Phonatory effects of supraglottic structures in excised canine larynges.

The aim of this study is to determine how phonation is affected by the presence and by alteration in the position of the supraglottic structures. The study used three excised canine larynges. A series of pressure-flow experiments were completed first on the excised larynx with false folds and epiglottis intact, then with the epiglottis removed, and finally with the false folds removed. Aerodynamic and acoustic effects were quantified with the analysis of the pressure, flow, and audio signals. The results of the study indicated that (1) elevation of the epiglottis to upright position from a horizontal position decreased subglottal pressure, increased flow (decreased laryngeal resistance), and slightly decreased fundamental frequency; (2) vibration of the false vocal folds induced some irregularity into the acoustic output of the larynx; (3) the presence of the epiglottis and the false vocal folds enhanced the second partial of the acoustic signal; and (4) the absence of the epiglottis and false folds increased low-frequency noise (between 0 and 300 Hz). Alteration in the position of the supraglottic structures affects laryngeal aerodynamics and acoustics, possibly due to biomechanical linkage with true vocal folds. When the supraglottic structures are present they act as resonators, enhancing the second partial and when they are absent (as in persons with supraglottic laryngectomy), low-frequency noise is increased perhaps due to the loss of boundary conditions or due to the presence of loose tissue.