Irregular Vocal Fold Vibration Research Articles

An asymmetric smooth contour two-mass model for recurrent laryngeal nerve paralysis

Irregular vocal fold vibrations are assumed to be a major cause of hoarseness. A common clinical condition presenting with hoarseness is a unilateral recurrent laryngeal nerve paralysis (RLNP). In order to explain high-speed video recordings of clinical RLNP, RLNP-type vocal fold vibrations are simulated by extending the well known two-mass model (2MM) to an asymmetric smooth-contour two-mass model (SC2MM). Polynomial interpolations form a smooth surface over the lumped elements of the 2MM. Laryngeal asymmetry is accounted for by introduction of an asymmetry coefficient and an anterior commissure angle which models a variable glottal closure insufficiency. Compared to the 2MM, the SC2MM yields a smaller glottal volume flow and is more stable in critical parameter constellations of RLNP-like conditions. It is able to model the vocal fold dynamics during a glottal closure insufficiency.

Analysis of modal and creaky voice quality variations

Voice quality, as a major vehicle of information about physical, phonological, and social characteristics of the speaker, has a vital semiotic role to play in spoken interaction [Laver (1968), Laver and Trudgill (1979)]. In the past couple of years, our lab developed an Aperiodicity/Periodicity/Pitch (APP) detector that produces a spectro-temporal profile of the periodic and aperiodic regions of the speech waveform [Deshmukh et al. (in press)]. To do so, the speech signal is passed through a 60-channel gamma tone auditory filterbank. The distribution of the dips occurring in the average magnitude difference function (AMDF) computed from each channel envelope is analyzed to determine periodicity and aperiodicity. Presently, the APP detector classifies both turbulent noise and irregular vocal fold vibration (creakiness) as aperiodic. In this work, we are investigating the detailed characteristics of the AMDF waveform when speech is creaky. This information is presently being used to distinguish aperiodicity due to turbulence from aperiodicity due to creakiness. We will present results from the refined APP detector using various male and female utterances from the TIMIT database.

What have we learned about laryngeal physiology from high-speed digital videoendoscopy?

The purpose of this review is to describe recent developments in high-speed videoendoscopy. The applications of this technique are highlighted and important findings regarding vocal fold physiology and voice pathology are discussed. The number of applications for digital high-speed imaging has increased during recent years because of the development of camera image sensor systems with increased image resolution of video and television quality. Other improvements are related to computer processing speed and storage capacity and the development of automatic algorithms for quantification and measurements both in time and room dimensions. This is enhanced by combining high-speed videoendoscopy with laser-based measurement systems, acoustic analyses or other glottographic methods, such as flow glottography or electroglottography. High-speed videoendoscopy is currently used in studies of voice mechanisms of phonation (e.g., the voice source can be examined with a high sampling rate, from 1000 to over 8000 frames per second), and in phonation onset or offset. High-speed imaging is also useful in linguistic studies and in the examination of different artistic singing styles, such as extremely high-pitched singing, throat singing, or different pop and rock styles. High-speed videoendoscopy is also used in the examination of patients with voice disorders, particularly with irregular vocal fold vibrations, ventricular phonation, or the phonation of individuals who have had a laryngectomy. Findings from studies of normal voice physiology and of voice disorders using high-speed imaging are presented and their relevance is discussed.

Videostrobokymographic Analysis of Benign Vocal Fold Lesions

Objectives—Videostrobokymography (VSK) has recently been introduced. The aim of this study was to analyze vibratory patterns and objective parameters in various benign vocal fold lesions using VSK and to examine the efficacy of VSK in clinical applications.Material and Methods—Using VSK, we analyzed the vibration patterns of normal vocal folds, various benign lesions such as nodules, polyps, cysts and Reinke's edema and cases of unilateral vocal fold paralysis. We also calculated the objective parameters open quotient and asymmetric index and compared them with their mean values in normal controls.Results—In nodules, polyps and cysts, the open quotient at the site of the lesion was similar to the mean value in the normal controls; however, on the other parts of the vocal folds, it was much larger than the normal mean value. In Reinke's edema, irregular and asymmetric vibrations were observed. The posterior area of the vocal folds showed larger open quotients than the anterior area. In unilateral vocal fold paralysis, irregular vocal fold vibration and incomplete closure of the vocal folds were documented. Much larger asymmetric indices were calculated for unilateral vocal fold paralysis than in normal controls or for other lesions. The asymmetric index may be a good quantitative parameter of vibration in patients with vocal fold paralysis.Conclusion—This study demonstrated that VSK could generate clear quantitative documentation of fine vibrations of vocal folds in many different types of benign lesion. VSK has the potential to be an effective tool for the quantitative analysis of vibratory patterns of vocal folds in clinical settings.

Chaotic vibration induced by turbulent noise in a two-mass model of vocal folds.

The contribution of turbulent noise was modeled in symmetric vocal folds. A two-mass model was used to simulate irregular vocal fold vibrations. The threshold values of system parameters to produce irregular vibrations were decreased as a result of turbulent airflow. Periodic vibrations were then driven into the regions of irregular vibrations. Using nonlinear dynamics including Poincaré map and Lyapunov exponents, irregular vibrations were demonstrated as chaos. For the deterministic vocal-fold model with noise free and steady airflow, a fine period-doubling bifurcation cascade was shown in a bifurcation diagram. However, turbulent noise added to the vocal-fold model would induce chaotic vibrations, broaden the regions of irregular vocal fold vibrations, and inhibit the fine period-doubling bifurcations in the bifurcation diagrams. The perturbations from neurological and biomechanical effects were simulated as a random variation of the vocal fold stiffness. Turbulent noise as an external random source, as well as random stiffness perturbation as an internal random source, played important roles in the presence of irregular vocal fold vibrations.

High-speed digital imaging of the medial surface of the vocal folds.

High-speed digital imaging of the medial surface of the vocal folds was performed in excised canine larynx experiments. Building on the excised larynx investigations of Baer [Ph.D. dissertation, MIT, Boston, MA (1975)] and hemilarynx investigations of Jiang and Titze [Laryngoscope 103, 872-882 (1993)], nine vocal fold fleshpoints were tracked simultaneously along the medial surface of one coronal plane of the left vocal fold using a Kodak EktaPro 4540 high-speed digital imaging system. By imaging from two distinct views, 3D reconstructions of fleshpoint trajectories were performed with a sampling frequency of 4.5 kHz and a spatial resolution of approximately 0.08 mm. Quantitative results were derived from a typical example of periodic chestlike vibrations. Furthermore, these data were decomposed into empirical eigenfunctions, the building blocks of vocal fold vibration, illuminating basic mechanisms of self-sustained oscillation. Previously, such mechanisms have only been explored theoretically using computer models of vocal fold vibration [Berry et al., J. Acoust. Soc. Am. 95, 3595-3604 (1994)]. Similar to the theoretical studies, two eigenfunctions captured 98% of the variance of the data. Because this investigation utilized high-speed technology, the methodology may also be used to examine complex, aperiodic vibrations. Thus, this technique allows mechanisms of regular and irregular vocal fold vibration to be explored using direct observations of vibrating tissues in the laboratory.

Modeling of chaotic vibrations in symmetric vocal folds.

The chaos mechanism of above-range phonation was examined in symmetrically modeled vocal folds by using the traditional two-mass model assumption. The Poincaré map technique was used to display chaotic attractors. This method provided an effective description of irregular vocal-fold movements. The power spectrum, Lyapunov exponent, and Kaplan-Yorke dimension were employed to describe chaotic vibrations in the vocal-fold model. These nonlinear dynamic analyses suggested that, for the positive Lyapunov exponent, chaotic attractors contribute to irregular vocal-fold vibrations. Descriptions of complicated irregular vibrations of the vocal fold yielded evidence of chaos. To investigate the effects of independent parameters such as subglottal pressure, coupling stiffness, and phonation neutral area, bifurcation diagrams based on the Poincaré map were discussed. The results confirmed that the dynamics of the two-mass model was strongly influenced by independent parameters. Nonlinear dynamic methods were expected to provide useful information for better understanding of irregular vocal-fold vibrations as well as of the dynamic mechanism of above-range phonation in excised larynx experimentation.

Deviant Vocal Fold Vibration as Observed During Videokymography: The Effect on Voice Quality

Videokymographic images of deviant or irregular vocal fold vibration, including diplophonia, the transition from falsetto to modal voice, irregular vibration onset and offset, and phonation following partial laryngectomy were compared with the synchronously recorded acoustic speech signals. A clear relation was shown between videokymographic image sequences and acoustic speech signals, and the effect of irregular or incomplete vocal fold vibration patterns was recognized in the amount of perceived breathiness and roughness and by the harmonics-to-noise ratio in the speech signal. Mechanisms causing roughness are the presence of mucus, phase differences between the left and right vocal fold, and short-term frequency and amplitude modulation. It can be concluded that the use of simultaneously recorded videokymographic image sequences and speech signals contributes to the understanding of the effect of irregular vocal fold vibration on voice quality.

Functional imaging of vocal fold vibration: Digital multislice high-speed kymography

For the diagnosis of voice disorders, and especially for the classification of hoarseness, direct observation of vocal fold vibration is essential. Furthermore, a quantitative description of the movement of the vocal fold becomes increasingly necessary to document and compare findings as well as the progression of speech therapy. On the base of digital high-speed sequences of vocal fold vibration, multiple "functional images"-also called digital kymograms-are obtained using image- and signal-processing algorithms. Digital kymograms can serve as a powerful aid for visualization, description, and classification of vocal fold vibration and as an intermediate step for image interpretation by biomechanical modeling. This visualization technique will be discussed and compared to other techniques currently available: videokymography and videostroboscopy. The technique is applied to several clinical examples: aperiodic processes (phonation onset), irregular vocal fold vibration (paralysis of the recurrent nerve), particular vibration modes (anterior-posterior modes), and running speech.

Videokymography: research and clinical issues

Stroboscopy is based on the assumption that the vibration is stable and regular. Irregular vibrations, as is often the case in voice pathology, cannot easily be studied by stroboscopy. Videokymography overcomes this drawback. Videokymography, using a modified CCD video camera, makes it possible to observe all kinds of regular and irregular vocal fold vibrations, including those leading to pathological voice productions, It easily visualises small left-right asymmetries, open and closed phases of the selected part of the glottis, lateral propagation of mucosal waves, movements of the upper margin and, in the closing phase, the lower margin of the vocal folds. This is advantageous for a more accurate diagnosis of voice disorders. Also other fields which study mechanical vibrations, like strings of musical instruments, may benefit from videokymography.

Endoscopic imaging of vocal cord vibrations. Digital high speed recording with various systems

Vocal fold vibration patterns during phonation are presented with different digital imaging systems. With newly developed technical equipment color images up to 1000 digital images/s were obtained without light intensifying enhancement techniques via rigid and flexible endoscopy. With this color high-speed system, morphologic structures, such as small blood vessels, were visualized in high-resolution quality as a result of additional color information. In another system, zooming of endoscopic pictures via pixel interpolation algorithms provided full-monitor presentation of vocal fold vibratory patterns. This system allows PC-based synchronization with microphone and electroglottographic signals in a frame-by-frame technique. Although only processing gray scale images, analyses of dynamic changes in modes of vibration were facilitated by the higher frame rate recording of up to 2000 frames/s and, in addition, they display corresponding analog signals. Both methods provide clinically important information. Furthermore, we demonstrated irregular vocal fold vibration patterns in a healthy adult volunteer. In this experiment, the irregular vibratory modes were induced by voluntarily applying asymmetric vocal fold tension. The asymmetric vocal fold vibration pattern resulted in (functionally induced) roughness of the voice as predicted by computer models of asymmetric vocal fold vibration. Digital high-speed cinematography proved to be a highly promising technique in the analysis of dysphonia and provided physiological examples that could be compared with models of coupled nonlinear oscillators.