Phonatory Cycle Research Articles

Mapping Phonation Types by Clustering of Multiple Metrics

For voice analysis, much work has been undertaken with a multitude of acoustic and electroglottographic metrics. However, few of these have proven to be robustly correlated with physical and physiological phenomena. In particular, all metrics are affected by the fundamental frequency and sound level, making voice assessment sensitive to the recording protocol. It was investigated whether combinations of metrics, acquired over voice maps rather than with individual sustained vowels, can offer a more functional and comprehensive interpretation. For this descriptive, retrospective study, 13 men, 13 women, and 22 children were instructed to phonate on /a/ over their full voice range. Six acoustic and EGG signal features were obtained for every phonatory cycle. An unsupervised voice classification model created feature clusters, which were then displayed on voice maps. It was found that the feature clusters may be readily interpreted in terms of phonation types. For example, the typical intense voice has a high peak EGG derivative, a relatively high contact quotient, low EGG cycle-rate entropy, and a high cepstral peak prominence in the voice signal, all represented by one cluster centroid that is mapped to a given color. In a transition region between the non-contacting and contacting of the vocal folds, the combination of metrics shows a low contact quotient and relatively high entropy, which can be mapped to a different color. Based on this data set, male phonation types could be clustered into up to six categories and female and child types into four. Combining acoustic and EGG metrics resolved more categories than either kind on their own. The inter- and intra-participant distributional features are discussed.

Impact of subclinical mental disorders of voice function and quality of life in voice-speaking professions during the COVID-2019 pandemic

Objective: To investigate the risk of mental distress during the COVID-19 pandemic in individuals of the voice-speech professions and the possibility of its impact on voice function and quality of life. Materials and Methods: The study involved 33 people of voice-speech professions who were treated at the University Clinic of Zaporizhzhia State Medical University in 2020. The presence of mental disorders was determined by questionnaires using the hospital anxiety and depression scale (HADS). The patients were divided into 2 groups, depending on the absence and presence of significantly expressed symptoms. A specialized phoniatric examination using functional loads (measuring the time of maximum phonation (PMF), perceptual assessment of the voice according to the GRBAS scale), videostroboscopy of the larynx were carried out. The assessment of the mental impact of voice disorders on the quality of life was carried out according to the Voice Handicap Index (VHI) questionnaire. The statistical significance of the comparative indicators and the connection of their changes were established using the Spearman's rank correlation coefficient. Results: It was found that among the surveyed 33 people, 22 patients (group 1) had subclinical anxiety and depression, and 11 (group 2) had no significant symptoms. Patients with subclinically severe mental disorders (n = 22) showed a significant increase in the emotional indicator by 85.37% (p≤0.01). A high positive relationship was found between subclinical levels of anxiety and depression and disturbances in the phonatory cycle of the larynx. When conducting a Spearman correlation analysis between the data of perceptual assessment of the voice according to the GRBAS system, data of video stroboscopy of the larynx, indicators of anxiety and depression, and the results of the VHI questionnaire, a positive relationship of a high degree was established between the level of anxiety and vibratory insufficiency of the vocal folds (rs=0.95; p≤0.05), negative with the Navy (rs=-0.59; p≤0.05), as well as physical (rs=0.75; p≤0.05) and emotional (rs=0.79; p≤0.05) components of average quality of life. The data obtained indicate a significant effect of subclinical disorders of the mental state on impaired voice function and the emotional component of the quality of life in persons of vocal-speech professions. Conclusions: Screening of mental health in persons of voice-speech professions together with a baseline assessment of voice function and quality of life are important steps for monitoring potential voice disorders and the formation of risk groups in order to carry out preventive and therapeutic measures for voice disorders.

Direct measurement and modeling of intraglottal, subglottal, and vocal fold collision pressures during phonation in an individual with a hemilaryngectomy.

The purpose of this paper is to report on the first in vivo application of a recently developed transoral, dual-sensor pressure probe that directly measures intraglottal, subglottal, and vocal fold collision pressures during phonation. Synchronous measurement of intraglottal and subglottal pressures was accomplished using two miniature pressure sensors mounted on the end of the probe and inserted transorally in a 78-year-old male who had previously undergone surgical removal of his right vocal fold for treatment of laryngeal cancer. The endoscopist used one hand to position the custom probe against the surgically medialized scar band that replaced the right vocal fold and used the other hand to position a transoral endoscope to record laryngeal high-speed videoendoscopy of the vibrating left vocal fold contacting the pressure probe. Visualization of the larynx during sustained phonation allowed the endoscopist to place the dual-sensor pressure probe such that the proximal sensor was positioned intraglottally and the distal sensor subglottally. The proximal pressure sensor was verified to be in the strike zone of vocal fold collision during phonation when the intraglottal pressure signal exhibited three characteristics: an impulsive peak at the start of the closed phase, rounded peak during the open phase, and minimum value around zero immediately preceding the impulsive peak of the subsequent phonatory cycle. Numerical voice production modeling was applied to validate model-based predictions of vocal fold collision pressure using kinematic vocal fold measures. The results successfully demonstrated feasibility of in vivo measurement of vocal fold collision pressure in an individual with a hemilaryngectomy, motivating ongoing data collection that is designed to aid in the development of vocal dose measures that incorporate vocal fold impact collision and stresses.

Physics of phonation offset: Towards understanding relative fundamental frequency observations.

Relative fundamental frequency (RFF) is a promising assessment technique for vocal pathologies. Herein, we explore the underlying laryngeal factors dictating RFF behaviours during phonation offset. To gain physical insights, we analyze a simple impact oscillator model and follow that with a numerical study using the well-established body-cover model of the vocal folds (VFs). Study of the impact oscillator suggests that the observed decrease in fundamental frequency during offset is due, at least in part, to the increase in the neutral gap between the VFs during abduction and the concomitant decrease in collision forces. Moreover, the impact oscillator elucidates a correlation between sharper drops in RFF and increased stiffness of the VFs, supporting experimental RFF studies. The body-cover model study further emphasizes the correlation between the drops in RFF and collision forces. The numerical analysis also illustrates the sensitivity of RFF to abduction initiation time relative to the phase of the phonation cycle, and the abduction period length. In addition, the numerical simulations display the potential role of the cricothyroid muscle to mitigate the RFF reduction. Last, simplified models of phonotraumatic vocal hyperfunction are explored, demonstrating that the observed sharper drops in RFF are associated with increased pre-offset collision forces.

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.

Esophageal aerodynamics in an idealized experimental model of tracheoesophageal speech

Flow behavior is investigated in the esophageal tract in an idealized experimental model of tracheoesophageal speech. The tracheoesophageal prosthesis is idealized as a first-order approximation using a straight, constant diameter tube. The flow is scaled according to Reynolds, Strouhal, and Euler numbers to ensure dynamic similarity. Flow pulsatility is produced by a driven orifice that approximates the kinematics of the pharyngoesophageal segment during tracheoesophageal speech. Particle image velocimetry data are acquired in three orthogonal planes as the flow exits the model prosthesis and enters the esophageal tract. Contrary to prior investigations performed in steady flow with the prosthesis oriented in-line with the flow direction, the fluid dynamics are shown to be highly unsteady, suggesting that the esophageal pressure field will be similarly complex. A large vortex ring is formed at the inception of each phonatory cycle, followed by the formation of a persistent jet. This vortex ring appears to remain throughout the entire cycle due to the continued production of vorticity resulting from entrainment between the prosthesis jet and the curved esophageal walls. Mean flow in the axial direction of the esophagus produces significant stretching of the vortex throughout the phonatory cycle. The stagnation point created by the jet impinging on the esophageal wall varies throughout the cycle due to fluctuations in the jet trajectory, which most likely arises due to flow separation within the model prosthesis. Applications to tracheoesophageal speech, including shortcomings of the model and proposed future plans, are discussed.

A study on the effect of intraglottal vortical structures on vocal fold vibration

Recent investigations suggested possible formation of the vortical structures in the intraglottal region during the closing phase of the phonation cycle. Vortical regions in the flow field are locations of negative pressure, and it has been hypothesized that this negative pressure might facilitate the glottal closure and thus affects the vibration pattern and voice production for high subglottal pressures. However, it is unclear whether the vortex-induced negative pressure is large enough, compared with vocal fold inertia and elastic recoil, to have a noticeable effect on glottal closure. In addition, the intraglottal vortical structures generally exist only for a small fraction of the closing phase when the glottis becomes divergent enough to induce flow separation. In the current work, oscillation of the vocal folds and the flow field are modeled using a non-linear finite element solver and a reduced order flow solver, respectively. The effect of vortical structures is modeled as a sinusoidal negative pressure wave applied to vocal fold surface between the flow separation point and the superior edge of the vocal folds. The effects of this vortex-induced negative pressure are quantified at different conditions of vocal fold stiffness and subglottal pressures. [Work supported by NIH.]

Quantification of the false vocal-folds effects on the intra-glottal pressures using large eddy simulation

During the closing phase of the phonation cycle the true vocal-folds (TVF) have a convergent-divergent shape. The negative pressures generated by the flow through the glottal passage are producing closing forces acting on the TVFs towards the center of the larynx. Intra-glottal pressures can affect both vocal-fold vibration and voice production, since they can accelerate the closing phase. This has a positive impact on the voice quality. Large Eddy Simulation approach is used to investigate the intra-glottal forces generated solely by the flow during the closing phase. The influence of the gap between the false vocal-folds (FVFs) and the location of FVFs with respect to the TVFs are analyzed. Based on anatomical measurements, four different gaps between the FVFs and two different distances between the true and false vocal-folds are investigated for the same trans-laryngeal pressure. The TVFs gap is kept constant. All cases exhibit a non-symmetric flow behavior in the mid-frontal plane. As compared with the baseline, significant negative pressures were found acting on the TVFs when the false glottal width is below a certain threshold value. The closing forces are increasing when the FVFs are located at larger distances further downstream from the TVFs.

Three-dimensional laryngeal flow fields induced by a model vocal fold polyp

Pathological laryngeal flow fields are investigated in a dynamically-driven, scaled-up model of the vocal folds. Disruption of the flow field due to the presence of a geometric protuberance, representative of a sessile unilateral polyp, is investigated in both the streamwise and transverse flow directions using phase-averaged particle image velocimetry. It is shown that the protuberance disrupts the normal flow behavior of the glottal jet throughout the phonatory cycle. During the divergent portions of the glottal cycle, the flow is characterized by the formation of hairpin vortices downstream of the protuberance. The protuberance also introduces significant velocity gradients in the anterior-posterior direction, which cover ∼30−40% of the vocal fold length. It is proposed that the disruption of the normal velocity behavior owing to the presence of a polyp will adversely impact the aerodynamic loadings that drive vocal fold motion, contributing to the temporal and spatial vocal fold asymmetries that are clinically-observed in patients with unilateral polyps.

Dynamics of temporal variations in phonatory flow.

This paper addresses the dynamic relevance of time variations of phonatory airflow, commonly neglected under the quasisteady phonatory flow assumption. In contrast to previous efforts, which relied on direct measurement of glottal impedance, this work uses spatially and temporally resolved measurements of the velocity field to estimate the unsteady and convective acceleration terms in the unsteady Bernoulli equation. Theoretical considerations suggest that phonatory flow is inherently unsteady when two related conditions apply: (1) that the unsteady and convective accelerations are commensurate, and (2) that the inertia of the glottal jet is non-negligible. Acceleration waveforms, computed from experimental data, show that unsteady and convective accelerations to be the same order of magnitude, throughout the cycle, and that the jet flow contributes significantly to the unsteady acceleration. In the middle of the cycle, however, jet inertia is negligible because the convective and unsteady accelerations nearly offset one another in the jet region. These results, consistent with previous findings treating quasisteady phonatory flow, emphasize that unsteady acceleration cannot be neglected during the final stages of the phonation cycle, during which voice sound power and spectral content are largely determined. Furthermore, glottal jet dynamics must be included in any model of phonatory airflow.

Dynamic imaging of vocal fold oscillation with four-dimensional optical coherence tomography

Optical coherence tomography (OCT) can provide high-resolution ( approximately 10-15 microm/pixel) images of vocal fold microanatomy, as demonstrated previously. We explored physiologically triggered Fourier-domain OCT for imaging vocal folds during phonation. The goal is to visualize dynamic histological cross sections and four-dimensional data sets where multiple planes are displayed in synchronized motion. If feasible, this approach could be a useful research tool and spur development of new clinical instrumentation. A Fourier-domain, triggered OCT system was created and tested in experiments on excised calf larynges to obtain preliminary observations and characterize important factors affecting image quality. Larynges were imaged during phonation driven by warm, humidified air. A subglottal pressure signal was used to synchronize the OCT system with the phonatory cycle. Image sequences were recorded as functions of anatomical location or subglottal pressure. Implant materials were also imaged during vibration, both in isolation and after injection into a vocal fold. Oscillations of epithelium and lamina propria were observed, and parameters such as shape, amplitude, and velocity of the vocal fold mucosal waves were found to be measurable. Ripples of mucosal wave as small as 100 microm in vertical height were clearly visible. Internal strain was also observed in normal and implanted vocal folds. Four-dimensional OCT of the vocal fold may help to more directly relate biomechanics to anatomy and disease. It may also be useful for assaying the functional rheology of implants in the context of real tissue. With further development, this technology has potential for clinical endoscopic application.

Viscous flow features in scaled-up physical models of normal and pathological vocal phonation

Unilateral vocal fold paralysis results when the recurrent laryngeal nerve, which innervates the muscles of the vocal folds becomes damaged. The loss of muscle and tension control to the damaged vocal fold renders it ineffectual. The mucosal wave disappears during phonation, and the vocal fold becomes largely immobile. The influence of unilateral vocal fold paralysis on the viscous flow development, which impacts speech quality within the glottis during phonation was investigated. Driven, scaled-up vocal fold models were employed to replicate both normal and pathological patterns of vocal fold motion. Spatial and temporal velocity fields were captured using particle image velocimetry, and laser Doppler velocimetry. Flow parameters were scaled to match the physiological values associated with human speech. Loss of motion in one vocal fold resulted in a suppression of typical glottal flow fields, including decreased spatial variability in the location of the flow separation point throughout the phonatory cycle, as well as a decrease in the vorticity magnitude.

An investigation of asymmetric flow features in a scaled-up driven model of the human vocal folds

Flow through a driven, 7.5 times life-size vocal fold model was investigated at corresponding life-size flow rates of Q mean = 89.1 ml/s, 159.4 ml/s, and 253.0 ml/s. The flow was scaled to match physiological values for Reynolds, Strouhal, and Euler numbers. The models were driven at a life-size frequency of 94 Hz. Particle image velocimetry (PIV) data were acquired in the anterior–posterior midplane of the glottis, and the unsteady transglottal pressure drop across the vocal folds was simultaneously measured. Flow and pressure data were obtained at four discrete instances during the closing phases of the phonatory cycle for which t/T open = 0.60, 0.70, 0.80, and 0.90. The glottal jet trajectory exhibited a bimodal distribution of flow attachment between the two medial surfaces of the glottis. Vortex shedding at the trailing edge separation point generated instabilities in the shear layer, which caused large oscillations in the glottal jet orientation downstream of the glottal exit. The development of the Coanda effect during the glottal cycle was found to have minimal impact on the transglottal pressure drop, suggesting that flow orientation does not directly influence the dipole sound source. The change in transglottal pressure drop as a result of jet trajectory was less than 2% for all three investigated flow rates.

Source‐filter interaction in the opposite direction: Subglottal coupling and the influence of vocal fold mechanics on vowel spectra during the closed phase.

Studies of speech source-filter interaction usually investigate the effect of the speech transfer function (loading) on vocal fold vibration and the voice source. In this study we explore how vocal fold mechanics affect the transfer function throughout the glottal cycle, with emphasis on the closed phase. Coupling between the subglottal and supraglottal airways is modulated by the laryngeal impedance. Although coupling is generally thought to occur only during the open phase of vocal fold vibration, a posterior glottal opening and the vocal fold tissue itself can allow sound transmission, thereby introducing coupling during the closed phase as well. The impedance of the vocal fold tissue at closure is shown to be small enough to permit coupling throughout the phonatory cycle, even in the absence of a posterior glottal opening. Open- and closed-phase coupling is characterized using mathematical models of the subglottal and supraglottal airways, and the parallel laryngeal impedances of the membranous glottis, posterior glottal opening, and vocal fold tissue. Examples from sustained vowels are presented, using synchronous recordings of neck skin acceleration, laryngeal high-speed videoendoscopy, electroglottography, and radiated acoustic pressure.

Low-dimensional models of the glottal flow incorporating viscous-inviscid interaction

The behavior of glottal flow can, to a large extent, be characterized by development and separation of the boundary layer. The point of flow separation is known to vary during the phonatory cycle due to change in channel configuration. To take the movable nature of the separation point into account, the boundary-layer equation is solved numerically, and the values of the characteristic quantities are determined as well as the point of separation. Development of the boundary layer in general reduces the effective size of the channel, and, therefore, increases the core flow velocity, which, in turn provides the boundary condition of the boundary-layer equation. The interaction between the viscous (boundary layer) and inviscid (core flow) parts of the glottal flow is, therefore, strongly indicated. To apply this viscous-inviscid interaction, the expression of the core flow is derived for a two-dimensional flow field, and is solved jointly with the boundary-layer equation. Numerical results are shown to examine the effect of the Reynolds number and glottal configuration, with special emphasis on the comparison of flow models developed for one- and two-dimensional flow fields. Numerical results are also quantitatively compared with data obtained from flow measurement experiments.

Characterization of the airflow through a scaled physical vocal fold model with a unilateral polyp.

The formation of vocal fold polyps, caused by trauma, interferes with normal speech, causing hoarseness or breathiness during phonation. The objective of this study is to investigate the disruption of the glottal flow field due to the presence of a unilateral vocal fold polyp. An ellipsoidal polyp was molded using silicone and incorporated onto the right medial surface of a driven, 7.5 times physiological size vocal fold model. Particle image velocimetry was used to observe the air flow through the vocal folds along a coronal section at discrete phases of the phonatory cycle. Air flow was scaled to match physiological values of Reynolds, Strouhal, and Euler numbers. Data were acquired in planes bisecting the polyp and others offset anterior and posterior to the center of the polyp, in order to ascertain any three‐dimensionality of the disrupted flow. The resulting velocity measurements and transglottal pressure drops were compared to previous results from normal vocal fold motion. Differences in flow char...

Unsteady laryngeal airflow simulations: An analysis of the generated intraglottal vortical structures.

Unsteady flow simulations in diffuserlike vocal‐fold models proved that laryngeal airflow generates vortical structures in the intraglottal region. However, the features of these vortices and their influence on the vocal‐fold motion were not clearly addressed. The present work characterizes the intraglottal vortical structures developed during the closing phase of the phonation cycle in order to analyze their possible influence on the voice quality. It is shown that intraglottal vortices are formed on the divergent slope of the glottis, just downstream of the separation point. The core of the vortical structures is characterized by important negative static pressure values (lower as compared with the surrounding pressure field). These vortices gain strength and increase in size as are convected downstream by the flow. The mechanism for which the intraglottal flow structures are becoming stronger is attributed to the entrained air from the supraglottal region. The instantaneous pressure loads on the divergent glottal slope are not uniform (in both time and space) and dependent on the vortical structures traveling nearby the glottis. The negative static pressures associated with the intraglottal vortical structures suggest that the closing phase during phonation may be accelerated by such vortices.

On the influence of vocal fold collision on phonation

For laryngoscopic observations show that the closed time of the glottis is significantly long, especially for low‐frequency vocal fold vibrations in the vocal fry and chest register. Vocal fold contact appears to be a major part of the phonatory cycle and may play an important role for self‐sustained vocal fold oscillations. Using a 2D, finite element, self‐oscillating model of the coupled vocal fold‐glottal flow system, we studied the influence of the mechanical impact on phonation onset mechanisms and vocal fold vibratory behavior. The air flow was assumed to be laminar and the compressible Navier‐Stokes equations were solved for the flow domain. For fixed values of the Young's modulus of the vocal fold we found that vocal fold contact significantly increased the vibration frequency as compared to the case of no contact. The changed total pressure forces on the vocal fold in medial‐lateral (lift force) and inferior‐superior (drag force) directions resulted in different phonation threshold pressure values and vocal fold vibration patterns. The increase in phonation frequency due to contact will be discussed based on the theory of impact oscillators.

Using Particle Imaging Velocimetry to Measure Anterior-Posterior Velocity Gradients in the Excised Canine Larynx Model

To quantify the anterior-posterior velocity gradient, we studied the velocity flow fields above the vocal folds in both the midcoronal and midsagittal planes. It was also our purpose to use these fields to deduce the mechanisms that cause the anterior-posterior gradient and to determine whether the vortical structures are highly 3-dimensional. Using the particle imaging velocimetry method for 5 excised canine larynges, we obtained phase-averaged velocity fields in the midcoronal and midsagittal planes for 30 phases of phonation. The velocity fields were determined synchronously with the vocal fold motion recorded by high-speed videography. The results show that immediately above the folds, there is no significant anterior-posterior velocity gradient. However, as the flow travels downstream, the laryngeal jet tends to narrow in width and skew toward the anterior commissure. Vortices are seen at the anterior and posterior edges of the flow. The downstream narrowing in the midsagittal plane is consistent with and is probably due to a phenomenon known as axis switching. Axis switching also involves vortices in the sagittal and coronal planes bending in the axial plane. This results in highly 3-dimensional, complex vortical structures. However, there is remarkable cyclic repeatability of these vortices during a phonation cycle.

Vortical Flow Field during Phonation in an Excised Canine Larynx Model

To more fully understand the mechanisms of vocal fold vibration and sound production, we studied the velocity flow fields above the folds. Such velocity fields during phonation have not been reported in the literature. Using the particle image velocimetry method for 3 excised canine larynges, we obtained the velocity fields in the mid-membranous coronal plane during different phases of phonation. The velocity field was determined synchronously with the vocal fold motion recorded by high-speed videography. The results show that vortices occur immediately above the vocal folds and that the location and shape of the vortices depend on the phase of the phonation cycle. Consistent vortical structures found included starting vortices, Kelvin-Helmholtz vortices, entrainment vortices, and vortices directly above the folds during the divergent glottal stage. These vortical structures were consistently found during specific phases of the glottal cycle for 3 canine larynges that significantly varied in size. This consistent behavior suggests that the vortices may be important for both vibration and sound production; however, further study is needed to prove this. The clinical significance of these vortices is discussed.