Exploring the phonatory effects of external superior laryngeal nerve paralysis: an in vivo model

Little is known regarding the phonatory consequences of unilateral external superior laryngeal nerve (ESLN) paralysis. By selectively blocking the ESLN with lidocaine HCl (with laryngeal electromyography verification), we modeled acute, unilateral cricothyroid (CT) muscle dysfunction to explore possible acoustic, aerodynamic, auditory-perceptual and auto-perceptive effects.

Prospective, repeated measures, experimental design.

Ten, vocally-normal adult males underwent lidocaine block of the right ESLN. Multiple measures of phonatory function across a variety of vocal tasks/conditions were acquired before and during the block using standard data acquisition and analysis protocols.

During ESLN block, phonatory frequency range was significantly reduced with compression of both upper and lowermost regions of the pitch range. Mean speaking fundamental frequency increased significantly during oral reading. Acoustic analysis, aerodynamic assessment, and auditory- perceptual evaluation by blinded listeners revealed modest increases in phonatory instability (jitter), increased laryngeal airway resistance with no objective evidence of glottic insufficiency, and mild deterioration in voice quality most evident during high pitched voice productions, respectively. Participants uniformly rated their speaking and singing voices as worse during the block with significant weakness, effort, and tightness that they perceived as a mild level of impairment.

These data support generally mild changes to the speaking voice, which extend beyond reductions in pitch range only, and shed light on the potential untoward phonatory effects of acute, unilateral CT dysfunction.