration requires larger values of the product B*c and the constant P 0 , consistent with an interpretation of increased viscous damping. Equation (17) readily reproduces the linear trends of the data that begin near n 0 ¼ 0.05 cm. The deviations of the data from linearity below 0.05 cm are those referred to in the Introduction, and the merits of two possible explanations, collisions of the vibrating membrane with the opposite wall, 7 or viscosity effects based on Poiseuille flow, 10 will be addressed in the next section.…”

“…A new parameterization of the surface wave model, which was consistent with these observations, was introduced in Eqs. (16) and (17). The new parameterization was shown to require the determination of two constants, Bc and P 0 , for each of the experiments reported by Chan and Titze.…”

Viscous effects in a static physical model of the uniform glottis

“…In model M5, the scale factor was increased to 7.5, which allowed the introduction of more pressure taps along the vocal fold surfaces. [11][12][13][14][15][16] A schematic diagram of the medial surfaces of the Plexiglas vocal fold inserts used to define the glottal constriction of M5 13,14,16 is shown in Fig. 1.…”

“…1) for model M5. Long shims and feeler gauges 13,16 were used between the vocal folds and the wind tunnel wall to adjust the glottal diameter (separation between the medial surfaces of Fig. 1), so that pressure distributions could be measured at minimal diameters of d ¼ 0.005, 0.0075, 0.01, 0.02, 0.04, 0.08, 0.16, and 0.32 cm.…”