Vocal fold vibration viewed from the tracheal side in living human beings

The mucosal upheaval where the mucosal wave starts and propagates upward appears on the lower surface of the canine vocal fold during vibration. We investigated the vibratory behavior of the in vivo human vocal fold viewed from the tracheal side. Subjects consisted of 14 men and 6 women who had undergone tracheostomy for various head and neck diseases; their ages ranged from 22 to 70 years, with a mean of 53.9 years. The inferior aspect of the vocal fold during phonation was observed with the aid of a rigid oblique-view endoscope inserted through a tracheostoma (inferior glottoscopy). Each subject was asked to sustain the vowel /a/ at a comfortable pitch and loudness (easy phonation) and then at a higher pitch. Inferior glottoscopy could be performed during easy phonation in 19 subjects and during high-pitched phonation in 10 subjects. During easy phonation, the mucosal upheaval appeared on the lower surface of the vocal fold between the anterior commissure and the vocal process in all 19 subjects. During high-pitched phonation, the vocal fold became longer, and the subglottic vault surrounded by the bilateral mucosal upheavals became narrower compared with those during easy phonation. Use of a dilated blood vessel as a landmark in one subject showed the location of the mucosal upheaval on the vocal fold mucosa to actually shift medially toward the oral side during high-pitched phonation. Despite structural differences between the human and canine vocal folds, the infraglottic aspect of the vocal fold vibration observed in the living human larynx was quite similar to that observed in the excised canine larynx.