During phonation, air pressures act upon the vocal folds to help maintain t
heir oscillation. The air pressures vary dynamically along the medial surfa
ce of the vocal folds, although no live human or excised studies have shown
how those pressure profiles vary in time. The purpose of this study was to
examine time-dependent glottal pressure profiles using a canine hemilarynx
approach. The larynx tissue was cut in the midsaggital plane from the top
to about 5 mm below the vocal folds. The right half was replaced with a Ple
xiglas pane with imbedded pressure taps. Simultaneous recordings were made
of glottal pressure signals, subglottal pressure, particle velocity, and av
erage airflow at various levels of adduction. The data indicate that the pr
essures in the glottis (on the Plexiglas) vary both vertically and longitud
inally throughout the phonatory cycle. Pressures vary most widely near the
location of maximum vibratory amplitude, and can include negative pressures
during a portion of the cycle. Pressures anterior and posterior to the max
imum amplitude location may have less variation and may remain positive thr
oughout the cycle, giving rise to a new concept called dynamic bidirectiona
l pressure gradients in the glottis. This is an important concept that may
relate strongly to tissue health as well as basic oscillatory mechanics.