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Phonation threshold pressure: comparison of calculations and measurements taken with physical models of the vocal fold mucosa.

ABSTRACT: In an important paper on the physics of small amplitude oscillations, Titze showed that the essence of the vertical phase difference, which allows energy to be transferred from the flowing air to the motion of the vocal folds, could be captured in a surface wave model, and he derived a formula for the phonation threshold pressure with an explicit dependence on the geometrical and biomechanical properties of the vocal folds. The formula inspired a series of experiments [e.g., R. Chan and I. Titze, J. Acoust. Soc. Am 119, 2351-2362 (2006)]. Although the experiments support many aspects of Titze's formula, including a linear dependence on the glottal half-width, the behavior of the experiments at the smallest values of this parameter is not consistent with the formula. It is shown that a key element for removing this discrepancy lies in a careful examination of the properties of the entrance loss coefficient. In particular, measurements of the entrance loss coefficient at small widths done with a physical model of the glottis (M5) show that this coefficient varies inversely with the glottal width. A numerical solution of the time-dependent equations of the surface wave model shows that adding a supraglottal vocal tract lowers the phonation threshold pressure by an amount approximately consistent with Chan and Titze's experiments.

SUBMITTER: Fulcher LP

PROVIDER: S-EPMC3188973 | biostudies-other | 2011 Sep

REPOSITORIES: biostudies-other

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Project description:Injuries of the vocal folds frequently heal with scar formation, which can have lifelong detrimental impact on voice quality. Current treatments to prevent or resolve scars of the vocal fold mucosa are highly unsatisfactory. In contrast, the adjacent oral mucosa is mostly resistant to scarring. These differences in healing tendency might relate to distinct properties of the fibroblasts populating oral and vocal fold mucosae. We thus established the in vitro cultivation of paired, near-primary vocal fold fibroblasts (VFF) and oral mucosa fibroblasts (OMF) to perform a basic cellular characterization and comparative cellular proteomics. VFF were significantly larger than OMF, proliferated more slowly, and exhibited a sustained TGF-β1-induced elevation of pro-fibrotic interleukin 6. Cluster analysis of the proteomic data revealed distinct protein repertoires specific for VFF and OMF. Further, VFF displayed a broader protein spectrum, particularly a more sophisticated array of factors constituting and modifying the extracellular matrix. Conversely, subsets of OMF-enriched proteins were linked to cellular proliferation, nuclear events, and protection against oxidative stress. Altogether, this study supports the notion that fibroblasts sensitively adapt to the functional peculiarities of their respective anatomical location and presents several molecular targets for further investigation in the context of vocal fold wound healing.Biological significanceMammalian vocal folds are a unique but delicate tissue. A considerable fraction of people is affected by voice problems, yet many of the underlying vocal fold pathologies are sparsely understood at the molecular level. One such pathology is vocal fold scarring - the tendency of vocal fold injuries to heal with scar formation -, which represents a clinical problem with highly suboptimal treatment modalities. This study employed proteomics to obtain comprehensive insight into the protein repertoire of vocal fold fibroblasts, which are the cells that predominantly synthesize the extracellular matrix in both physiological and pathophysiological conditions. Protein profiles were compared to paired fibroblasts from the oral mucosa, a neighboring tissue that is remarkably resistant to scarring. Bioinformatic analyses of the data revealed a number of pathways as well as single proteins (e.g. ECM-remodeling factors, transcription factors, enzymes) that were significantly different between the two fibroblast types. Thereby, this study has revealed novel interesting molecular targets which can be analyzed in the future for their impact on vocal fold wound healing.

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Phonation threshold pressure: comparison of calculations and measurements taken with physical models of the vocal fold mucosa.

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