Artificial Vocal Folds Research Articles

Analysis of a Soft Bio-Inspired Active Actuation Model for the Design of Artificial Vocal Folds

AbstractPhonation results from the passively induced oscillation of the vocal folds in the larynx, creating sound waves that are then articulated by the mouth and nose. Patients undergoing laryngectomy have their vocal folds removed and thus must rely on alternative sources of achieving the desired vibration of artificial vocal folds. Existing solutions, such as voice prostheses and the Electrolarynx, are limited by producing sufficient voice quality, for instance. In this paper, we present a mathematical analysis of a physical model of an active vocal fold prosthesis. The inverse dynamical equation of the system will help to understand whether specific types of soft actuators can produce the required force to generate natural phonations. Hence, this is referred to as the active actuation model. We present the analysis to replicate the vowels /a/, /e/, /i/, and /u/ and voice qualities of vocal fry, modal, falsetto, breathy, pressed, and whispery. These characteristics would be required as a first step to design an artificial vocal folds system. Inverse dynamics is used to identify the required forces to change the glottis area and frequencies to achieve sufficient oscillation of artificial vocal folds. Two types of ionic polymer-metal composite (IPMC) actuators are used to assess their ability to produce these forces and the corresponding activation voltages required. The results of our proposed analysis will enable research into the effects of natural phonation and, further, provide the foundational work for the creation of advanced larynx prostheses.

A Deep Learning Enhanced Novel Software Tool for Laryngeal Dynamics Analysis.

Purpose High-speed videoendoscopy (HSV) is an emerging, but barely used, endoscopy technique in the clinic to assess and diagnose voice disorders because of the lack of dedicated software to analyze the data. HSV allows to quantify the vocal fold oscillations by segmenting the glottal area. This challenging task has been tackled by various studies; however, the proposed approaches are mostly limited and not suitable for daily clinical routine. Method We developed a user-friendly software in C# that allows the editing, motion correction, segmentation, and quantitative analysis of HSV data. We further provide pretrained deep neural networks for fully automatic glottis segmentation. Results We freely provide our software Glottis Analysis Tools (GAT). Using GAT, we provide a general threshold-based region growing platform that enables the user to analyze data from various sources, such as in vivo recordings, ex vivo recordings, and high-speed footage of artificial vocal folds. Additionally, especially for in vivo recordings, we provide three robust neural networks at various speed and quality settings to allow a fully automatic glottis segmentation needed for application by untrained personnel. GAT further evaluates video and audio data in parallel and is able to extract various features from the video data, among others the glottal area waveform, that is, the changing glottal area over time. In total, GAT provides 79 unique quantitative analysis parameters for video- and audio-based signals. Many of these parameters have already been shown to reflect voice disorders, highlighting the clinical importance and usefulness of the GAT software. Conclusion GAT is a unique tool to process HSV and audio data to determine quantitative, clinically relevant parameters for research, diagnosis, and treatment of laryngeal disorders. Supplemental Material https://doi.org/10.23641/asha.14575533.

Airflow driven fluid–structure interaction subjected to aqueous-based liquid spraying

Artificial saliva sprays are commonly used to remedy vocal folds surface hydration. Vocal folds surface hydration and its effect on their auto-oscillation are studied experimentally using artificial vocal folds. The airflow is used to excite the vocal folds into auto-oscillation after which the vocal folds surface is sprayed with a liquid. The validity of the findings described in a previous study [A. Bouvet, X. Pelorson, and A. Van Hirtum, “Influence of water spraying on an oscillating channel,” J. Fluids Struct. 93, 102840 (2020)] concerning the effect of water spraying is further investigated. First, artificial saliva sprays (up to 5 ml) are sprayed instead of water. It is shown that this allows us to address the effect of increased dynamic viscosity (up to 8 times compared to water) as other artificial saliva properties affecting air–liquid mixing and surface wettability remain similar to water. Second, the Reynolds number in the dry stage is systematically increased (with 60%) for constant spraying volume ≥3 ml. Regardless of the sprayed liquid and Reynolds number, oscillation cycles are characterized by an increase in mean upstream pressure, cycle-to-cycle variability, and a decrease in oscillation frequency due period doubling. Increasing the dynamic viscosity tends to reduce the magnitude of these tendencies for spraying volumes smaller than 3 ml, indicating that viscous liquid–gas mixing affects the flow regime. Systematic Reynolds number variation shows that liquid spraying increases the oscillation onset threshold pressure and that the magnitude of general tendencies is reduced. The assessed conditions and features are pertinent to human voice production after hydration with an artificial saliva spray burst.

Sound-producing voice prostheses: 150 years of research.

Advanced laryngeal cancer sometimes necessitates the removal of the complete larynx. This procedure involves suturing the trachea to an opening in the neck, the most disturbing consequence of which is the loss of voice. Since 1859, several devices have been developed for voice restoration, based mainly on a vibrating reed element. However, the resulting sound is very monotonous and thus unpleasant. Presently the most successful way of voice restoration is the placement of a one-way shunt valve in the tracheo-esophageal wall, thus preventing aspiration and allowing air to flow from the lungs to the esophagus, where soft tissues start to vibrate for substitute voicing. However, the quality of this voice is often poor. New artificial vocal folds to be placed within the shunt valve have been developed, and a membrane-principle concept appears very promising, owing to the self-cleaning construction and the high voice quality. Future developments will include electronic voice sources. Hopefully these developments will result in a high-quality voice, after 150 years of research.

Development of a small film sensor for the estimation of the contact pressure of artificial vocal folds

Since voice production is the precondition for speech and, therefore, verbal communication, people suffering from voice disorders are limited in their everyday life. Physiological voice disorders, like vocal fold nodules are understood to result from increased contact pressure of the vocal folds during vibration. Thus, measurement of arising contact pressure during vocal fold oscillation helps quantify the collision forces and to substantiate previous assumptions. Due to limited access to the vocal folds, there is need for a small sensor that minimally influences air flow. For that purpose, we developed a small film sensor which is capable of measuring the contact pressure along the vocal fold contact areas. To investigate the suitability of the sensor, a hemi-larynx flow channel experiment with silicone replicas of the vocal folds was performed. Replicas of different elasticities were investigated. The contact sensor signals as well as the subglottal pressure were acquired. High-speed recordings of the vocal fold oscillation were synchronously performed to accurately relate the opening, closing and contact phases to the time signals. The measured contact pressures will be reported and compared to previous results. The advantages and limitations of the developed sensor will be discussed.

In Vitro Experimental Investigation of Voice Production

The process of human phonation involves a complex interaction between the physical domains of structural dynamics, fluid flow, and acoustic sound production and radiation. Given the high degree of nonlinearity of these processes, even small anatomical or physiological disturbances can significantly affect the voice signal. In the worst cases, patients can lose their voice and hence the normal mode of speech communication. To improve medical therapies and surgical techniques it is very important to understand better the physics of the human phonation process. Due to the limited experimental access to the human larynx, alternative strategies, including artificial vocal folds, have been developed. The following review gives an overview of experimental investigations of artificial vocal folds within the last 30 years. The models are sorted into three groups: static models, externally driven models, and self-oscillating models. The focus is on the different models of the human vocal folds and on the ways in which they have been applied.

Simulation based estimation of dynamic mechanical properties for viscoelastic materials used for vocal fold models

In order to obtain a deeper understanding of the human phonation process and the mechanisms generating sound, realistic setups are built up containing artificial vocal folds. Usually, these vocal folds consist of viscoelastic materials (e.g., polyurethane mixtures). Reliable simulation based studies on the setups require the mechanical properties of the utilized viscoelastic materials. The aim of this work is the identification of mechanical material parameters (Young's modulus, Poisson's ratio, and loss factor) for those materials. Therefore, we suggest a low-cost measurement setup, the so-called vibration transmission analyzer (VTA) enabling to analyze the transfer behavior of viscoelastic materials for propagating mechanical waves. With the aid of a mathematical Inverse Method, the material parameters are adjusted in a convenient way so that the simulation results coincide with the measurement results for the transfer behavior. Contrary to other works, we determine frequency dependent functions for the mechanical properties characterizing the viscoelastic material in the frequency range of human speech (100–250 Hz). The results for three different materials clearly show that the Poisson's ratio is close to 0.5 and that the Young's modulus increases with higher frequencies. For a frequency of 400 Hz, the Young's modulus of the investigated viscoelastic materials is approximately 80% higher than for the static case (0 Hz). We verify the identified mechanical properties with experiments on fabricated vocal fold models. Thereby, only small deviations between measurements and simulations occur.

Mechanism of and threshold biomechanical conditions for falsetto voice onset.

The sound source of a voice is produced by the self-excited oscillation of the vocal folds. In modal voice production, a drastic increase in transglottal pressure after vocal fold closure works as a driving force that develops self-excitation. Another type of vocal fold oscillation with less pronounced glottal closure observed in falsetto voice production has been accounted for by the mucosal wave theory. The classical theory assumes a quasi-steady flow, and the expected driving force onto the vocal folds under wavelike motion is derived from the Bernoulli effect. However, wavelike motion is not always observed during falsetto voice production. More importantly, the application of the quasi-steady assumption to a falsetto voice with a fundamental frequency of several hundred hertz is unsupported by experiments. These considerations suggested that the mechanism of falsetto voice onset may be essentially different from that explained by the mucosal wave theory. In this paper, an alternative mechanism is submitted that explains how self-excitation reminiscent of the falsetto voice could be produced independent of the glottal closure and wavelike motion. This new explanation is derived through analytical procedures by employing only general unsteady equations of motion for flow and solids. The analysis demonstrated that a convective acceleration of a flow induced by rapid wall movement functions as a negative damping force, leading to the self-excitation of the vocal folds. The critical subglottal pressure and volume flow are expressed as functions of vocal fold biomechanical properties, geometry, and voice fundamental frequency. The analytically derived conditions are qualitatively and quantitatively reasonable in view of reported measurement data of the thresholds required for falsetto voice onset. Understanding of the voice onset mechanism and the explicit mathematical descriptions of thresholds would be beneficial for the diagnosis and treatment of voice diseases and the development of artificial vocal folds.

Optical Reconstruction of High-Speed Surface Dynamics in an Uncontrollable Environment

The ability to communicate with our voice can be regarded as the concatenation of the two processes "phonation" and "modulation." These take place in the larynx and palatal and oral region, respectively. During phonation the audible primary voice signal is created by mutual reaction of vocal folds with the exhaled air stream of the lungs. The underlying interactions of masses, fluids and acoustics have yet to be identified and understood. One part of the primary signal's acoustical source are vortex induced vibrations, as e.g., created by the Coandăeffect in the air stream. The development of these vorteces is determined by the shape and 3-D movements of the vocal folds in the larynx. Current clinical in vivo research methods for vocal folds do not deliver data of satisfactory quality for fundamental research, e.g., an endoscope is limited to 2-D image information. Based hereupon, a few improved methods have been presented, however delivering only selective 3-D information, either for a single point or a line. This stands in contrast to the 3-D motions of the entire vocal fold surface. More complex imaging methods, such as MRI, do not deliver information in real-time. Thus, it is necessary to develop an easily applicable, more improved examination method, which allows for 3-D data of the vocal folds surfaces to be obtained. We present a method to calibrate a 3-D reconstruction setup including a laser projection system and a high-speed camera. The setup is designed with miniaturization and an in vivo application in mind. The laser projection system generates a divergent grid of 196 laser dots by diffraction gratings. It is calibrated with a planar calibration target through planar homography. In general, the setup allows to reconstruct the topology of a surface at high frame rates (up to 4000 frames per second) and in uncontrollable environments, as e.g., given by the lighting situation (little to no ambient light) and varying texture (e.g., varying grade of reflection) in the human larynx. In particular, this system measures the 3-D vocal fold surface dynamics during phonation. Applied to synthetic data, the calibration is shown to be robust (error approximately 0.5 μm) regarding noise and systematic errors. Experimental data gained with a linear z -stage proved that the system reconstructs the 3-D coordinates of points with an error at approximately 15 μm. The method was applied exemplarily to reconstruct porcine and artificial vocal folds' surfaces during phonation. Local differences such as asymmetry between left and right fold dynamics, as well as global parameters, such as opening and closing speed and maximum displacements, were identified and quantified.

Experimental Analysis of the Characteristics of Artificial Vocal Folds

Specialized literature presents a number of models describing the function of the vocal folds. In most of those models, an emphasis is placed on the air flowing through the glottis and, further, on the effect of the parameters of the air alone (its mass, speed, and so forth). The article focuses on the constructional definition of artificial vocal folds and their experimental analysis. The analysis is conducted for voiced source voice phonation and for the changing mean value of the subglottal pressure. The article further deals with the analysis of the pressure of the airflow through the vocal folds, which is cut (separated) into individual pulses by the vibrating vocal folds. The analysis results show that air pulse characteristics are relevant to voice generation, as they are produced by the flowing air and vibrating vocal folds. A number of artificial vocal folds have been constructed to date, and the aforementioned view of their phonation is confirmed by their analysis. The experiments have confirmed that man is able to consciously affect only two parameters of the source voice, that is, its fundamental frequency and voice intensity. The main forces acting on the vocal folds during phonation are as follows: subglottal air pressure and elastic and inertia forces of the vocal folds' structure. The correctness of the function of the artificial vocal folds is documented by the experimental verification of the spectra of several types of artificial vocal folds.

Artificial vocal folds adjustments to a patient’s voice as easily as changing hearing aids or eyeglasses

For anti-ageing, devices and procedures to improve hearing (hearing aids, cochlear implants, etc.) and vision (eyeglass, intra ocular lens, etc.) are well established as communication support tools for the "speech chain". They can be fit to a person's individual needs, and adjusted as these needs change. However effective tools to improve voice problems associated with physiological aging are not so well established. Review previous phono surgical techniques with my experience, I propose a complete different approach for glottal incompetence. I suggest a new adjustable surgical technique as a replacement for previous injection techniques used to treat glottal incompetence. My proposed solution is to implant an inflatable bag, or balloon, on the lateral side of the vocal fold. Unlike Autologous transplantation of fascia into the vocal folds procedures, where the implanted material appears to become vocal-fold tissue, the new implant would function as an artificial vocal fold. Using the proposed technique, the degree of augmentation can be adjusted to meet changing physical conditions.

Eureka-project: 'totally implantable artificial larynx': progress report

The consequences of a laryngectomy and additional rehabilitation using a shunt valve and tracheostoma valve are still distressing. The European project 'Artificial larynx' aims at realization of ail implantable artificial larynx to eliminate the main drawbacks of the present rehabilitation. The artificial larynx will be made of biofilm-resistant material and consist of: artificial vocal folds with adjustable fundamental frequency and with variable frequency during speech to avoid monotony; an artificial epiglottis controlled by remnants of muscles or by pressure; a valve mechanism to switch between breathing and speaking; a tissue connector to connect the artificial larynx to the trachea. The valve mechanism has been developed and is now tested as tracheostoma valve. All other parts as well as surface modifications are in development.