MECHANISM OF GLOTTIC CLOSURE IN A MODEL OF UNILATERAL VOCAL FOLD PALSY

The effect of extrinsic laryngeal muscles on the position of the paral yzed vocal fold (VF) was analyzed in 13 adult human larynges. Fresh sp ecimens were suspended within a specially constructed frame designed t o reproduce the three-dimensional position of the VF, and to allow for simulation of laryngeal muscle action, in five successive experiments resembling: 1) complete vagal paralysis and contralateral adduction, 2) laryngeal elevation added, 3) vocal fold stretching added, 4) contr alateral laryngeal tilting added, and 5) ipsilateral cricothyroid musc le activation added. We observed an incremental narrowing of the middl e and posterior glottic gaps from 3.9 mm and 6.8 mm respectively in ex periment 1 to 1.1 mm and 1.9 mm in experiment 5. Glottic closure in th e final experiment was associated with rotation of the glottis to the ''paralyzed'' side in the axial plane, and contralateral laryngeal til ting in the coronal plane. We show that extrinsic laryngeal muscles ca n help to close a paralytic gap; crossing of the contralateral VF past the midline was not observed in any of the experiments.