Abstract

This study was designed to longitudinally investigate the extent of phonatory variability in the voices of untreated (speech) patients with idiopathic Parkinson's disease and to document the effect of learning in this group of subjects. Microphone recordings were made from fourteen patients over time to measure the following acoustic variables: maximum duration sustained phonation (in seconds: secs), maximum fundamental frequency range (in semitones: st), mean fundamental frequency range (in Hertz: Hz) and fundamental frequency variability (in semitone standard deviation: stsd) in reading. During the course of the study none of the subjects received speech or voice therapy. Growth curve models were constructed to simultaneously estimate a constant rate of decline of the variables over time (excluding the influence of baseline values) and to estimate the effect of learning due to baseline assessments.

Statistically significant constant decline in weighted mean values were found to exist over time on the variables maximum and mean duration of sustained vowel phonation, maximum and mean fundamental frequency range and mean fundamental frequency variability in reading. The results of this study reveal not only describe longitudinally the phonatory variability among this group of subjects, but also quantify the declining nature of that variability. In addition, a strong learning experience as a result of the baseline assessment was documented. A significant learning effect existed for all variables except fundamental frequency variability in reading. Furthermore, the extent to which learning continues after baseline assessment may actually underestimate the magnitude of normal decline in untreated patients with Parkinson's disease.

These consolidated, longitudinal descriptive data for these fourteen untreated subjects pro vide, 1) additional insight into the continuum of pathophysiologic changes that occur in the phonatory mechanisms of these patients, and 2) a point of reference for comparative studies from which to gauge the magnitude of treatment differences (and potential carryover) over the same time intervals for treated patients with Parkinson's disease.

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