Characterization of the medial surface of the vocal folds

A method is developed for the quantification of the medial surface of the v ocal folds in excised larynges. Lead molds were constructed from the glotta l airway of a canine larynx for 3 distinct glottal configurations correspon ding to "pressed" folds, just barely adducted folds, and l-mm-abducted fold s as measured between the vocal processes. With a high-resolution laser str iping system, the 3-dimensional molds were digitally scanned. Low-order pol ynomials were fitted to the data, and goodness-of-fit statistics were repor ted. For all glottal configurations, a linear variation (flat surface) appr oximated the data with a coefficient of determination of 90%. This coeffici ent increased to roughly 95% when a quadratic variation (curvature) was inc luded 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 cubi c 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 a il glottal configurations, the convergence coefficients and bulging coeffic ients can be computed. Because pre-phonatory conditions have a profound inf luence on vocal fold vibration and on the quality of phonation, such shapin g parameters are highly significant. With the viability of this method subs tantiated, it is envisioned that future studies will characterize greater q uantities of glottal shapes, including those of human vocal folds.