Douglas W. Montequin

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.

Functional outcomes of reduced hyaluronan in acute vocal fold scar.

To examine the functional effects of hyaluronan and collagen alterations in acute vocal fold scar, we injured 15 pig larynges by vocal fold mucosa stripping. At 3, 10, and 15 days after operation, we performed excised larynx experiments to measure phonation threshold pressure (PTP) and vocal economy (an acoustic output-cost ratio; OCR), and then performed hyaluronan and collagen assays. Five uninjured larynges were used as excised controls. Hyaluronan was reduced in the scarred vocal folds through 15 days of wound healing. Collagen was increased at day 15. The PTP was increased and OCR was decreased in scarred larynges, indicating decreased vocal efficiency and ease of phonation. Thus, PTP and OCR were sensitive to the biomolecular changes in acute vocal fold scar. Hyaluronan was more susceptible than collagen to acute tissue ultrastructural alterations. These findings may provide a rationale for increasing hyaluronan in acute vocal fold scar to improve postoperative vocal outcomes.

Aerodynamic Profiles of a Hemilarynx with a Vocal Tract

The pressure-flow relationship was examined in excised canine and human larynges with and without a vocal tract. Canine and human larynges were prepared and cut in the midsagittal plane from the top to about 10 mm below the vocal folds. The right half was removed and replaced with an acrylic plate. The vocal tract was simulated initially with a 15-cm plastic tube and later with a vocal tract model with an area function resembling “ah.” Simultaneous recordings were made of the glottal pressure, mean subglottal pressure, and average airflow at various levels of adduction. Preliminary data indicated that the pressure-flow relationships were similar to those of a full larynx and were almost linear. The addition of the vocal tract increased the glottal resistance by moving these pressure-flow lines to the lower-flow and higher-pressure region. The human larynx appears to phonate more easily than the canine larynx on the laboratory bench and has lower phonation threshold pressures.

An Investigation of Cricoarytenoid Joint Mechanics Using Simulated Muscle Forces

Rotational and translational stiffnesses were calculated for arytenoid motion about the cricoarytenoid joint. These calculations were obtained from measurements on five excised human larynxes. For each larynx, known forces were applied to the arytenoid cartilage, and three markers were tracked as a function of applied forces. Assuming rigid body motion, arytenoid translations and rotations were computed for each applied force. Translational stiffnesses were obtained by plotting force versus displacement, and rotational stiffnesses were calculated by plotting torque versus angular rotation. A major finding was that the translational stiffness along the anterior-posterior direction was three times as great as the translational stiffnesses in the other two directions. This nonisotropic nature of the stiffnesses may be an important consideration for phonosurgeons who wish to avoid subluxation of the cricoarytenoid joint in patients. The computed rotational and translational stiffnesses currently are being implemented in 2D and 3D models. These stiffness parameters play a vital role in prephonatory glottal shaping, which in turn exerts a majorinfluence on all aspects of vocal fold vibration, including fundamental frequency, voice quality, voice register, and phonation threshold pressure.

Characterization of the Medial Surface of the Vocal Folds

A method is developed for the quantification of the medial surface of the vocal folds in excised larynges. Lead molds were constructed from the glottal airway of a canine larynx for 3 distinct glottal configurations corresponding to “pressed” folds, just barely adducted folds, and 1-mm-abducted folds as measured between the vocal processes. With a high-resolution laser striping system, the 3-dimensional molds were digitally scanned. Low-order polynomials were fitted to the data, and goodness-of-fit statistics were reported. For all glottal configurations, a linear variation (flat surface) approximated the data with a coefficient of determination of 90%. This coefficient increased to roughly 95% when a quadratic variation (curvature) was included along the vertical dimension. If more than the top 5 mm or so of the folds was included (the portion usually corresponding to vibration), a cubic variation along the vertical dimension was necessary to explain a change in concavity at the conus elasticus. These findings suggest the utility of a model based on a convergence coefficient and a bulging coefficient. For all glottal configurations, the convergence coefficients and bulging coefficients can be computed. Because pre-phonatory conditions have a profound influence on vocal fold vibration and on the quality of phonation, such shaping parameters are highly significant. With the viability of this method substantiated, it is envisioned that future studies will characterize greater quantities of glottal shapes, including those of human vocal folds.

Contrasting chest and falsettolike vibration patterns of the vocal folds

Using excised larynges, a hemilarynx methodology was used in order to view vocal fold vibrations from a medial aspect. This was accomplished by removing one fold, inserting a glass plate at the glottal midline, and mounting the remaining fold against the glass plate. A stereoscopic imaging system was used to perform 3D tracking of small markers (microsutures) placed on the folds. Chest and falsettolike vibrations patterns were imaged and quantified. These two vibrations patterns will be contrasted with each other, and discussed in terms of previous qualitative comparisons of these phonation types in the literature. [Work supported by Grant No. R29 DC03072 from the National Institute on Deafness and Other Communication Disorders.]

08:10: A Rat Excised Larynx Model of Vocal Fold Scar

broblasts in the scaffold were observed, with active protein synthesis and release. Viscoelastic shear properties of the scaffold were similar to those of the human vocal fold lamina propria. CONCLUSION: These findings supported the biocompatibility of the HUV scaffold and its potential in vocal fold tissue engineering applications. SIGNIFICANCE: Acellular biological scaffolds can promote a natural remodeling response for the reconstruction and regeneration of the vocal fold ECM, ideal for the phonosurgical replacement of lamina propria deficiencies and scars. Having the appropriate biomechanical properties conducive to phonation is a distinct advantage. SUPPORT: This work was supported by NIH Grant no. R01 DC006101.

Vocal tract influence on medial surface dynamics of the vocal folds

In previous work, quantitative measurement of the medial surface dynamics of the vocal folds was reported using a hemilarynx methodology. The technique was applied to excised larynges from both humans and canines, as well as to in vivo canine larynges. In the present investigation, a vocal tract was attached to the excised hemilarynx preparation, and systematic changes were made in vocal tract shape to study its influence on the medial surface dynamics. In particular, the width of the epilarynx was varied across experiments. Previously, in a similar experiment, phonation threshold pressure was investigated as a function of epilarynx width. It has also been shown that epilarynx width has an influence on glottal volume velocity and the acoustic output [I. R. Titze and B. H. Story, J. Acoust. Soc. Am. 101, 2234–2243]. However, the direct influence of the epilarynx width on vocal fold vibration has never been quantified. The present investigation considered the impact of epilarynx width on the medial surface ...

A high‐speed methodology for comparing phonosurgical outcomes in an excised larynx model

Many phonosurgical techniques have been used to treat hoarseness resulting from vocal disease, such as unilateral vocal fold paralysis. However, because of difficulty in documenting changes in mucosal wave propagation, comparing the outcomes of different phonosurgical techniques presents a formidable challenge. The purpose of this investigation is to compare two phonosurgical treatments of unilateral vocal fold paralysis, thyroplasty type 1 and arytenoid adduction, in terms of their impact on the mucosal wave. For thyroplasty type 1, the pushing force was systematically varied. For arytenoid adduction, the pulling forces were systematically varied. Across all experiments, systematic changes were also made in the subglottal pressure, glottal airflow, pre‐phonatory posturing, and in the size of the glottal chink. Because stroboscopic methods could not image properly the aperiodic vibrations associated with paralysis, a digital high‐speed imaging system was utilized (the Kodak EktaPro 4540). Using this syste...