Maximum Flow Declination Rate Research Articles

The Effects of Negative Pressure Induced by Flow Separation Vortices on Vocal Fold Dynamics during Voice Production.

This study used a two-dimensional flow-structure-interaction computer model to investigate the effects of flow-separation-vortex-induced negative pressure on vocal fold vibration and flow dynamics during vocal fold vibration. The study found that negative pressure induced by flow separation vortices enhances vocal fold vibration by increasing aeroelastic energy transfer during vibration. The result showed that the intraglottal pressure was predominantly negative after flow separation before gradually recovering to zero at the glottis exit. When the negative pressure was removed, the vibration amplitude and flow rate were reduced by up to 20%, and the closing speed, flow skewness quotient, and maximum flow declination rate were reduced by up to 40%. The study provides insights into the complex interactions between flow dynamics, vocal fold vibration, and energy transfer during voice production.

Anterior-posterior characterization of intraglottal flow fields in excised canine larynges

It has been espoused that intraglottal flow separation vortices (FSVs) play a critical role in the rapid closure of the vocal fold vibrations by acting as an additional pulling force that affects the maximum flow declination rate (MFDR). Clinically, MFDR is important because studies showed it highly correlates with loudness, intelligibility, and vocal efficiency. Previous studies that aimed to characterize the influence of FSVs were focused on their role in the mid-coronal plane. In the current study, particle imaging velocimetry was used to measure the intraglottal flow, specifically the FSVs, in the anterior–posterior aspects of the glottis during the closing phase of the vocal fold vibrations. The results show that the FSVs are extending along the length of the vocal fold in the anterior–posterior direction and that there is a direct relation between the size of FSVs and the magnitudes of the glottal divergence angles. The results also show that the centroid of FSVs occurs towards the anterior direction, where larger divergence angles are observed. These findings suggest that the FSVs in the anterior aspect have a more significant effect on the aerodynamic force acting on the glottal wall than the FSVs in the posterior aspect.

The influence of source-filter interaction on the voice source in a three-dimensional computational model of voice production.

The goal of this computational study is to quantify global effects of vocal tract constriction at various locations (false vocal folds, aryepiglottic folds, pharynx, oral cavity, and lips) on the voice source across a large range of vocal fold conditions. The results showed that while inclusion of a uniform vocal tract had notable effects on the voice source, further constricting the vocal tract only had small effects except for conditions of extreme constriction, at which constrictions at any location along the vocal tract decreased the mean and peak-to-peak amplitude of the glottal flow waveform. Although narrowing in the epilarynx increased the normalized maximum flow declination rate, vocal tract constriction in general slightly reduced the source strength and high-frequency harmonic production at the glottis, except for a limited set of vocal fold conditions (e.g., soft, long vocal folds subject to relatively high pressure). This suggests that simultaneous laryngeal and vocal tract adjustments are required to maximize source-filter interaction. While vocal tract adjustments are often assumed to improve voice production, our results indicate that such improvements are mainly due to changes in vocal tract acoustic response rather than improved voice production at the glottis.

Fluid-Structure Interaction Analysis of Aerodynamic and Elasticity Forces During Vocal Fold Vibration

The effect of the intraglottal vortices on the glottal flow waveform was explored using flow-structure-interaction (FSI) modeling. These vortices form near the superior aspect of the vocal folds during the closing phase of the folds' vibration. The geometry of the vocal fold was based on the well-known M5 model. The model did not include a vocal tract to remove its inertance effect on the glottal flow. Material properties for the cover and body layers of the folds were set using curve fit to experimental data of tissue elasticity. A commercially available FSI solver was used to perform simulations at low and high values of subglottal input pressure. Validation of the FSI results showed a good agreement for the glottal flow and the vocal fold displacement data with measurements taken in the excised canine larynx model. The simulations result further support the hypothesis that intraglottal vortices can affect the glottal flow waveform, specifically its maximum flow declination rate (MFDR). It showed that MFDR occurs at the same phase when the highest intraglottal vortical strength and the negative pressure occur. It also showed that when MFDR occurs, the magnitude of the aerodynamic force acting on the glottal wall is greater than the elastic recoil force predicted in the tissue. These findings are significant because nearly all theoretical and computational models that study the vocal fold vibrations mechanism do not consider the intraglottal negative pressure caused by the vortices as an additional closing force acting on the folds.

Lombard Effect in Individuals With Nonphonotraumatic Vocal Hyperfunction: Impact on Acoustic, Aerodynamic, and Vocal Fold Vibratory Parameters.

This exploratory study aims to investigate variations in voice production in the presence of background noise (Lombard effect) in individuals with nonphonotraumatic vocal hyperfunction (NPVH) and individuals with typical voices using acoustic, aerodynamic, and vocal fold vibratory measures of phonatory function. Nineteen participants with NPVH and 19 participants with typical voices produced simple vocal tasks in three sequential background conditions: baseline (in quiet), Lombard (in noise), and recovery (5 min after removing the noise). The Lombard condition consisted of speech-shaped noise at 80 dB SPL through audiometric headphones. Acoustic measures from a microphone, glottal aerodynamic parameters estimated from the oral airflow measured with a circumferentially vented pneumotachograph mask, and vocal fold vibratory parameters from high-speed videoendoscopy were analyzed. During the Lombard condition, both groups exhibited a decrease in open quotient and increases in sound pressure level, peak-to-peak glottal airflow, maximum flow declination rate, and subglottal pressure. During the recovery condition, the acoustic and aerodynamic measures of individuals with typical voices returned to those of the baseline condition; however, recovery measures for individuals with NPVH did not return to baseline values. As expected, individuals with NPVH and participants with typical voices exhibited a Lombard effect in the presence of elevated background noise levels. During the recovery condition, individuals with NPVH did not return to their baseline state, pointing to a persistence of the Lombard effect after noise removal. This behavior could be related to disruptions in laryngeal motor control and may play a role in the etiology of NPVH. https://doi.org/10.23641/asha.20415600.

Contribution of laryngeal size to differences between male and female voice production.

In this study we investigated the effect of sex- and age-related differences in vocal fold length, thickness, and depth on voice production in a three-dimensional vocal fold model. The results showed that the cause-effect relationships between vocal fold physiology and voice production previously identified in an adult male-like vocal fold geometry remained qualitatively the same in vocal folds with geometry representative of adult females and children. We further showed that the often-observed differences in voice production between adult males, adult females, and children can be explained by differences in length and thickness. The lower F0, higher flow rate, larger vocal fold vibration amplitude, and higher sound pressure level (SPL) in adult males as compared to adult females and children can be explained by differences in vocal fold length. In contrast, the thickness effect dominated and contributed to the larger closed quotient of vocal fold vibration, larger normalized maximum flow declination rate, and lower H1-H2 in adult males as compared to adult females and children. The effect of differences in vocal fold depth was generally small. When targeting a specific SPL, adult males experienced a lower peak vocal fold contact pressure during phonation than adult females and children.

Glottal Aerodynamics Estimated From Neck-Surface Vibration in Women With Phonotraumatic and Nonphonotraumatic Vocal Hyperfunction.

Purpose The purpose of this study was to determine whether estimates of glottal aerodynamic measures based on neck-surface vibration are comparable to those previously obtained using oral airflow and air pressure signals (Espinoza et al., 2017) in terms of discriminating patients with phonotraumatic and nonphonotraumatic vocal hyperfunction (PVH and NPVH) from vocally healthy controls. Method Consecutive /pae/ syllables at comfortable and loud level were produced by 16 women with PVH (organic vocal fold lesions), 16 women with NPVH (primary muscle tension dysphonia), and 32 vocally healthy women who were each matched to a patient according to age and occupation. Subglottal impedance-based inverse filtering of the anterior neck-surface accelerometer (ACC) signal yielded estimates of peak-to-peak glottal airflow, open quotient, and maximum flow declination rate. Average subglottal pressure and microphone-based sound pressure level (SPL) were also estimated from the ACC signal using subject-specific linear regression models. The ACC-based measures of glottal aerodynamics were normalized for SPL and statistically compared between each patient and matched-control group. Results Patients with PVH and NPVH exhibited lower SPL-normalized glottal aerodynamics values than their respective control subjects (p values ranging from < .01 to .07) with very large effect sizes (1.04-2.16), regardless of loudness condition or measurement method (i.e., ACC-based values maintained discriminatory power). Conclusions The results of this study demonstrate that ACC-based estimates of most glottal aerodynamic measures are comparable to those previously obtained from oral airflow and air pressure (Espinoza et al., 2017) in terms of differentiating between hyperfunctional (PVH and NPVH) and normal vocal function. ACC-based estimates of glottal aerodynamic measures may be used to assess vocal function during continuous speech and enables this assessment of daily voice use during ambulatory monitoring to provide better insight into the pathophysiological mechanisms associated with vocal hyperfunction.

Analysis of glottal inverse filtering in the presence of source-filter interaction

The validity of glottal inverse filtering (GIF) to obtain a glottal flow waveform from radiated pressure signal in the presence and absence of source-filter interaction was studied systematically. A driven vocal fold surface model of vocal fold vibration was used to generate source signals. A one-dimensional wave reflection algorithm was used to solve for acoustic pressures in the vocal tract. Several test signals were generated with and without source-filter interaction at various fundamental frequencies and vowels. Linear Predictive Coding (LPC), Quasi Closed Phase (QCP), and Quadratic Programming (QPR) based algorithms, along with supraglottal impulse response, were used to inverse filter the radiated pressure signals to obtain the glottal flow pulses. The accuracy of each algorithm was tested for its recovery of maximum flow declination rate (MFDR), peak glottal flow, open phase ripple factor, closed phase ripple factor, and mean squared error. The algorithms were also tested for their absolute relative errors of the Normalized Amplitude Quotient, the Quasi-Open Quotient, and the Harmonic Richness Factor. The results indicated that the mean squared error decreased with increase in source-filter interaction level suggesting that the inverse filtering algorithms perform better in the presence of source-filter interaction. All glottal inverse filtering algorithms predicted the open phase ripple factor better than the closed phase ripple factor of a glottal flow waveform, irrespective of the source-filter interaction level. Major prediction errors occurred in the estimation of the closed phase ripple factor, MFDR, peak glottal flow, normalized amplitude quotient, and Quasi-Open Quotient. Feedback-related nonlinearity (source-filter interaction) affected the recovered signal primarily when fo was well below the first formant frequency of a vowel. The prediction error increased when fo was close to the first formant frequency due to the difficulty of estimating the precise value of resonance frequencies, which was exacerbated by nonlinear kinetic losses in the vocal tract.

Quantification of the Intraglottal Pressure Induced by Flow Separation Vortices Using Large Eddy Simulation

The greatest rate of change in the glottal flow rate during phonation is a rapid decrease that occurs during the latter part of the glottal closing. Previous works showed that intraglottal flow separation vortices form in a divergent glottis, produce negative gauge pressures (below atmospheric) during closing. It is hypothesized here that flow separation vortices contribute to the rapid closing mechanism of the true vocal folds during phonation. Four idealized static models (M5) of the human larynx were investigated using large eddy simulation: 2 models featured parallel folds that did not enable flow separation in the glottis and 2 models involved a divergent glottis. The influence of the ventricular gap (narrow/wide) is evaluated. An unsteady pressure inlet representing a voicing cycle was applied to the sub-glottal region to mimic the time-varying glottal flow. Intraglottal vortex structures formed downstream of the separation point in a divergent glottis. Their existence caused a higher closing force that was applied onto the vocal folds. A narrow ventricular gap strengthens this effect. Strength of the intraglottal vortices increased with the maximum flow declination rate. Therefore, a more divergent shape of the glottis during glottal closing will be one of the main contributors to the voice quality.

Volume velocity in a canine larynx model using time‑resolved tomographic particle image velocimetry.

In the classic source-filter theory, the source of sound is flow modulation. "Flow" is the flow rate (Q) and flow modulation is dQ/dt. Other investigators have argued, using theoretical, computational, and mechanical models of the larynx, that there are additional sources of sound. To determine the acoustic role of dQ/dt in a tissue model, Q needs to be accurately measured within a few millimeters of the glottal exit; however, no direct measures of Q currently exist. The goal of this study is to obtain this waveform in an excised canine larynx model using time-resolved tomographic particle image velocimetry. The flow rate data are captured simultaneously with acoustic measurements to determine relations with vocal characteristics. The results show that glottal waveform characteristics such as maximum flow declination rate are proportional to the subglottal pressure, fundamental frequency, and acoustic intensity. These findings are important as they use direct measurements of the volume flow at the glottal exit to validate some of the assumptions used in the source-filter theory. In addition, future work will address the accuracy of indirect clinical measurement techniques, such as the Rothenberg mask.

An acoustic source model for asymmetric intraglottal flow with application to reduced-order models of the vocal folds.

The complex three-way interaction between airflow, tissue, and sound, for asymmetric vocal fold vibration, is not well understood. Current modeling efforts are not able to explain clinical observations where drastic differences in sound production are often observed, with no noticeable differences in the vocal fold kinematics. To advance this understanding, an acoustical model for voiced sound generation in the presence of asymmetric intraglottal flows is developed. The source model operates in conjunction with a wave reflection analog propagation scheme and an asymmetric flow description within the glottis. To enable comparison with prior work, the source model is evaluated using a well-studied two-mass vocal fold model. The proposed source model is evaluated through acoustic measures of interest, including radiated sound pressure level, maximum flow declination rate, and spectral tilt, and also via its effects on the vocal fold dynamics. The influence of the model, in comparison to the standard symmetric Bernoulli flow description, results in an increased transfer of energy from the fluid to the vocal folds, increased radiated sound pressure level and maximum flow declination rate, and decreased spectral tilt. These differences are most pronounced for asymmetric vocal fold configurations that mimic unilateral paresis and paralysis, where minor kinematic changes can result in significant acoustic and aerodynamic differences. The results illustrate that fluid effects arising from asymmetric glottal flow can play an important role in the acoustics of pathological voiced speech.

How modeling entrance loss and flow separation in a two-mass model affects the oscillation and synthesis quality

Self-oscillating bar-mass models of the vocal folds are frequently used as the voice source in articulatory speech synthesis. For these models, a number of ways to handle the entrance loss and the flow separation in the glottis have been proposed. However, the effect of different modeling choices on vocal fold oscillation and glottal flow, and on the quality of synthesized speech has been rarely examined. In this study, a modified two-mass model of the vocal folds was used to simulate phonation for 12 modeling options: three ways to model the entrance loss combined with four ways to model flow separation. For each condition, the following characteristics of the glottal oscillation and flow were determined: the phonation threshold pressure, the frequency range of self-sustained oscillation, the oscillation amplitude for different glottal rest openings, the spectral slope of the flow derivative, the maximum flow declination rate (MFDR), the open quotient (OQ), and the difference between the levels of the first and second harmonics of the flow derivative (H1-H2). In addition, the effect of the modeling options on the perceived naturalness of the synthetic voice was evaluated. There was no effect of the different ways to model entrance loss and flow separation on the phonation threshold pressure and on frequency range, and only a minor effect on MFDR, OQ, and H1-H2. However, there was a strong effect of the flow separation model on the oscillation amplitude, the spectral slope, and on the naturalness of the voice. The voice was perceived as most natural when the flow was assumed to always separate at the minimum glottal diameter.

Relationship between intraglottal geometry, vocal tract constriction, and glottal flow during phonation of a canine larynx

Hypothesis: The rapid reduction of the glottal volume flow rate, which usually occurs in normal phonation during the closing of the vocal folds, is measured by a quantity known as the maximum flow declination rate (MFDR). Our preliminary work highly suggests that intraglottal flow separation vortices (FSV), which form near the superior aspect of the divergent folds during closing, can directly affect MFDR. In this project, we hypothesize that the strength of the vortices is highly correlated with higher MFDR, larger divergence angles and stronger FSV. Methodology: We use particle image velocimetry to measure the strength of the FSV as well as the intraglottal pressures during phonation in four excised canine larynges with an attached mechanical vocal tract. Two vocal tract models are used, one with a false fold gap of 7 mm, one with a gap of 3 mm. Results: Stronger FSV (measured by vorticity) are correlated with glottic efficiency, larger glottal divergence angles and/or with decreased distance between the false folds. Conclusion: We show correlation of the strength of the FSV with different variables. These data are currently being used to validate computational flow structure models. These computational models then can be used to determine causation.

Advancement of flow velocity measurements in excised canine larynx model

In the classic source-filter model of speech production, flow modulation is the source of sound. Modulation of the flow refers to the fact that the volume flow, Q, is changing as the glottis opens and closes. Furthermore, studies have shown that the maximum flow declination rate (MFDR), which occurs during the latter part of the closing phase, is highly correlated with acoustic intensity (loudness) and acoustic energy in the higher harmonics. Therefore, measurements of the glottal airflow can provide important insights into voice mechanisms, dysfunction and efficiency. In recent years, particle image velocimetry (PIV) have become the method of choice for measuring Q because the technique can quantify, non-intrusively, the spatial and temporal information of the flow. The discussion includes progress of PIV measurements, from 2D to tomographic measurements, in the excised canine larynx model. Key findings related to intraglottal flow and glottal geometry, and their extension to modeling of voice mechanisms, are described.

Volume velocity field and acoustics measurements in a canine larynx model

In the classic source-filter theory, sound is produced at the glottis by a process known as flow modulation; in this case, “flow” specifically refers to the flow rate (Q) produced at the glottal exit during the phonation cycle. Flow modulation refers to the fact that Q is changing as the glottis opens and closes dQ/dt. Although dQ/dt is constantly changing from glottal opening and closing, the greatest rate of change happens during the latter part of closing, when Q rapidly decreases. This rapid deceleration is quantified by the maximum flow declination rate (MFDR). MFDR has been shown to highly correlate with acoustic intensity (loudness). The aim of this study is to measure changes in Q and the acoustic energy in a vibrating canine larynx model as a function of subglottal pressure and vocal tract constriction. Volume flow measurements are taken using time-resolved tomographic-PIV. Q at the glottal exit is extracted from PIV measurements and MFDR is computed from the waveform. Acoustic measurements (SPL) are taken simultaneously. Testing is done with and without vocal tract, which is place above the larynx. The constriction in the vocal tract is varied by changing the distance between the 2 false vocal folds (FVF). Each case above is tested at low and high subglottal pressures. Measurements show that the glottal exit flow is complex. The waveform of Q is skewed towards closing phase, even without a vocal tract. The skewing is affected further by the vocal tract constriction. Both MFDR and SPL increase with subglottal pressure.

Modeling the Pathophysiology of Phonotraumatic Vocal Hyperfunction With a Triangular Glottal Model of the Vocal Folds.

Our goal was to test prevailing assumptions about the underlying biomechanical and aeroacoustic mechanisms associated with phonotraumatic lesions of the vocal folds using a numerical lumped-element model of voice production. A numerical model with a triangular glottis, posterior glottal opening, and arytenoid posturing is proposed. Normal voice is altered by introducing various prephonatory configurations. Potential compensatory mechanisms (increased subglottal pressure, muscle activation, and supraglottal constriction) are adjusted to restore an acoustic target output through a control loop that mimics a simplified version of auditory feedback. The degree of incomplete glottal closure in both the membranous and posterior portions of the folds consistently leads to a reduction in sound pressure level, fundamental frequency, harmonic richness, and harmonics-to-noise ratio. The compensatory mechanisms lead to significantly increased vocal-fold collision forces, maximum flow-declination rate, and amplitude of unsteady flow, without significantly altering the acoustic output. Modeling provided potentially important insights into the pathophysiology of phonotraumatic vocal hyperfunction by demonstrating that compensatory mechanisms can counteract deterioration in the voice acoustic signal due to incomplete glottal closure, but this also leads to high vocal-fold collision forces (reflected in aerodynamic measures), which significantly increases the risk of developing phonotrauma.

Glottal Aerodynamic Measures in Women With Phonotraumatic and Nonphonotraumatic Vocal Hyperfunction.

The purpose of this study was to determine the validity of preliminary reports showing that glottal aerodynamic measures can identify pathophysiological phonatory mechanisms for phonotraumatic and nonphonotraumatic vocal hyperfunction, which are each distinctly different from normal vocal function. Glottal aerodynamic measures (estimates of subglottal air pressure, peak-to-peak airflow, maximum flow declination rate, and open quotient) were obtained noninvasively using a pneumotachograph mask with an intraoral pressure catheter in 16 women with organic vocal fold lesions, 16 women with muscle tension dysphonia, and 2 associated matched control groups with normal voices. Subjects produced /pae/ syllable strings from which glottal airflow was estimated using inverse filtering during /ae/ vowels, and subglottal pressure was estimated during /p/ closures. All measures were normalized for sound pressure level (SPL) and statistically tested for differences between patient and control groups. All SPL-normalized measures were significantly lower in the phonotraumatic group as compared with measures in its control group. For the nonphonotraumatic group, only SPL-normalized subglottal pressure and open quotient were significantly lower than measures in its control group. Results of this study confirm previous hypotheses and preliminary results indicating that SPL-normalized estimates of glottal aerodynamic measures can be used to describe the different pathophysiological phonatory mechanisms associated with phonotraumatic and nonphonotraumatic vocal hyperfunction.

Flow Glottogram and Subglottal Pressure Relationship in Singers and Untrained Voices

This article combines results from three earlier investigations of the glottal voice source during phonation at varying degrees of vocal loudness (1) in five classically trained baritone singers (Sundberg etal., 1999), (2) in 15 female and 14 male untrained voices (Sundberg etal., 2005), and (3) in voices rated as hyperfunctional by an expert panel (Millgård etal., 2015). Voice source data were obtained by inverse filtering. Associated subglottal pressures were estimated from oral pressure during the occlusion for the consonant /p/. Five flow glottogram parameters, (1) maximum flow declination rate (MFDR), (2) peak-to-peak pulse amplitude, (3) level difference between the first and the second harmonics of the voice source, (4) closed quotient, and (5) normalized amplitude quotient, were averaged across the singer subjects and related to associated MFDR values. Strong, quantitative relations, expressed as equations, are found between subglottal pressure and MFDR and between MFDR and each of the other flow glottogram parameters. The values for the untrained voices, as well as those for the voices rated as hyperfunctional, deviate systematically from the values derived from the equations.

Influence of Left-Right Asymmetries on Voice Quality in Simulated Paramedian Vocal Fold Paralysis.

The purpose of this study was to determine the vocal fold structural and vibratory symmetries that are important to vocal function and voice quality in a simulated paramedian vocal fold paralysis. A computational kinematic speech production model was used to simulate an exemplar "voice" on the basis of asymmetric settings of parameters controlling glottal configuration. These parameters were then altered individually to determine their effect on maximum flow declination rate, spectral slope, cepstral peak prominence, harmonics-to-noise ratio, and perceived voice quality. Asymmetry of each of the 5 vocal fold parameters influenced vocal function and voice quality; measured change was greatest for adduction and bulging. Increasing the symmetry of all parameters improved voice, and the best voice occurred with overcorrection of adduction, followed by bulging, nodal point ratio, starting phase, and amplitude of vibration. Although vocal process adduction and edge bulging asymmetries are most influential in voice quality for simulated vocal fold motion impairment, amplitude of vibration and starting phase asymmetries are also perceptually important. These findings are consistent with the current surgical approach to vocal fold motion impairment, where goals include medializing the vocal process and straightening concave edges. The results also explain many of the residual postoperative voice limitations.

Sensitivity of Source-Filter Interaction to Specific Vocal Tract Shapes.

A systematic variation of length and cross-sectional area of specific segments of the vocal tract (trachea to lips) was conducted computationally to quantify the effects of source-filter interaction. A one-dimensional Navier-Stokes (transmission line) solution was used to compute peak glottal airflow, maximum flow declination rate, and formant ripple on glottal flow for Level 1 (aero-acoustic) interactions. For Level 2 (tissue movement) interaction, peak glottal area, phonation threshold pressure, and deviation in fo were quantified. Results show that the ventricle, the false-fold glottis, the conus elasticus entry, and the laryngeal vestibule are the regions to which acoustic variables are most sensitive. Generally, any narrow section of the vocal tract increases the degree of interaction, both in terms of its length and its cross-sectional area. The closer the narrow section is to the vocal folds, the greater the effect.