Irregular Vocal Fold Vibration Research Articles

Examining the Quasi-Steady Airflow Assumption in Irregular Vocal Fold Vibration

The quasi-steady flow assumption (QSFA) is commonly used in the field of biomechanics of phonation. It approximates time-varying glottal flow with steady flow solutions based on frozen glottal shapes, ignoring unsteady flow behaviors and vocal fold motion. This study examined the limitations of QSFA in human phonation using numerical methods by considering factors of phonation frequency, air inertance in the vocal tract, and irregular glottal shapes. Two sets of irregular glottal shapes were examined through dynamic, pseudo-static, and quasi-steady simulations. The differences between dynamic and quasi-steady/pseudo-static simulations were measured for glottal flow rate, glottal wall pressure, and sound spectrum to evaluate the validity of QSFA. The results show that errors in glottal flow rate and wall pressure predicted by QSFA were small at 100 Hz but significant at 500 Hz due to growing flow unsteadiness. Air inertia in the vocal tract worsened predictions when interacting with unsteady glottal flow. Flow unsteadiness also influenced the harmonic energy ratio, which is perceptually important. The effects of glottal shape and glottal wall motion on the validity of QSFA were found to be insignificant.

Effect of Controlled Muscle Activation in a Unilateral Vocal Fold Polyp Setting on Vocal Fold Vibration

Unilateral vocal fold polyps can lead to incomplete glottal closure and irregular vocal fold vibration. Depending on polyp size and resulting dysphonia severity, voice therapy or surgery may be recommended. As part of voice therapy, patients may learn how to optimize intrinsic and extrinsic laryngeal muscle use to mitigate benign lesion effects, increase vocal efficiency, and improve voice quality. In this study, we used a low-dimensional mass model with a simulated unilateral vocal fold polyp and varied intra-laryngeal muscle activity to simulate vocal fold vibration across varied conditions. Differing muscle activation has different effects on frequency, periodicity, and intensity. Accordingly, learning how to optimize muscle activity in a unilateral polyp setting may help patients achieve the best possible periodic and most efficiently produced voice in the context of abnormal vocal fold morphology.

Mechanisms of sound production in deer mice (Peromyscus spp.).

Rodent diversification is associated with a large diversity of species-specific social vocalizations generated by two distinct laryngeal sound production mechanisms: whistling and airflow-induced vocal fold vibration. Understanding the relative importance of each modality to context-dependent acoustic interactions requires comparative analyses among closely related species. In this study, we used light gas experiments, acoustic analyses and laryngeal morphometrics to identify the distribution of the two mechanisms among six species of deer mice (Peromyscus spp.). We found that high frequency vocalizations (simple and complex sweeps) produced in close-distance contexts were generated by a whistle mechanism. In contrast, lower frequency sustained vocalizations (SVs) used in longer distance communication were produced by airflow-induced vocal fold vibrations. Pup isolation calls, which resemble adult SVs, were also produced by airflow-induced vocal fold vibrations. Nonlinear phenomena (NLP) were common in adult SVs and pup isolation calls, suggesting irregular vocal fold vibration characteristics. Both vocal production mechanisms were facilitated by a characteristic laryngeal morphology, including a two-layered vocal fold lamina propria, small vocal membrane-like extensions on the free edge of the vocal fold, and a singular ventral laryngeal air pocket known as the ventral pouch. The size and composition of vocal folds (rather than total laryngeal size) appears to contribute to species-specific acoustic properties. Our findings suggest that dual modes of sound production are more widespread among rodents than previously appreciated. Additionally, the common occurrence of NLP highlights the nonlinearity of the vocal apparatus, whereby small changes in anatomy or physiology trigger large changes in behavior. Finally, consistency in mechanisms of sound production used by neonates and adults underscores the importance of considering vocal ontogeny in the diversification of species-specific acoustic signals.

On the significance of three-dimensional imaging for interpreting vocal fold dynamics

Physical mechanisms of regular and irregular vocal fold vibration were first studied in a finite element model of vocal fold vibration using the method of empirical eigenfunctions. Later the same method was used to successfully study physical mechanisms of vocal fold vibration in laboratory hemilarynx experiments (in which the medial surface of vocal fold was imaged). In subsequent clinical studies, however, the method exhibited significantly less interpretive power, presumably because of the limitations imposed by imaging from a 2D superior view. Our hypothesis is that the interpretive power of the method of empirical eigenfunctions will be significantly enhanced in clinical settings if 3D imaging is used instead of 2D imaging. To test this hypothesis, the method of empirical eigenfunctions was employed on the same finite element model implemented previously, as dynamical information was systematically removed from the analysis (interior tissue dynamics, medial surface dynamics, vertical dynamics of the superior surface, etc.). The natural modes of vibration were re-computed at each stage, and the deformations from the original natural modes were observed. The results suggest that in clinical settings, the method of empirical eigenfunctions retains significant interpretive power regarding physical mechanisms of irregular vibration when 3D imaging is used.

Impact of the Paraglottic Space on Voice Production in an MRI-Based Vocal Fold Model

While the vocal fold is in direct contact anteriorly with the thyroid cartilage, posteriorly the vocal fold connects to the thyroid cartilage through a soft tissue layer in the paraglottic space. Currently the paraglottic space is often neglected in computational models of phonation, in which a fixed boundary condition is often imposed on the lateral surface of the vocal fold. The goal of this study was to investigate the effect of the paraglottic space on voice production in an MRI-based vocal fold model, and how this effect may be counteracted by vocal fold stiffening due to laryngeal muscle activation. Parametric simulation study using an MRI-based computational vocal fold model. The results showed that the presence of the paraglottic space increased the mean and amplitude of the glottal area waveform, decreased the phonation frequency and closed quotient. For the particular vocal fold geometry used in this study, the presence of the paraglottic space also reduced the occurrence of irregular vocal fold vibration. These effects of the paraglottic space became smaller with increasing paraglottic space stiffness and to a lesser degree with vocal fold stiffening. The results suggest that the paraglottic space may be neglected in qualitative evaluations of normal phonation, but needs to be included in simulations of pathological phonation or vocal fold posturing.

Videolaryngostroboscopy in early vocal fold carcinoma diagnosis

Introduction/Objective. Vocal folds are the most common primary site of laryngeal carcinoma. Advancement in diagnostic and therapeutic modalities have provided better prognosis for patients with early glottic carcinoma. We aimed to report the role of videolaryngostroboscopy (VLS) in early diagnosis of vocal fold carcinoma. Methods. Prospective controlled study included 300 dysphonic patients admitted to the tertiary medical center for microlaryngoscopy with biopsy. All patients underwent stroboscopic examination prior to biopsy. VLS findings were classified according to Hirano into four stages, with an adynamic vocal fold segment and absence of vocal fold vibration, suspected for vocal fold carcinoma at stage IV. Histopathological findings have been graded according to Ljubljana classification into simple hyperplasia, abnormal hyperplasia, atypical hyperplasia, and carcinoma in situ. Results. Analysis of VLS findings showed that 41.67% of patients (n = 125/300) had asymmetrical and irregular vocal fold vibration with a mucosal wave reduction (VLS stage III), while an adynamic vocal fold segment and absence of vocal fold vibration (VLS stage IV), suspected for vocal fold carcinoma, was noticed in 17.33% of patients (n = 52/300). Histopathology report showed that vocal fold carcinoma was verified in 5.6% of patients in VLS stage III (n = 7/125), while VLS stage IV carcinoma was detected in 26.92% of patients (n = 14/52). Adynamic segment or entire nonvibrating vocal fold finding predicts early glottic carcinoma with a sensitivity of 66.77%, specificity of 86.4%, and moderate diagnostic accuracy (AUC = 0.844). Conclusion. VLS plays an important role as a timely indicator for microlaryngoscopy with biopsy in diagnosis of vocal fold carcinoma.

Vocal instabilities in a three-dimensional body-cover phonation model.

The goal of this study is to identify vocal fold conditions that produce irregular vocal fold vibration and the underlying physical mechanisms. Using a three-dimensional computational model of phonation, parametric simulations are performed with co-variations in vocal fold geometry, stiffness, and vocal tract shape. For each simulation, the cycle-to-cycle variations in the amplitude and period of the glottal area function are calculated, based on which the voice is classified into three types corresponding to regular, quasi-steady or subharmonic, and chaotic phonation. The results show that vocal folds with a large medial surface vertical thickness and low transverse stiffness are more likely to exhibit irregular vocal fold vibration when tightly approximated and subject to high subglottal pressure. Transition from regular vocal fold vibration to vocal instabilities is often accompanied by energy redistribution among the first few vocal fold eigenmodes, presumably due to nonlinear interaction between eigenmodes during vocal fold contact. The presence of a vocal tract may suppress such contact-related vocal instabilities, but also induce new instabilities, particularly for less constricted vocal fold conditions, almost doubling the number of vocal fold conditions producing irregular vibration.

Voice instabilities in a three-dimensional continuum model of phonation

The goal of this study is to identify vocal fold conditions that produce irregular vocal fold vibration and the underlying physical mechanisms. Using a three-dimensional computational model of phonation, parametric simulations are performed with co-variations in vocal fold geometry, stiffness, and vocal tract shape. For each simulation, the cycle-to-cycle variations in the amplitude and period of the glottal area function are calculated, based on which the voice are classified into three types corresponding to regular, quasi-steady or subharmomic, and chaotic phonation. The results show that the presence of a vocal tract significantly increases the occurrence of irregular vocal fold vibration, which naturally occurs even under symmetric vocal fold conditions, in particular for vocal folds with very low transverse stiffness in the coronal plane or a soft vocal fold body layer. The occurrence of voice instability is suppressed by increasing the transverse stiffness, increasing the body-cover ratio in the longitudinal stiffness, or decreasing the subglottal pressure. The implications of these observations on the production of certain voice qualities are discussed. [Work supported by NIH.]

On the necessity of using 3D imaging of vocal fold vibration

Physical mechanisms of regular and irregular vocal fold vibration were first studied using a computational model of vocal fold vibration. Later physical mechanisms of vocal fold vibration were studied in laboratory hemilarynx studies, where the medial surface of the vocal folds were imaged. While the method was also extended to clinical studies of vocal vibration, the method exhibited significantly less interpretive power in the clinical applications in which the superior surface of the vocal folds was imaged in 2D. Our hypothesis is that the interpretive power of the method of empirical eigenfunctions in studying the superior surface dynamics of the vocal folds will be significantly increased if one performs 3D imaging of the dynamics versus the standard 2D imaging. To test this hypothesis, the method of empirical eigenfunctions was employed on the same finite element model used in previous computational experiments. Our results confirm the hypothesis that the interpretive power of the method of empirical eigenfunctions was significantly increased in studying the superior surface dynamics of the vocal folds when 3D imaging was employed.

The shouted voice: A pilot study of laryngeal physiology under extreme aerodynamic pressure

Introduction: The objective was to study the behavior of the larynx during shouted voice production, when the larynx is exposed to extremely high subglottic pressure.Materials and methods: The study involved electroglottographic, acoustic, and aerodynamic analyses of shouts produced at maximum effort by three male participants.Results and discussion: Under a normal speaking voice, the voice sound pressure level (SPL) is proportional to the subglottic pressure. However, when the subglottic pressure reached high levels, the voice SPL reached a maximum value and then decreased as subglottic pressure increased further. Furthermore, the electroglottographic signal sometimes lost its periodicity during the shout, suggesting irregular vocal fold vibration.

Characterization of laryngealization as irregular vocal fold vibration and interaction with prosodic prominence

This paper introduces an original variant of recurrence analysis to quantify the degree of regularity of vocal fold vibration as captured by electroglottography during phonation. The proposed technique is applied to the analysis of laryngealized phonation as this phonation type typically shows irregular vibration cycles. The reliability of this approach is validated with synthetic vocal fold vibration signals, demonstrating that it permits measuring the regularity of vocal fold vibration, unaffected by changes in fundamental frequency. The method is also applied to real electroglottographic signals recorded at the onset of vowel-initial nonsense words produced in a speeded repetition task by five female German speakers. Results show that the degree of laryngealization during the production of word-initial vowels is modulated by the presence of stress (with stressed vowels being less laryngealized). Due to its robustness to changes of F0, the proposed technique proves to be a suitable tool for studying vocal fold regularity in concatenated speech. Its applications are not limited to the study of glottalization, since the degree of regularity of vocal fold vibration has paralinguistic functions and is a clinically relevant measure of voice pathologies.

Complex vibratory patterns in an elephant larynx

Elephants' low-frequency vocalizations are produced by flow-induced self-sustaining oscillations of laryngeal tissue. To date, little is known in detail about the vibratory phenomena in the elephant larynx. Here, we provide a first descriptive report of the complex oscillatory features found in the excised larynx of a 25 year old female African elephant (Loxodonta africana), the largest animal sound generator ever studied experimentally. Sound production was documented with high-speed video, acoustic measurements, air flow and sound pressure level recordings. The anatomy of the larynx was studied with computed tomography (CT) and dissections. Elephant CT vocal anatomy data were further compared with the anatomy of an adult human male. We observed numerous unusual phenomena, not typically reported in human vocal fold vibrations. Phase delays along both the inferior-superior and anterior-posterior (A-P) dimension were commonly observed, as well as transverse travelling wave patterns along the A-P dimension, previously not documented in the literature. Acoustic energy was mainly created during the instant of glottal opening. The vestibular folds, when adducted, participated in tissue vibration, effectively increasing the generated sound pressure level by 12 dB. The complexity of the observed phenomena is partly attributed to the distinct laryngeal anatomy of the elephant larynx, which is not simply a large-scale version of its human counterpart. Travelling waves may be facilitated by low fundamental frequencies and increased vocal fold tension. A travelling wave model is proposed, to account for three types of phenomena: A-P travelling waves, 'conventional' standing wave patterns, and irregular vocal fold vibration.

Arytenoid Adduction for Correcting Vocal Fold Asymmetry: High-Speed Imaging

We hypothesized that high-speed digital imaging provides a quantitative method to evaluate the effect of arytenoid adduction for the correction of asymmetric and irregular vocal fold vibration in unilateral vocal fold paralysis. Six subjects with unilateral vocal fold paralysis participated in the study (4 male, 2 female; mean [-SD] age, 52.5 +/- 21.3 years). Videokymographic and laryngotopographic methods for image analysis were performed for high-speed recordings of vocal fold vibration for visualizing the glottal vibratory patterns, and for quantifying the frequency of vibration of each vocal fold, respectively. Comparisons of the paralyzed and the normal vocal folds were made before and after arytenoid adduction. Analysis of the laryngotopographs revealed 2 distinct frequencies of vibration for the paralyzed and the contralateral vocal folds for all subjects before surgery. After arytenoid adduction, the vibration frequencies became identical or nearly identical in all subjects. Asymmetric vibration in vocal fold paralysis was exemplified by differences in vibration frequency between the vocal folds. The present data showed that after arytenoid adduction the vibration frequencies and the vibratory patterns of the contralateral vocal folds approached symmetry. This surgical procedure could improve the functional symmetry of the larynx for phonation.

Collagen Injection for Correcting Vocal Fold Asymmetry: High-Speed Imaging

We hypothesized that high-speed digital imaging with videokymographic and laryngotopographic analysis would provide a quantitative method to evaluate the effect of collagen injection for the correction of asymmetric and irregular vocal fold vibration in unilateral vocal fold paralysis. Videokymographic and laryngotopographic analysis was performed for high-speed digital recordings of vocal fold vibration for visualizing the glottal vibratory patterns, and for quantifying the frequency of vibration of each vocal fold, respectively, including comparisons between the paralyzed and normal vocal folds before and after surgery. This included prospective observations of 11 subjects with unilateral vocal fold paralysis (4 male, 7 female; mean +/- SD age, 67.1 +/- 12.0 years) using high-speed digital image analysis before and after collagen injection. Analysis of the laryngotopographs revealed 2 distinct frequencies of vibration for the paralyzed and contralateral vocal folds for 8 of the 11 subjects before surgery. After collagen injection, the vibration frequencies became identical, despite asymmetric vibration amplitudes. Asymmetric vibration amplitudes were also observed in the other 3 subjects before surgery, but the amplitudes became symmetric after collagen injection, despite a persistent phase shift. Asymmetric vibration in vocal fold paralysis was exemplified by differences in vibration frequency and amplitude between the vocal folds. The present study showed that after collagen injection, these aspects of vibratory patterns improved toward symmetry. This surgical procedure could improve the functional symmetry of the larynx for phonation.

Spatio-temporal quantification of vocal fold vibrations using high-speed videoendoscopy and a biomechanical model

Pathologic changes within the organic constitution of vocal folds or a functional impairment of the larynx may result in disturbed or even irregular vocal fold vibrations. The consequences are perturbations of the acoustic speech signal which are perceived as a hoarse voice. By means of appropriate image processing techniques, the vocal fold dynamics are extracted from digital high-speed videos. This study addresses the approach to obtain a parametric description of the spatio-temporal characteristics of the vocal fold oscillations for the aim of classification. For this purpose a biomechanical vocal fold model is introduced. An automatic optimization procedure is developed for fitting the model dynamics to the observed vocal fold oscillations. Thus, the resulting parameter values represent a specific vibration pattern and serve as an objective quantification measure. Performance and reliability of the optimization procedure are validated with synthetically generated data sets. The high-speed videos of two normal voice subjects and six patients suffering from different voice disorders are processed. The resulting model parameters represent a rough approximation of physiological parameters along the entire vocal folds.

Phonovibrogram Visualization of Entire Vocal Fold Dynamics

High-speed (HS) video recordings are the up-to-date method for visualizing irregular vocal fold vibrations. However, perceptive evaluation during offline replay is time consuming and shows high inter-rater variability. A visualization procedure is presented that extracts vocal fold vibrations from HS videos and transfers the motion information into a set of three phonovibrogram (PVG) images that make visual vocal fold displacements (PVG-0), velocities (PVG-1), and accelerations (PVG-2). The principles of PVG computation as well as their application to three clinical examples (normal voice, laryngeal nerve paralysis, functional voice disorder with vocal nodules) are presented. For normal and dysphonic subjects, the PVG images show the characteristics of vocal fold vibrations as concern the dynamic patterns of displacements, velocities, and accelerations. The PVG approach makes visual the entire range of motion of vibrating vocal fold edges in easy-to-read color images for differentiation of normal and pathologic voices. PVG images are printable and can be stored on a hard-disc drive, enabling the documentation of the course of voice disorders that is essential for evidenced-based medicine. PVG visualization has the potential to overcome the subjective quality of assessing HS videos, which makes it a valuable tool with broad clinical application.

Model-based quantification of pathological voice production

Hoarseness, the primary symptom of voice disorders, results from irregular vocal fold vibrations. The oncological therapy of laryngeal cancer may even result in a total loss of voice if an excision of the larynx, and thus, the vocal folds, is necessary. State-of-the-art voice rehabilitation technique in this case is the utilization of scarred tissue in the upper part of the esophagus for substitute voice production. The quality of laryngeal voice, as well as the substitute voice, primarily depends on the anatomy and the vibration patterns of the voice-producing element. Using endoscopic high-speed recordings, the voice generators are observed during voice production. In this work, a model-based approach feasible for the analysis and objective quantification of vocal fold vibrations, as well as the PE dynamics, is presented. By means of an automatic parameter optimization, the dynamic of a biomechanical model of the considered voice-producing element is fitted to the recorded vibration patterns. Thereby spatial and temporal properties of the vibrations are incorporated. The resulting values of the optimization parameters represent an objective quantification of the vibration patterns. In addition, the model parameters enable an approximation of physiological tissue parameters as stiffness and mass distribution.

Mechanisms of irregular vibration in a physical model of the vocal folds

Previous investigations have shown that one mechanism of irregular vocal fold vibration may be a desynchronization of two or more vibratory modes of the vocal fold tissues. In the current investigation, mechanisms of irregular vibration were further examined using a self-oscillating, physical model of vocal fold vibration, a hemi-model methodology, and high-speed, stereoscopic, digital imaging. Using the method of empirical eigen-functions, a spatiotemporal analysis revealed mechanisms of irregular vibration in subharmonic phonation and biphonation, which were not disclosed in a standard acoustic spectrum.

Classification of Unilateral Vocal Fold Paralysis by Endoscopic Digital High-Speed Recordings and Inversion of a Biomechanical Model

Hoarseness in unilateral vocal fold paralysis is mainly due to irregular vocal fold vibrations caused by asymmetries within the larynx physiology. By means of a digital high-speed camera vocal fold oscillations can be observed in real-time. It is possible to extract the irregular vocal fold oscillations from the high-speed recordings using appropriate image processing techniques. An inversion procedure is developed which adjusts the parameters of a biomechanical model of the vocal folds to reproduce the irregular vocal fold oscillations. Within the inversion procedure a first parameter approximation is achieved through a knowledge-based algorithm. The final parameter optimization is performed using a genetic algorithm. The performance of the inversion procedure is evaluated using 430 synthetically generated data sets. The evaluation results comprise an error estimation of the inversion procedure and show the reliability of the algorithm. The inversion procedure is applied to 15 healthy voice subjects and 15 subjects suffering from unilateral vocal fold paralysis. The optimized parameter sets allow a classification of pathologic and healthy vocal fold oscillations. The classification may serve as a basis for therapy selection and quantification of therapy outcome in case of unilateral vocal fold paralysis.

Objective vocal fold vibration assessment from videokymographic images

Vocal folds oscillation crucially influences all the basic qualities of voice, such as pitch and loudness, as well as the spectrum. Stroboscopy provides the standard view of the larynx. However, a two-dimensional high-speed imaging system currently cannot provide enough image resolution to evaluate irregular vocal fold vibrations, due to the limitation of transmission speed and storage volume. Videokymography is a new diagnostic tool developed to overcome specific limitations of stroboscopy in severely dysphonic patients with an aperiodic signal. It registers the movements of the vocal folds with a high time resolution on a line perpendicular to the glottis. The technique, being independent from the periodicity and intensity of the vocal signal, allows an objective evaluation of vocal folds function. However, due to its novelty, no established clinical evaluation protocol, or validity and reliability data are available for videokymography. Moreover, few results concerning objective parameter estimation from videokymographic images are available. The main focus of this paper is on measuring and tracking quantitative parameters for objective vocal fold functional assessment, from videokymographic (VKG) examinations of subjects with normal and pathological laryngeal function, based on active contour search implemented with a properly adjusted robust snake algorithm. The method is designed to deliver to the clinician the essential objective information of VKG in an effective way, as an aid to its subjective and intuitive skilfulness. A set of VKG images has been analysed, coming both from healthy and dysphonic subjects, recorded at the Otolaryngology Department, University of Milan, Italy, showing the robustness and reliability of the proposed technique.