Glottal Angle Research Articles

Intraglottal pressures in a three-dimensional model with a non-rectangular glottal shape

This study used a symmetric, three-dimensional, physical model of the larynx called M6 in which the transverse plane of the glottis is formed by sinusoidal arcs for each medial vocal fold surface, creating a maximum glottal width of 0.16 cm at the location of the minimal glottal area. Three glottal angles were studied: convergent 10 degrees, uniform (0 degrees), and divergent 10 degrees. Fourteen pressure taps were incorporated in the upstream-downstream direction on the vocal fold surface at three coronal locations, at the one-fourth, one-half, and three-fourths distances in the anterior-posterior direction of the glottis. The computational software FLUENT was used to compare and augment the data for these cases. Near the glottal entrance, the pressures were similar across the three locations for the uniform case; however, for the convergent case the middle pressure distribution was lower by 4% of the transglottal pressure, and lower by about 2% for the divergent case. Also, there were significant secondary velocities toward the center from both the anterior commissure and vocal process regions (of as much as approximately 10% of the axial velocities). Thus, the three dimensionality created relatively small pressure gradients and significant secondary velocities anteriorly-posteriorly within the glottis.

The effects of the false vocal fold gaps on intralaryngeal pressure distributions and their effects on phonation

Human phonation does not merely depend on the vibration of the vocal folds. Research by clinical and computer simulations has demonstrated that the false vocal fold (FVF) is an important laryngeal constriction that plays a vital role during human voice production. This study explored the effects of the FVF gaps using both the three-dimensional Plexiglas model and the numerical computation methods. Twelve FVF gaps (ranging from 0.02 to 2.06 cm) were used in this study at three glottal angles (uniform and convergent/divergent 40 degrees ), two minimal glottal diameters (D (g)) (0.04 cm and 0.06 cm) separately, and the constant subglottal pressure (8 cm H(2)O). The results suggested that (1) the intralaryngeal pressure was the lowest and the flow was the highest (least flow resistance) when the FVF gap was 1.5-2 times greater than D (g); (2) the divergent glottal angle gave lower pressure and greater flow than the convergent and uniform glottal angle as there were no FVF conditions; (3) the presence of the FVF decreased the effects of the glottal angle to a certain extent; and more importantly, (4) the presence of the FVF also moved the separation points downstream, straightened the glottal jet for a longer distance, decreased the overall laryngeal resistance, and reduced the energy dissipation, suggesting the significance of FVF in efficient voice production. These results may be incorporated in the phonatory models (physical or computational) for better understanding of vocal mechanics. The results might also be helpful in exploring the surgical and rehabilitative intervention of related voice problems.

Intraglottal pressure distributions for oblique glottal angles

Asymmetric vocal fold oscillation occurs for both normal and pathological phonation. The pressures on the right and left glottal walls receive different pressures when the glottis is oblique, as we have shown previously. Different driving forces may affect the motion, although to what extent is not yet known. We have continued empirical modeling of various oblique glottal shapes using a Plexiglas model (M5), and report the findings of those studies. In general, an oblique glottis tends to receive higher pressures on the more convergent side, and the cross-channel pressure differences may shift polarity between upstream and downstream sections. The effects on intraglottal pressures for a wide range of obliquity, minimal glottal diameter, transglottal pressure, and included glottal angle will be shown and discussed relative to potential oscillatory effects. [supported by NIH R01DC03577]

Dynamic MRI of Larynx and Vocal Fold Vibrations in Normal Phonation

Dynamic magnetic resonance imaging (MRI) of the larynx and vocal folds during phonation was used for measuring the vertical laryngeal movements and the glottal angle of the vocal folds opening and closing in dynamic phase. The data used in this analysis were taken on 10 healthy volunteers during maximal inspiration and the prolonged phonation of the vowels [i] (as in key), [a] (as in car), [u] (as in loop), and the consonant [sh] (as in ship). The results of our MRI data have demonstrated the difference of the vocal folds movement in relation to the vowel and consonant sounds, with a large glottal opening for [sh] and a narrow opening for [i] and [u], and the difference of the laryngeal position in relation to the vowels, with [a] and [u] having a lower larynx position than [i]. Imaging the larynx's positions and the vocal folds' vibrations is possible using dynamic MRI. This technique permits measurements of laryngeal structures and glottal parameters in dynamic function with multiplanar high-resolution imaging. Analysis of laryngeal activity and vocal folds' vibration may be helpful for the evaluation of the phonation function and for the understanding of the physiology of vocal production and voice modulation.

Intraglottal pressures relative to laryngeal airway configuration

This presentation summarizes results of empirical and computational studies with steady flow to indicate how normal intraglottal pressures vary as a function of (a) glottal angle, (b) radius of the glottal entrance and exit, (c) glottal obliquity, (d) inferior and superior vocal fold surface angles, and (e) false vocal fold gap. Empirically obtained intraglottal pressures differ in significant ways from earlier theoretical work and current simplified expressions. Intraglottal pressures are highly sensitive to glottal angle, entrance radius for the diverging glottis, and the exit radius for the converging glottis. Air pressures in the glottis are asymmetric when the flow is asymmetric, as they typically are in the divergent glottis. The oblique glottis produces asymmetric pressures that depend upon vocal fold angle and flow separation. Intraglottal pressures are typically lower on the side where velocities are faster. Intraglottal pressures are essentially independent of the wide range of inferior and superior vocal fold surface angles found in the human. When the ratio of the false fold gap to glottis minimal diameter is about 2, laryngeal flow resistance and intraglottal pressures reduce; flow resistance and intraglottal pressures quickly increase for gap ratios less than one. [Work supported by NIH R01DC03577.]

The effects of the false vocal folds on laryngeal pressures and flows

As a laryngeal constriction, the false vocal fold (FVF) gap (the distance between the medial edges of the FVFs) may create important effects on phonation by altering the pressures within and flows through the larynx. The computational code FLUENT was used to examine the effects on pressures and flows for FVF gaps ranging from 0.02 to 2.06 cm, for three glottal angles (uniform and convergent/divergent 40 deg) and two minimal glottal diameters (0.04 and 0.06 cm), for constant subglottal pressure (8 cm H2O). The specific design of the FVFs followed prior literature. Results suggest three important ranges of FVF gaps: (1) when the FVF gap was 1.5–2 times the minimal glottal diameter, pressures were lower throughout the larynx, and flows were higher through the larynx (less flow resistance); (2) for smaller FVF gaps, intralaryngeal pressures increased and flows decreased; (3) for greater FVF gaps, pressures and flows were unaffected. Also, (4) the divergent glottal angle gave the greatest flows, (5) flow separation locations for the divergent glottis moved downstream as the FVF gap decreased, and (6) the FVFs straightened the flow for narrow gaps. Thus, the status of the FVFs needs to be considered for voice production and synthesis.

Numerical study of the effects of inferior and superior vocal fold surface angles on vocal fold pressure distributions

Vocal fold geometry plays an important role in human phonation. A wide range of inferior and superior vocal fold surface angles has been shown to be present during phonation [Nanayakkara, Master's thesis, Bowling Green State University, Bowling Green, OH (2005)]. This study explored how these angles affect pressure distributions on the vocal folds, and thus how they may affect phonation. The computational code FLUENT was used to obtain pressure distributions for laminar, incompressible flow. Eighteen inferior vocal fold surface angles and nineteen superior vocal fold surface angles were selected for three specific glottal angles, uniform 0 degrees, convergent 10 degrees, and divergent 10 degrees. Minimal glottal diameter (0.01 cm), transglottal pressure (8 cm H2O), and glottal entrance radius (0.15 cm) were held constant, and the glottal exit radius was constant for each glottal angle. Results suggest that the vocal fold surface pressures are independent of the inferior and superior vocal fold surface angles realistic for human phonation. These results suggest that, in contrast to the important effects of glottal entrance and exit radii, minimal diameter, and angle on intraglottal pressures, the inferior and superior vocal fold surface angles (excluding possible interactive effects with the false vocal folds) do not have an influence on the intraglottal pressures.

An experimental analysis of the pressures and flows within a driven mechanical model of phonation

The production of voice is related to the flow of air through the glottis, whose time-dependent shape is defined by the motion of the vocal folds and the translaryngeal pressure. A scaled dynamically similar experimental apparatus that mimics the motion of the vocal folds was designed and built, such that both the glottal diameter and glottal angle change during a motion cycle. This motion is more realistic than in other reported dynamic models. The motion of the folds can be driven at different frequencies. The glottal flow takes place at a constant inlet pressure, mimicking the lung pressure. The transglottal pressure difference and flow rate were measured over the motion cycle. Satisfactory agreement was obtained for identical cases by numerically solving the two-dimensional, incompressible Navier-Stokes equations. Both experimental and numerical data showed that the glottal flow rate and transglottal pressure were affected by the oscillation frequency of the vocal folds. Flow visualization showed that the glottal flow patterns, which are a potential source of aero-acoustic sound, are influenced by the oscillation frequency. However, glottal flow resistance depended to a lesser extent on vocal fold oscillation frequency for the portion of the cycle when the glottis was divergent.

Analytic Representation of Volume Flow as a Function of Geometry and Pressure in a Static Physical Model of the Glottis

A static physical model of the larynx (model M5) was used to obtain a large set of volume flows as a function of symmetric glottal geometry and transglottal pressure. The measurements cover ranges of these variables relevant to human phonation. A generalized equation was created to accurately estimate the glottal volume flow given specific glottal geometries and transglottal pressures. Both the data and the generalized formula give insights into the flow behavior for different glottal geometries, especially the contrast between convergent and divergent glottal angles at different glottal diameters. The generalized equation produced a fit to the entire M5 dataset (267 points) with an average accuracy of 3.4%. The accuracy was about seven times better than that of the Ishizaka-Flanagan approach to glottal flow and about four times better than that of a pressure coefficient approach. Thus, for synthesis purposes, the generalized equation presented here should provide more realistic glottal flows (based on steady flow conditions) as suitable inputs to the vocal tract, for given values of transglottal pressure and glottal geometry. Applications of the generalized formula to pulses generated by vocal fold motions typical of those produced by the Ishizaka-Flanagan coupled-oscillator model and the more recent body-cover model of Story and Titze are also included.

The effect of three-dimensional glottal geometry on intraglottal quasi-steady flow distributions and their relationship with phonation

Vocal fold geometry plays an important role in human phonation. The intraglottal quasi-steady pressure and velocity distributions depend upon the shape, size, and diameter of the glottis. This study reports the effects of the variation of glottal shapes on intraglottal pressures and velocities using a Plexiglas model with a glottis having nine symmetric glottal angles (uniform, as well as convergent and divergent 5 degrees, 10 degrees, 20 degrees and 40 degrees), while the minimal glottal diameter was held constant at 0.06 cm. The empirical data were supported by penalty finite element computational results. The results suggest that larger convergent glottal angles correspond to increased pressures and decreased velocities in the glottis upstream of the minimum glottal location, with a reversal of this pattern at the minimal glottal diameter location. The pressure dip near the glottal entrance for divergent glottal angles was greatest for the 10 degrees divergence angle condition, and was sequentially less for 5 degrees, 20 degrees, and 40 degrees. Flow resistance was greater for a convergent angle than a divergent angle of the same value, and least for the 10 degrees divergent condition. Pressure recovery in the glottis suggested that the optimal glottal diffuser angle was near 10 degrees. Results suggest that the glottal geometry has a critical relationship with phonation (especially for vocal efficiency), and therefore important significance to understanding artistic voice and clinical voice management.

The effect of glottal angle on intraglottal pressure

Intraglottal pressure distributions depend upon glottal shape, size, and diameter. This study reports the effects of varying glottal angle on intraglottal and transglottal pressures using a three-dimensional Plexiglas model with a glottis having nine symmetric glottal angles and a constant minimal glottal diameter of 0.06 cm. The empirical data were supported by computational results using FLUENT. The results suggested that (1) the greater the convergent glottal angle, the greater outward driving forces (higher intraglottal pressures) on the vocal folds; (2) flow resistance was greatest for the uniform glottis, and least for the 10 degrees divergent glottis; (3) the greatest negative pressure in the glottis and therefore the greatest pressure recovery for diverging glottal shapes occurred for an angle of 10 degrees; (4) the smaller the convergent angle, the greater the flow resistance; (5) FLUENT was highly accurate in predicting the empirical pressures of this model; (6) flow separation locations (given by FLUENT) for the divergent glottis moved upstream for larger flows and larger glottal angles. The results suggest that phonatory efficiency related to aerodynamics may be enhanced with vocal fold oscillations that include large convergent angles during glottal opening and small (5 degrees - 10 degrees) divergent angles during glottal closing.

The effects of the glottal geometry on intraglottal pressure distributions

The purpose of this study is to explore the effects of the glottal geometry on intraglottal and transglottal pressures using a Plexiglas model and a commercially computational fluid dynamics code, fluent. Nine glottal angles (uniform, as well as convergent and divergent 5, 10, 20, and 40 deg), 18 inferior vocal-fold angles varied from 87.5 to −10 deg, and 19 superior vocal-fold surface angles varied from −85 to 45 deg for uniform, convergen 10- and divergent 10-deg glottal angle, and a wide range of entrance radii varied from 0.26 to 0.005 cm for different divergent glottis were selected separately to examine their pressure distribution effects. The empirical data were supported by computational results using fluent. The results suggest that the 10-deg divergence angle may correspond to least flow resistance, the vocal-fold surface pressures are essentially independent of the inferior and superior vocal-fold surface angles realistic for human phonation, and a small glottal entrance radius tends to lower the transglottal pressure, move the minimal pressure near the glottal entrance more upstream, and make the pressure dip more negative in value. These results suggest that the glottal geometry should be well specified when using physical, mathematical phonatory models.

A three-dimensional model of vocal fold abduction/adduction.

A three-dimensional biomechanical model of tissue deformation was developed to simulate dynamic vocal fold abduction and adduction. The model was made of 1721 nearly incompressible finite elements. The cricoarytenoid joint was modeled as a rocking-sliding motion, similar to two concentric cylinders. The vocal ligament and the thyroarytenoid muscle's fiber characteristics were implemented as a fiber-gel composite made of an isotropic ground substance imbedded with fibers. These fibers had contractile and/or passive nonlinear stress-strain characteristics. The verification of the model was made by comparing the range and speed of motion to published vocal fold kinematic data. The model simulated abduction to a maximum glottal angle of about 31 degrees. Using the posterior-cricoarytenoid muscle, the model produced an angular abduction speed of 405 degrees per second. The system mechanics seemed to favor abduction over adduction in both peak speed and response time, even when all intrinsic muscle properties were kept identical. The model also verified the notion that the vocalis and muscularis portions of the thyroarytenoid muscle play significantly different roles in posturing, with the muscularis portion having the larger effect on arytenoid movement. Other insights into the mechanisms of abduction/adduction were given.

Pressure and velocity profiles in a static mechanical hemilarynx model

This study examined pressure and velocity profiles in a hemilarynx mechanical model of phonation. The glottal section was fabricated from hard plastic. Twelve pressure taps were mounted in the vocal-fold surface and connected to a differential pressure transducer through a pressure switch. The glottal gap was measured with a filter gauge and the glottal angle was well specified by use of a laser system. Eight pressure transducers were placed in the flat Plexiglas wall opposite the vocal fold. Hot-wire anemometry was used to obtain velocity profiles upstream and downstream of the glottis. The results indicate that the pressures were asymmetric in the glottis: the pressure distribution on the vocal fold was consistent with pressure change along a parallel duct, whereas the pressures on the opposite flat wall typically were lower. The upstream velocity profiles were symmetric regardless of the constriction shape and size. The jet velocity downstream of the glottis was turbulent even for laminar upstream conditions. The narrower the glottis, the closer the jet stayed to the upper wall and traveled further before expanding. The turbulence ratio was greater on the skirt of the jet and reached as high as 25% of the maximum jet velocity.

Laryngeal-respiratory kinematics are impaired in aged rats.

Fatigue and weakness in the elderly are the functional consequences of underlying neuromuscular decline. However, little is known about the manifestations of aging in the larynx. This study evaluated the manner in which laryngeal senescence affects laryngeal-respiratory kinematics by videorecording laryngeal motion in both young and old rats. Recorded images were digitized, and glottal displacement and movement rate were measured. The results indicated that the amplitude of change in glottal angle was significantly diminished, and laryngeal movement durations were prolonged in the old animals. These findings may be due to functional constraints on the respiratory system, impaired laryngeal-respiratory interactions, or decrements in vocal fold tension with age. Because of the serious and pervasive nature of dysphagia and communicative impairments in the elderly, research that specifically examines the manifestations and causes of these impairments is of great importance.

Intraglottal pressure profiles for a symmetric and oblique glottis with a divergence angle of 10 degrees.

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.

Flow visualization in a model of the glottis with a symmetric and oblique angle

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.]

Glottal pressure profiles for a diameter of 0.04 cm

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.]

Pressure profiles on the walls of the glottis for oblique glottal ducts

Oblique angles of the glottis occur during both normal and abnormal phonation. This study examined pressures on the glottal walls for a variety of oblique angle conditions. A Plexiglas model of the larynx was used to obtain wall pressures at 14 taps along the glottal surfaces. The model is 7.5 times larger than real life. A minimal diameter of 0.04 cm and duct axial length of 0.3 cm were used for all cases. Results indicated, for example, that for an included angle of 10 deg (divergence) and a transglottal pressure of 5-cm H2O, an oblique glottal angle of 15 deg compared to the symmetric glottis: (1) displaced the minimal wall pressure location on the divergent side a short distance downstream and on the convergent side to mid-glottis; (2) increased the pressure drop on the divergent side by about 15% and decreased the pressure drop on the convergent side by about 13%; and (3) broadened the minimum pressure dip on both the divergent and convergent sides. These results suggest paradoxical (opposite) driving pressures on the inferior glottal walls, which would enhance the nontypical phase differences between the two vocal folds. [Research support: NIH grant 1R01DC03577.]

Finite element simulation of glottal flow and pressure.

Computational studies of laryngeal aerodynamics should help clarify the relationships among configuration, air flow, surface pressure, and vocal fold movement within the larynx, and the acoustic consequences of the output glottal air flow. The penalty finite element method [S. W. Kim, Comput. Fluids 16(4), 429-444 (1988a); NASA CR-179357 (1988b); S. W. Kim and R. A. Decker, Int. J. Num. Meth. Fluids 9, 43-57 (1989)] was adopted to simulate steady air flow and air pressure through the larynx. A total of 133 conditions of different glottal configurations and inflow rates were studied. The computational results were compared to empirical data from earlier experiments. Two cases are reported (1) constant glottal divergence (42 degrees) but variable diameter and (2) constant glottal diameter (0.04 cm) but variable glottal angle. For case (1), the average discrepancy for translaryngeal pressure drop between the computational results and empirical data was 6.8% for pressures between 3 and 15 cm H2O. Flow separation occurred just downstream of the minimal glottal diameter. For case (2), the computational results for translaryngeal pressure drop differed from the empirically derived Scherer-Guo (S-G) equation predictions by an average of 8.9% for pressure between 3 and 13 cm H2O. Pressure recovery in the glottis suggested that the optimal glottal diffuser angle was near 10 degrees. Results suggest that the computational method should be sufficient to study glottal aerodynamics (assuming quasisteady flow).