Search

Background Many authors have studied adult’s larynx modelization, but the mechanisms of newborn’s voice production have very rarely been investigated. After validating a numerical model with acoustic data, studies were performed on larynges of human fetuses in order to validate this model with aerodynamical experiments. Material and methods Anatomical measurements were performed and a simplified numerical model was built using Fluent ® with the vocal folds in phonatory position. The results obtained are in good agreement with those obtained by laser Doppler velocimetry (LDV) and high-frame rate particle image velocimetry (HFR-PIV), on an experimental bench with excised human fetus larynges. Results It appears that computing with first cry physiological parameters leads to a model which is close to those obtained in experiments with real organs.

Voice of patient with unilateral laryngeal paralysis (ULP) shows a nonlinear behaviour with sudden octave jumps, bifurcations and chaos. Such a behaviour may be due to an increased number of freedom degrees in the glottal system. We hypothesized that voice intensity (with increasing sub glottal pressure) could improve vocal signal stability with less freedom degrees in vibrating system, and then a decrease of nonlinearities. A prospective study of 32 consecutive voices of patients with ULP and severe dysphonia was conducted. Jitter and Lyapunov exponent from vocal signals were compared at comfortable and loud voicing with Wilcoxon’s test. In 23 out of 32 patients, jitter significantly decreased from 5 (median) in normal voice to 1.2 in loud voice (P < 10−3), Lyapunov exponent decreased from 1,495 bit/s (median) to 708 bit/s (P < 10−4). Two patients had paradoxical results regarding jitter (higher in loud voice) and 2 regarding Lyapunov exponent. From the 23 cases of voice improvement, 15 cases showing a marked improvement of the acoustic analysis supported our hypothesis (65%). Nonlinear phenomena detected in vocal signals of ULP with severe dysphonia may be reduced in loud voice.

This study describes a novel system allowing the noncontact measurement of vibration of each vocal fold. The system is based on reflectometry, i.e. measurement of light bouncing off a vibrating object. The system works in natural light and is sensitive, compact, and inexpensive. We have used this system for separate and simultaneous detection of the vibration of each vocal fold in excised porcine larynges. Normal conditions of vibration and asymmetry of tension leading to biphonations were studied. Analysis of each vibrating cycle reveals interaction between the vocal folds allowing synchronous vibration despite their physical asymmetry or episodes of period doubling.

Summary Coupling between the vocal folds is one of the nonlinear mechanisms allowing regulation and synchronization of mucosal vibration. The purpose of this study was to establish that modulations such as diplophonia and abnormalities observed in vocal signals that may be observed in some cases of laryngeal pathology can be considered as nonlinear behavior due to the persistence of some physical interaction (coupling). An experimental model using excised porcine larynx was designed to create tension asymmetry between the vocal folds and to obtain vocal signals with modulations. Signals were analyzed by spectral analysis and the phase portrait method. Results were compared with computer-generated synthetic signals corresponding to nonlinear combinations of sinusoid signals. Under these conditions, evidence of nonlinear behavior was detected in 85% of experimental signals. These findings were interpreted as a demonstration of vocal fold interaction. Based on these findings, the authors conclude that (1) coupling must be taken into account in physical models of laryngeal physiology, and that (2) methods of nonlinear dynamics may be used for objective voice analysis.

Summary Well-known multimass models of vocal folds are useful to describe main behavior observed in human voicing but their principle of functioning, based on harmonic oscillation, may appear complex. This work is designed to show that a simple one-mass model ruled by laws of relaxation oscillation can also depict main behavior of glottis dynamic. Theory of relaxation oscillation is detailed. A relaxation oscillation model is assessed through a numerical simulation using conventional values for tissue characteristics and subglottal pressure. As expected, raising the mass decreases the fundamental frequency and increases the amplitude of vocal fold vibration: for a mass ranging from 0.01 to 0.4 g, F 0 decreased from 297.5 to 42.5 Hz and vibrational amplitude increased from 1.26 to 3.25 mm (for stiffness k = 10 N m −1 , damping r = 0.015 N s m −1 , and subglottal pressure = 1 kPa). Stiffness value has the opposite effect. The subglottal pressure controls the fundamental frequency with a rate ranging from 20 to 50 Hz/kPa. The vibrational amplitude is also controlled linearly by subglottal pressure from 0.22 to 0.26 mm/kPa. The range of phonation threshold pressure (PTP) is close to the values currently proposed, that is, 0.1 to 1 kPa and varies with the fundamental frequency. The relaxation oscillator is a simple and useful tool for modeling vocal fold vibration.

International audience; Considering on the one hand the important histological differences that exist between newborn and adult vocal folds and on the other hand the specifical subglottal pressure at birth, the sound production in a newborn larynx is studied. The laryngotracheal airflow has been numerically modelled in order to evaluate its role in voice production by the larynx in newborn. The FFT spectrum of the pressure signal acquired just above the vocal folds was calculated and compared to the spectrum of a sound generated by an excised larynx. It can be determined that first, the computed pressure signal has a fundamental frequency close to that obtained experimentally with an excised larynx, and second the FFT spectra are qualitatively similar to one another. Third, the computed pressure fluctuation is strong enough to be detected by the human ear. The conclusion is that the airflow and the aerodynamical phenomena observed in a rigid geometry are, by themselves, able to produce a sound and consequently, are one of the several elements leading to sound production in the newborn larynx. #

Objective The aim of this study was to describe and analyze the vibratory pattern of vocal folds in an asymmetric situation. Study design and setting Cricothyroid muscle unilateral action was simulated on excised larynges on an experimental bench. Increasing airflow rates were applied to achieve vocal fold vibration. Electroglottography and an optoreflectometer device allowed analysis of separate and simultaneous vocal fold vibration. Spectra of the signals were obtained for each level of airflow variation. Results All experiments showed periodic vibration. A phase shift was noted between the two vocal folds. Subharmonics and biphonation were identified in all the experiments. Conclusion Lax vocal folds were more susceptible to spectral changes with increasing airflow. Significance Knowledge of the consequences of mass, tension, and position asymmetries of the vocal folds is crucial for diagnosis making and defining therapeutic strategies in dysphonic patients. This study may contribute to the understanding of physiology of vocal fold interaction and its compensatory mechanisms.

Summary Numerous clinical findings indicate that viscosity of laryngeal mucosa is a crucial factor in glottal perfomance. Experience using experimental test benches has shown the importance of humidifying air stream used to induce vibration in excised larynges. Nevertheless, there is a lack of knowledge particularly regarding the physicochemical properties of laryngeal mucus. The purpose of this study was to research vocal fold vibration in excised larynges using artificial mucus of precisely known viscosity. Eight freshly harvested porcine larynges were examined. Parameters measured were Fo and vocal fold contact time. Measurements were performed under three conditions: basal (no fluid application on vocal cord surface), after application of a fluid of 60cP viscosity (Visc60), and after application of a fluid of 100cP viscosity (Visc 100). Electroglottographic measurements were performed at two different times for each condition: 1 s after airflow onset (T1) and 6 seconds after airflow onset (T2). Statistical analysis consisted of comparing data obtained under each condition at T1 and T2. The results showed a significant decrease in Fo after application of Visc60 and Visc100 fluids and a decrease in Fo at T2. Closure time was significantly higher under Visc60 conditions and under Visc100 conditions than under basal conditions. Application of artificial mucus to the mucosa of the vocal folds lowered vibratory frequency and prolonged the contact phase. Our interpretation of this data is that the presence of mucus on the surface of the vocal folds generated superficial tension and caused adhesion, which is a source of nonlinearity in vocal vibration.

We investigated the possibility of obtaining an anteroposterior body response to galvanic vestibular stimulation (GVS) by applying an equivalent stimulus to both sides of the vestibular apparatus. An original ‘double fronto-mastoidal’ stimulation was used on eight subjects standing with their head facing forwards. Both the onset and the cut-off of the current did induce an anteroposterior body tilt, without any lateral component. The amplitude of the tilt increased as a function of stimulus intensity. GVS evokes anteroposterior or lateral sway of similar spatio-temporal features according to the stimulation configuration. We suggest that the central nervous system makes use of the discrepancy between the left and right vestibular activity to orientate the response: equivalent afferent flows would result in an anteroposterior body response whereas lateral sway is obtained with discrepant ones. © 1998 Elsevier Science Ireland Ltd.