Glottal Region Research Articles

Observed intraglottal pressures, their analytic representations, and driving forces for two-mass models

Multimass modeling of phonation should be based on valid aerodynamic characteristics. Measured glottal wall pressures over a wide range of glottal geometries and transglottal pressures were used to obtain average driving forces on the surfaces of two-mass models of phonation. A Plexiglas model of the larynx was used for this purpose. Predictions from the classic equations of Ishizaka and Flanagan were compared to these driving forces and movies of the calculated motions of the two-mass models were produced. The data show that the magnitudes of the negative pressures on the lower glottal region tend to be considerably less than those predicted by the Ishizaka–Flanagan equations, which leads to an increase in the number of cycles (longer time) for the vocal folds to reach steady state, lower peak volume flows, and larger open quotients. Subsequently, analytic expressions were used to represent the intraglottal pressures, with special attention to the entrance losses and the form used to describe the Poisseuille frictional effects, and their accuracy was assessed by a comparison with the measured flow rates and pressures. Results from the analytic representations were compared with those generated from the Ishizaka and Flanagan formulation. [Work supported by NIH Grant No. 2 R01 DC03577.]

Computational aeroacoustics of phonation, part II: Effects of flow parameters and ventricular folds.

The results are described of the second part of an ongoing study aimed at performing direct numerical simulations of translaryngeal flows during phonation. The use of accurate numerical schemes allows the radiated sound to be calculated directly, without the need for acoustic analogy models. The goal is to develop a better understanding of this class of flow, and of the basic sound generation mechanisms involved in phonation. In the present study, the effects of subglottal pressure and of glottal oscillation frequency on the near-field flow and farfield sound were investigated. The effects of the presence of the ventricular folds downstream of the oscillating glottal region were also examined. The results highlighted the effects of subglottal pressure and oscillation frequency on the jet vortical structure, wall pressure and shear stress, and sound radiation. Jet impingement on the ventricular folds introduced additional dipole sources similar to those observed in problems involving grazing flows over cavities.

A method of applying Fourier analysis to high-speed laryngoscopy.

A new method for analysis of digital high-speed recordings of vocal-fold vibrations is presented. The method is based on the extraction of light-intensity time sequences from consecutive images, which in turn are Fourier transformed. The spectra thus acquired can be displayed in four different modes, each having its own benefits. When applied to the larynx, the method visualizes oscillations in the entire laryngeal area, not merely the glottal region. The method was applied to two laryngoscopic high-speed image sequences. Among these examples, covibrations in the ventricular folds and in the mucosa covering the arytenoid cartilages were found. In some cases the covibrations occurred at other frequencies than those of the glottis.

Computational aeroacoustics of phonation: Effect of subglottal pressure, glottal oscillation frequency, and ventricular folds

Numerical simulations of flow and acoustics in an idealized axisymmetric model of the human vocal tract have been conducted. The compressible Navier–Stokes equations were numerically integrated using highly accurate numerical treatments together with a forced glottal oscillation model and a moving grid. The effects of subglottal pressure and glottal oscillation frequency on velocity, vorticity, wall pressure, wall shear stress, and acoustic signal of the pulsating jet were investigated. An acoustic analogy was used to predict the far-field sound. Excellent agreement between the predicted and directly simulated far-field sound was obtained. The acoustic analogy was also used to decompose the acoustic source and identify monopole, dipole, and quadrupole contributions for analyses. The results show significant effects of subglottal pressure and glottal oscillation frequency on the jet vortical structure, wall forces, and acoustic radiation. The effect of including the ventricular (false) folds downstream of the oscillating glottal region was also investigated. Jet impingement on the ventricular folds introduces additional dipole sound sources. [Work supported by NIH DCO 3577-02, RO1 grant from NICDC.]

Acoustic and EM waves for speech processing

The use of low power EM sensors [Holzrichter, Burnett, Ng, and Lea, J. Acoust. Soc. Am. 103, 62 (1998)] enable the determination of several articulator boundary motions, simultaneously—e.g., glottis, jaw, tongue, palate, lips, etc.—leading to new speech processing algorithms. By comparing EM sensor methods of pitch detection to established cepstral and autocorrelation techniques, a tenfold increase in pitch accuracy, a 100-fold reduction in processing time, and robust performance in the presence of high background acoustic noise are obtained. Investigations of the details of the EM sensor signal from the human glottal region indicate that it can be used to provide information on the instant excitation function of voiced speech. Using the ARMA approach, the excitation information is removed from the acoustic signal, yielding well-defined transfer functions, formant locations, and pitch normalized data. In addition, using the glottal timing information, pitch synchronous processing has been employed using ARMA, LPC, Cepstral, and other approximation techniques. The excitation function and the corresponding filter coefficients for each speech unit (e.g., the a’s and b’s from the ARMA approximation) enable one to reconstruct good quality personalized speech, without the need for residual information.

Histamine hyperresponsiveness of the extrathoracic airway in patients with asthmatic symptoms

Functional abnormalities of the extrathoracic airway (EA) may produce symptoms mimicking bronchial asthma. We assessed the bronchial (B) and EA responsiveness to inhaled histamine in 40 patients with asthmatic symptoms and in nine asymptomatic controls. FEV1 and maximal mid-inspiratory flow (MIF50) were used as index of bronchial and EA narrowing. Hyperresponsiveness of the intra-(BHR) or extra-(EA-HR) thoracic airway was diagnosed when the provocative concentrations of histamine (PC20FEV1 or PC25MIF50) were less than 8 mg/ml. Fiberoptic laryngoscopy was performed in nine patients and three controls. The glottal region was measured at mid-volume of maximal inspiration (AgMI) and expiration (AgME) before and after histamine. Predominant EA-HR was found in 13 patients, predominant BHR in 12, equivalent BHR and EA-HR in another 12; no significant airway narrowing was observed in three patients and in the nine controls. EA-HR was significantly associated with female sex, sinusitis, post-nasal drip, dysphonia; BHR with atopy, wheezing and lower MEF50. The percent change in AgMI after histamine was closely related to the PC25MIF50 (r = 0.87, P less than 0.001), that of AgME to the PC20FEV1 (r = 0.78, P less than 0.01). These findings suggest that the assessment of EA responsiveness may be useful in the evaluation of asthmatic symptoms, especially in patients with no BHR.