Human phonation does not always involve symmetric motions of the two vocal folds. Asymmetric motions can create slanted or oblique glottal angles. This study reports intraglottal pressure profiles for a Plexiglas model of the larynx with a glottis having a 10-degree divergence angle and either a symmetric orientation or an oblique angle of 15 degrees. For the oblique glottis, one side was divergent and the other convergent. The vocal fold surfaces had 14 pressure taps. The minimal glottal diameter was held constant at 0.04 cm. Results indicated that for either the symmetric or oblique case, the pressure profiles were different on the two sides of the glottis except for the symmetric geometry for a transglottal pressure of 3 cm H2O. For the symmetric case, flow separation created lower pressures on the side where the flow stayed attached to the wall, and the largest pressure differences between the two sides of the channel were 5%-6% of the transglottal pressure. For the oblique case, pressures were lower on the divergent glottal side near the glottal entry and exit, and the cross-channel pressures at the glottis entrance differed by 27% of the transglottal pressure. The empirical pressure distributions were supported by computational results. The observed aerodynamic asymmetries could be a factor contributing to normal jitter values and differences in vocal fold phasing.

Modeling the human larynx can provide insights into the nature of the flow and pressures within the glottis. In this study, the intraglottal pressures and glottal jet flow were studied for a divergent glottis that was symmetric for one case and oblique for another. A Plexiglas model of the larynx (7.5 times life size) with interchangeable vocal folds was used. Each vocal fold had at least 11 pressure taps. The minimal glottal diameter was held constant at 0.04 cm. The glottis had an included divergent angle of 10 degrees. In one case the glottis was symmetric. In the other case, the glottis had an obliquity of 15 degrees. For each geometry, transglottal pressure drops of 3, 5, 10, and 15 cm H2O were used. Pressure distribution results, suggesting significantly different cross-channel pressures at glottal entry for the oblique case, replicate the data in another study by Scherer et al. [J. Acoust. Soc. Am. 109, 1616-1630 (2001b)]. Flow visualization using a LASER sheet and seeded airflow indicated separated flow inside the glottis. Separation points did not appear to change with flow for the symmetric glottis, but for the oblique glottis moved upstream on the divergent glottal wall as flow rate increased. The outgoing glottal jet was skewed off-axis for both the symmetric and oblique cases. The laser sheet showed asymmetric circulating regions in the downstream region. The length of the laminar core of the glottal jet was less than approximately 0.6 cm, and decreased in length as flow increased. The results suggest that the glottal obliquity studied here creates significantly different driving forces on the two sides of the glottis (especially at the entrance to the glottis), and that the skewed glottal jet characteristics need to be taken into consideration for modeling and aeroacoustic purposes.

A Plexiglas model of the larynx, having a uniform duct shape and minimal diameter of 0.04 cm, was used to obtain wall pressure distributions resulting from internal airflow. Both a symmetric glottis (obliquity of 0 degrees) and a slanted glottis (obliquity of 20 degrees) were used. The oblique glottis (i.e., a glottis that slants relative to the axial tracheal flow) is present in both normal and abnormal phonation. Obliquity has been shown to create unequal cross-channel pressures on the vocal fold surfaces [Scherer et al., J. Acoust. Soc. Am. 109, 1616 (2001)], and the study here continues this line of research. For the oblique glottis, one side was divergent and the other convergent. Transglottal pressures from 3 to 15 cm H2O using constant airflows were used. Results indicated that the pressure distributions on the two sides of the glottis were essentially equal for the symmetric uniform case (pressures differed slightly near the exit due to asymmetric flow downstream of the glottis). For the oblique glottis, the pressures on the vocal fold surfaces at glottal entry differed by 21.4% of the transglottal pressure, suggesting that this oblique glottis creates upstream glottal pressures that may influence out-of-phase motion of the two vocal folds.

Modeling the human larynx can provide insights into the nature of flow within the glottis. This study reports intraglottal pressure profiles and flow visualization for a symmetric and an oblique glottis with a glottal angle of 10 deg divergence. For the oblique case, the glottis slanted at an angle of 15 deg. A Plexiglas model of the larynx was used. Each vocal fold had at least 11 pressure taps. The minimal glottal diameter was held constant at 0.04 cm. Each case was subjected to steady airflow corresponding to transglottal pressure drops of 3, 5, 10, and 15 cm H2O. Pressure profile results showed that pressures were different on the two sides of the glottis; these data were strongly supported by an earlier study using a different model. Flow visualization in all cases showed that flow separated from one side of the glottis and remained attached to the other. For the oblique case, the separation point on the divergent wall moved upstream in the glottis with greater flows. The laminar core of the skewed jets decreased in length with higher flows. The jet caused asymmetric circulating regions downstream of the glottis in the reservoir section. [Work supported by NIH.]

Computer models of phonation often rely on aerodynamic equations for flow through the glottis. Usually the aerodynamic equations have come from empirical work with steady-flow models made from hard material. The equations simplify the pressure-flow-geometry relations through the larynx. The model used here (model M5) has 14 pressure taps on the vocal folds to give rather complete pressure profiles. Pressure profiles will be reported for symmetric glottal shapes, a minimal diameter of 0.04 cm, and nine glottal angles (uniform; convergent, and divergent 5, 10, 20, and 40 deg) for transglottal pressures of 3, 5, 10, and 15 cm H2O. The glottis is rectangular in the anterior–posterior direction, with a glottal length of 1.2 cm. Results indicated that the pressure coefficient for the glottal entrance ranged from 1.09 to 1.60 with an average of 1.33 (compared to van den Berg’s 1.375). The value decreased as flow increased for any specific glottal angle. The transglottal pressure coefficient ranged from 1.00 to 1.82 with an average of 1.28. The average value for the uniform glottis was 1.63. Values decreased as flow increased. Pressure profiles will be compared to predictions from current glottal aerodynamic equations. [Work supported by NIH Grant 1R01DC03577.]