Damping of vocal fold oscillation at voice offset

Bioreactors for Vocal Fold Tissue Engineering

It is estimated that almost one-third of the United States population will be affected by a vocal fold (VF) disorder during their lifespan. Promising therapies to treat VF injury and scarring are mostly centered on VF tissue engineering strategies such as the injection of engineered biomaterials and cell therapy. VF tissue engineering, however, is a challenging field as the biomechanical properties, structure, and composition of the VF tissue change upon exposure to mechanical stimulation. As a result, the development of long-term VF treatment strategies relies on the characterization of engineered tissues under a controlled mechanical environment. In this review, we highlight the importance of bioreactors as a powerful tool for VF tissue engineering with a focus on the current state of the art of bioreactors designed to mimic phonation in vitro. We discuss the influence of the phonatory environment on the development, function, injury, and healing of the VF tissue and its importance for the development of efficient therapeutic strategies. A concise and comprehensive overview of bioreactor designs, principles, operating parameters, and scalability are presented. An in-depth analysis of VF bioreactor data to date reveals that mechanical stimulation significantly influences cell viability and the expression of proinflammatory and profibrotic genes in vitro. Although the precision and accuracy of bioreactors contribute to generating reliable results, diverse gene expression profiles across the literature suggest that future efforts should focus on the standardization of bioreactor parameters to enable direct comparisons between studies. Impact statement We present a comprehensive review of bioreactors for vocal fold (VF) tissue engineering with a focus on the influence of the phonatory environment on the development, function, injury, and healing of the VFs and the importance of mimicking phonation on engineered VF tissues in vitro. Furthermore, we put forward a strong argument for the continued development of bioreactors in this area with an emphasis on the standardization of bioreactor designs, principles, operating parameters, and oscillatory regimes to enable comparisons between studies.

Vocal Release Time of Mandarin Vowels at Different Pitch Levels

OBJECTIVE

To explore how vocal release time (VRT) varies when young adults articulate the three Chinese vertex vowels with increasingly higher pitch levels.

STUDY DESIGN

Sound pressure (SP) and electroglottographic (EGG) signals were recorded synchronously from 53 males and 53 females saying sustained /A/, /i/, /u/ at five equally spaced pitch heights, each being higher than the one before.

METHODS

About 3030 effective ST (semitone) and VRT measures were obtained. Statistical analyses of them were done by using SPSS 13.0 and Excel 2010.

FINDINGS

As mean STs increase linearly from pitch levels one to five, mean VRTs display a rise-fall pattern in a big group of subjects, but a fall-rise pattern in a small group of them. In both cases, pitch and VRT tend to present a curvilinear relationship, although VRT varies in opposite directions. And also, high vowels tend to have larger VRT than low vowels.

Intraglottal Aerodynamics at Vocal Fold Vibration Onset

The most frequently observed type of voice onset in spontaneous speech in normal subjects is the soft onset, and it may be considered as the "physiological" onset. It starts from an immobile narrow glottal slit crossed by a continuous airflow, and then a few oscillations (even a single one in some cases) precede the first glottal closure. It is a transient event, during which the acting forces, lung pressure, intraglottal pressure, myoelastic tension of the vocal fold (VF) oscillator and inertance of the supraglottal vocal tract, interact to progressively reach the steady state of a sustained oscillation. Combined measurements of flow, area, and pressure provide a detailed qualitative and quantitative analysis of the intraglottal mechanical events at the precise moment of starting oscillation in a physiological (soft or soft/breathy) onset. Our in vivo measurements of airflow and glottal area show that the very first oscillation occurs exactly at the time when turbulence appears at the level of the glottal narrowing, ie, when the Reynolds number reaches its critical value. The turbulence may be assumed to trigger an oscillator consisting in the ensemble of the VFs and the air of the vocal tract, which is known to be weakly damped. Turbulence can act here as an aspecific flick, triggering the oscillator, the frequency of oscillation being determined by its mechanical properties. Furthermore, the first noticeable glottal oscillations are sinusoidal: the VFs are neither steeply sucked together by a negative Bernoulli pressure, nor burst apart by the lung pressure. Our measurements show that, at the critical time, the rising positive lung pressure is balanced by the rising negative Bernoulli pressure generated by the transglottal flow.

In Vivo Quantification of the Intraglottal Pressure: Modal Phonation and Voice Onset

Intraglottal pressure is the driving force of vocal fold vibration. Its time course during the open phase of the vibratory cycle is essential in the mechanics of phonation, but measuring it directly is difficult and may hinder spontaneous voicing. However, it can be computed from the in vivo measured transglottal flow and glottal area (hence the air particle velocity) on the basis of the Bernoulli energy law and the interaction with the inertance of the vocal tract. As to sustained modal phonation, calculations are presented for the two possible shapes of glottal duct: convergent and divergent, including absolute calibration in order to obtain quantitative physical values. Whatever the glottal duct configuration, the calculations based on measured values of glottal area and air flow show that the integrated intraglottal pressure during the opening phase systematically exceeds that during the closing phase, which is the basic condition for sustaining vocal fold oscillation. The key point is that the airflow curve is skewed to the right relative to the glottal area curve. The skewing results from air compressibility and vocal tract inertance. The intraglottal pressure becomes negative during the closing phase. As to the soft (or physiological) voice onset, a similar approach shows that the integrated pressure differences (opening phase - closing phase) actually increase as the onset progresses, and this applies to the results based on Bernoulli's energy law as well as to those based on the interaction with the inertance of the vocal tract. Furthermore and similarly, the phase lead of the pressure wave with respect to the glottal opening progressively increases. The underlying explanation lies in the progressively increasing skewing of the airflow curve to the right with respect to the glottal area curve.