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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.

Introduction Identifying the mucosal wave (MW) is essential when studying the voice; however, its characterization and perceived measurement during laryngeal stroboscopy (LS) are not well defined or standardized because of the subjectivity of its interpretation. This article proposed and validated a scale that characterized and approximated MW measurement during LS, applied it to participants divided into a healthy group and groups with free edge conditions, and identified differences between them. Methods This is a descriptive and clinical validation study of the “VASQ (Vertical axis, Anteroposterior axis, Symmetry and Quantity) mucosal wave score” scale based on stroboscopy images of 137 adult men and women divided into a control group and functional and organic pathology groups. The images were analyzed by three evaluators according to an established protocol. Measurements dictating the reproducibility and validity criteria as well as the MW score in each group were obtained. Results The reliability of the scale was α = 0.90, internal consistency success rate was 91%, intra-observer reliability was 0.83, inter-observer reliability was 0.83, content validity coefficient was 0.92, and factor loading was 0.37–0.53. The MW total score values between 5 and 6 were established as a reference for normality (P < 0.05). Organic pathology showed lower MW score values (P < 0.05), and functional pathology to a lesser extent (P > 0.05). Conclusions The proposed scale is a consistent, valid, and reliable tool. Its widespread application would favor commonly used terminology and facilitate quantitative comparisons in future studies.

This study examines the impact of vocal fold (VF) lesions located on the superior surface on glottal airflow dynamics and tissue oscillatory behaviors using biomechanical simulations of a two-layered realistic VF model. It is hypothesized that morphological changes in the VFs due to the presence of a lesion cause changes in tissue elasticity and rheological properties, contributing to dysphonia. Previous research has lacked the integration of lesions in computational simulations of anatomically accurate larynx-VF models to explore their effects on phonation and contribution to voice disorders. Addressing the current gap in literature, this paper considers a computational model of a two-layered VF structure incorporating a lesion that represents a hemorrhagic polyp. A three-dimensional, subject-specific, multilayered geometry of VFs is constructed based on STL files derived from a human larynx CT scan, and a fluid–structure interaction (FSI) methodology is employed to simulate the coupling of glottal airflow and VF tissue dynamics. To evaluate the effects of the lesion’s presence, two FSI models, one with a lesion embedded in the cover layer and one without, are simulated and compared. Analysis of airflow dynamics and tissue vibrational patterns between these two models is used to determine the impact of the lesion on the biomechanical characteristics of phonation. The polyp is found to slightly increase airflow resistance through the glottis and disrupt vibratory symmetry by decreasing the vibration frequency of the affected fold, leading to weaker and less rhythmic oscillations. The results also indicate that the lesion increases tissue stress in the affected fold, which agrees with clinical observations. While quantitative ranges depend on lesion size and tissue properties, these consistent and physically meaningful trends highlight the biomechanical mechanisms by which lesions influence phonation.

The influence of asymmetric vocal fold stiffness on voice production was evaluated using life-sized, self-oscillating vocal fold models with an idealized geometry based on the human vocal folds. The models were fabricated using flexible, materially-linear silicone compounds with Young's modulus values comparable to that of vocal fold tissue. The models included a two-layer design to simulate the vocal fold layered structure. The respective Young's moduli of elasticity of the “left” and “right” vocal fold models were varied to create asymmetric conditions. High-speed videokymography was used to measure maximum vocal fold excursion, vibration frequency, and left–right phase shift, all of which were significantly influenced by asymmetry. Onset pressure, a measure of vocal effort, increased with asymmetry. Particle image velocimetry (PIV) analysis showed significantly greater skewing of the glottal jet in the direction of the stiffer vocal fold model. Potential applications to various clinical conditions are mentioned, and suggestions for future related studies are presented.

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.

Mechanotransduction is a crucial property in all organisms, modulating cellular behaviors in response to external mechanical stimuli. Given the high mobility of vocal folds, it is hypothesized that mechanotransduction significantly contributes to their tissue homeostasis. Recent studies have identified mechanosensitive proteins in vocal fold epithelia, supporting this hypothesis. Voice therapy, which, involves the mobilization of vocal folds, aims to rehabilitate vocal function and restore homeostasis. However, establishing a direct causal link between specific mechanical stimuli and therapeutic benefits is challenging due to the variability in voice therapy techniques. This challenge is further compounded when investigating biological benefits in humans. Vocal fold tissue cannot be biopsied without significant impairment of the vibratory characteristics of the vocal folds. Conversely, studies using vocal fold mimetic bioreactors have demonstrated that mechanical stimulation of vocal fold fibroblasts can lead to highly heterogeneous responses, depending on the nature and parameters of the induced vibration. These responses can either aid or impede vocal fold vibration at the physiological level. Future research is needed to determine the specific mechanical parameters that are biologically beneficial for vocal fold function.

Although many quantitative parameters have been devised to describe abnormalities in vocal fold vibration, little is known about the priority of these parameters. We conducted a prospective study using high-speed digital imaging to elucidate disease-specific key parameters (KPs) to characterize the vocal fold vibrations of individual voice disorders. From 304 patients with various voice disorders and 46 normal speakers, high-speed digital imaging of a sustained phonation at a comfortable pitch and loudness was recorded and parameters from visual-perceptual rating, laryngotopography, digital kymography, and glottal area waveform were calculated. Multivariate analysis was then applied to these parameters to elucidate the KPs to explain each voice disorder in comparison to normal subjects. Four key parameters were statistically significant for all laryngeal diseases. However, the coefficient of determination (R2) was very low (0.29). Vocal fold paralysis (8 KPs, R2 = 0.76), sulcus vocalis (4 KPs, R2 = 0.74), vocal fold scarring (1 KP, R2 = 0.68), vocal fold atrophy (6 KPs, R2 = 0.53), and laryngeal cancer (1 KP, R2 = 0.52) showed moderate-to-high R2 values. The results identified different KPs for each voice disorder; thus, disease-specific analysis is a reasonable approach.

High-speed videoendoscopy (HSV) captures the true intracycle vibratory behavior of the vocal folds, which allows for overcoming the limitations of videostroboscopy for more accurate objective quantification methods. However, the commercial HSV systems have not gained widespread clinical adoption because of remaining technical and methodological limitations and an associated lack of information regarding the validity, practicality, and clinical relevance of HSV. The purpose of this article is to summarize the practical, technological and methodological challenges we have faced, to delineate the advances we have made, and to share our current vision of the necessary steps towards developing HSV into a robust tool. This tool will provide further insights into the biomechanics of laryngeal sound production, as well as enable more accurate functional assessment of the pathophysiology of voice disorders leading to refinements in the diagnosis and management of vocal fold pathology. The original contributions of this paper are the descriptions of our color high-resolution HSV integration, the methods for facilitative playback and HSV dynamic segmentation, and the ongoing efforts for implementing HSV in phonomicrosurgery, as well as the analysis of the challenges and prospects for the clinical implementation of HSV, additionally supported by references to previously reported data.

A full three-dimensional (3D) fluid-structure interaction (FSI) study of subject-specific vocal fold vibration is carried out based on the previously reconstructed vocal fold models of rabbit larynges. Our primary focuses are the vibration characteristics of the vocal fold, the unsteady 3D flow field, and comparison with a recently developed 1D glottal flow model that incorporates machine learning. The 3D FSI model applies strong coupling between the finite-element model for the vocal fold tissue and the incompressible Navier-Stokes equation for the flow. Five different samples of the rabbit larynx, reconstructed from the magnetic resonance imaging (MRI) scans after the in vivo phonation experiments, are used in the FSI simulation. These samples have distinct geometries and a different inlet pressure measured in the experiment. Furthermore, the material properties of the vocal fold tissue were determined previously for each individual sample. The results demonstrate that the vibration and the intraglottal pressure from the 3D flow simulation agree well with those from the 1D flow model based simulation. Further 3D analyses show that the inferior and supraglottal geometries play significant roles in the FSI process. Similarity of the flow pattern with the human vocal fold is discussed. This study supports the effective usage of rabbit larynges to understand human phonation and will help guide our future computational studies that address vocal fold disorders.

Objectives: Kymographic imaging through videokymography has been recognized as a convenient, novel way to display laryngeal behavior, yet little systematic research has been done to map the relevant features displayed in such images. Here we have aimed at specification of these features to enable systematic visual characterization and categorization of vocal fold vibratory patterns in voice disorders. Methods: A cross-sectional, descriptive design was used. We selected 45 subjects and extracted 100 videokymographic images from the archive of more than 7,000 videokymographic examinations of subjects with a wide range of voice disorders. The images showed a large variety of vocal fold vibratory behaviors during sustained phonations. We visually identified the prominent features that distinguished the vibration patterns across the images. Results: We divided the findings into 10 feature categories. They included refined traditional features (eg, mucosal waves), as well as additional features that are obscured in strobolaryngoscopy (eg, different types of irregularities, left-right frequency differences, shapes of lateral and medial peaks, cycle aberrations). Conclusions: The variations in the identified features reveal different behavioral origins of voice disorders. The findings open new possibilities for objective documentation and for monitoring vocal fold behavior in clinical practice through kymographic imaging.