Physiologic and acoustic patterns of essential vocal tremor

Objectives/Hypothesis: This article describes a case study of physiologic and acoustic patterns of essential vocal tremor (EVT). Simulations of vocal tremor were used to test hypotheses regarding measured acoustic patterns and expected physiologic sources. Study Design: This is a case study of EVT using an analysis by synthesis approach. Methods: Oscillations of vocal tract and laryngeal structures were identified using rigid videostroboscopic examination. Acoustical analyses of sustained phonation were completed using the methods previously described in the literature and custom-written MATLAB functions. Simulations of the client's vocal tremor were created using a computational model. Results: The client exhibited vocal fold length changes and oscillation within the laryngeal vestibule during sustained phonation at a comfortable pitch and loudness. Despite the involvement of vocal fold length changes, a low average extent of fundamental frequency (F₀) modulation (ie, 5.3%) and high average extent of intensity modulation (ie, 23.0%) were measured. Simulations of vocal tremor involving modulation of F₀ demonstrated that this source of tremor contributes to frequency-induced intensity modulation, although there was a greater extent of F₀ modulation than intensity modulation. Conclusions: The greater extent of intensity than F ₀ modulation in one client with EVT exhibiting predominant vocal fold length changes contrasted with the lower extent of intensity than F₀ modulation in simulated vocal tremor involving F₀ modulation. These findings demonstrate that other potential sources of intensity modulation outside the larynx should be determined during the evaluation of clients with vocal tremor.