Effects of asymmetric vocal fold activation on phonation.

Abstract

The effects of asymmetric vocal fold activation on phonation were studied using an in vivo canine model and graded neuromuscular stimulation of the recurrent laryngeal nerve (RLN). One RLN was stimulated at 21 levels of graded stimulation, from threshold activity to maximal contraction, at three levels of contralateral vocal fold contraction (low, medium, and high). Phonation onset pressure (Pth) was recorded at each condition. The effects of airflow and cricothyroid (CT) muscle activation were studied by varying airflow and CT activation levels. Pth remained relatively constant over nearly all conditions while the level of graded stimulation needed to reach Pth varied. Increasing airflow and higher level of contralateral vocal fold activation allowed Pth to be reached at lower levels of graded stimulation, while activation of CT muscles had the opposite effect. At maximal CT activation, Pth was reached only at high levels of contralateral vocal fold activation but Pth was doubled. Results show that in vocal fold paresis/paralysis, phonation onset can be achieved by increasing either airflow or activation level of the normal vocal fold, and that CT activation increases the phonatory effort. These results provide further insights into the compensatory mechanisms required for phonation in these common laryngeal pathologies.