Effects of simulated source of tremor on acoustic and airflow voice measures.

To test the effects of different sources of tremor on the voice, tremor was simulated by external rhythmic perturbation of structures at the subglottal, glottal, and supraglottal levels in 10 healthy subjects. The acoustic and airflow signals simultaneously recorded during sustained phonation in the normal and the 3 simulated tremor conditions were analyzed and compared. Voice measures included: fundamental frequency, 2 short-term perturbation measures (jitter and shimmer), and 3 long-term tremor measures (prominence ratios of the spectral peaks of the acoustic frequency contour, acoustic amplitude contour, and airflow contour). Measures of fundamental frequency and percent shimmer were not significantly affected by the simulated tremors. Measures of percent jitter and the amplitudes of the long-term frequency and amplitude modulations were most prominently increased when respiratory drive was perturbed by simulated tremor. Spectral analysis of the acoustic amplitude contour was most useful in distinguishing the 3 sites of simulated tremor.