Acoustic Tracking of Pitch, Modal, and Subharmonic Vibrations of Vocal Folds in Parkinson’s Disease and Parkinsonism

The prominent and early presence of dysphonia is considered a valuable marker for differentiation of idiopathic Parkinson's disease and parkinsonian syndromes. Objective quantification of vibrational regimes represented by modal and subharmonic vibrations may thus be vital for improving accuracy of diagnostic decision. The rationale for analyzing vibrational regimes is that abnormal subharmonic vibrations might be the key factor causing dysphonia in parkinsonian syndromes. This study introduces a new fully automated methodology based on robust pitch tracker for decoupling vibrations controlled by laryngeal muscles from the effect of subharmonics that provides distinguishing features of Parkinson's disease and atypical parkinsonian syndromes. We tested the method on resynthesized signals with known parameters and demonstrated that vibrations controlled by laryngeal muscles as well as subharmonics can be detected reliably with a precision that outperforms available technologies. We analysed 337 sustained vowels of 22 patients with PD, 21 patients with multiple system atrophy, 18 patients with progressive supranuclear palsy and 22 healthy controls. Our results showed that subharmonics are more prominent in atypical parkinsonian syndromes compared to Parkinson's disease. Also, increased modulation by laryngeal muscles appears to be a distinctive symptom of multiple system atrophy. Developed algorithm and proposed resynthesized voice signals provide further critical step to understanding and evaluation of dysphonia in Parkinsonism.