The Relationship Between Vortices, Acoustics, and Vibration in Vocal Fold Asymmetries

Project summary. Common operations for unilateral vocal fold paralysis (UVFP), such as Thyroplasty Type 1, improve vocal efficiency (VE) by closing the membranous gap between the normal and paralyzed fold. VE measures the degree to which subglottal aerodynamic power is translated to acoustic power. However, even after surgical treatment, some patients report symptoms such as vocal fatigue, decreased projection, and decreased intelligibility in noisy environments. These recalcitrant symptoms will be associated with reduced VE relative to normal voice, suggesting that enhancing VE could further ameliorate these symptoms. Our previous work in the excised canine larynx suggests that this further improvement is possible by certain modifications to the procedure. For example, we found the surprising result that medialization of the tissue below the fold (infraglottal region) results in higher VE than medialization of the fold itself (glottal) even though both operations close the medial-lateral membranous gap. Additionally, inclusion of arytenoid adduction increased VE relative to infraglottal medialization alone. However, to translate these surgical findings in animals to patients requires a deeper understanding about how and why various treatment modifications affect VE. In prior work we found that rotational motion (vortices) occur between the folds during closing. These vortices produce negative pressures that cause the folds to close together faster, which increase acoustic intensity and VE. We know that the bottom part of the folds is stiffer than the upper part; this is referred to as the vertical stiffness gradient (VSG). We have also found that lower VSG produces weaker vortices and decreased VE. In the first aim, we will further examine the effect of the VSG on VE. In the second and third aim, we will look at how and why different treatments for UVFP affect VE. This application lays the foundation for using VE clinically, and for optimizing clinical treatments for UVFP.