Decreasing the closing speed of the vocal folds can reduce loudness and energy in the higher frequency harmonics, resulting in reduced voice quality. Our aim was to study the correlation between higher frequencies and the intraglottal vorticity (which contributes to rapid closing by producing transient negative intraglottal pressures).
Using six excised canine larynges (three with symmetric and three with asymmetric, periodic vocal fold motion), intraglottal vorticity was calculated from 2D velocity fields measured using particle imaging velocimetry.
There is a strong correlation between intraglottal vorticity and acoustic energy in the higher frequencies; in periodic asymmetric motion, the vorticity and higher frequencies are both reduced.
For unilateral vocal fold paralysis, these findings suggest one reason why periodic, asymmetric motion, may produce an abnormal voice. Further study will help determine when and why reinnervation, as opposed to medialization, may result in better voice quality. Laryngoscope, 119:216–221, 2009