Thyroarytenoid muscle activity associated with hypophonia in Parkinson disease and aging

Objective: To compare electromyographic (EMG) amplitudes of the thyroarytenoid (TA) muscle in young and older individuals and individuals with idiopathic PD (IPD) under conditions of known vocal loudness (sound pressure level). Background: Voice disorders frequently accompany aging and IPD, but it is unclear how laryngeal muscle physiology is affected by these processes and how changes in laryngeal muscle activity result in characteristic changes of the voice. Methods: Absolute and relative (to maximum) EMG amplitudes of the TA muscle were compared during speech and nonspeech tasks. Corresponding sound pressure level (SPL) measures were obtained for the speech tasks. Results: Absolute TA amplitudes were consistently the highest in the young individuals, lowest in the individuals with IPD, and intermediate in the older individuals. Relative TA amplitudes were generally the highest for the young individuals, lowest for the older individuals, and intermediate for the individuals with IPD, SPL findings showed the older individuals and individuals with IPD produced most of the speech tasks with comparable SPLs, and these levels were consistently lower than those of the young individuals. Conclusions: Reduced levels of TA muscle activity may contribute to the characteristic hypophonic voice disorders that frequently accompany IPD and aging.