Abstract
Acoustic and electroglottographic measures were used to quantify the effects of drug cycle fluctuations, specifically the on-off effect and dyskinesias, on phonation in two subjects with Parkinson's disease. Analysis of maximum sustained and comfortable vowel phonations indicated phonatory instabilities and variability and in creased glottal adduction were present in both subjects. Also, a systematic and consistent relationship between drug cycle fluctuations and phonatory measures was not observed, but there was evidence to suggest that short term perturbation measures (shimmer and jitter) vs. long-term perturbation measures (coefficient of variation of amplitude and frequency) were more sensitive to drug treatment effects and that phonatory function was more similar to limb responses during on-off vs. dyskinetic states. Potential mechanisms underlying these findings are discussed.

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