Kinematic Features of Laryngeal Motor Control in Parkinson's Disease.

PURPOSE: Laryngeal kinematics were examined under high-speed videoendoscopy to examine laryngeal motor control of persons with Parkinson's disease (PD). METHOD: A retrospective analysis was performed on 24 people with idiopathic PD and 24 age- and sex-matched controls as they produced repetitions of the utterance /ifi/ at self-induced levels of vocal effort (typical, mild, moderate, and maximum effort). Two kinematic measures of laryngeal motor control were measured during vocal fold adduction: spatiotemporal index (STI; adductory variability across repeated utterances) and asymmetry index (AI; ratio of deceleration to acceleration of adduction). Mixed-effects analysis of variance models were constructed to determine the main effects of group (PD, control), self-induced level of vocal effort, and their interaction. RESULTS: Statistically significant main effects of group were found for STI, but not AI. No statistically significant effects of vocal effort level or its interaction with group were observed for either measure. CONCLUSIONS: Larger STIs in people with PD are consistent with the increased production variability observed in other speech articulators. Neither laryngeal kinematic measure was modulated by vocal effort level. These findings indicate that the STI was sensitive to differences in laryngeal motor control impairment between people with and without PD.