Studying vocal fold vibrations in Parkinson’s disease with a nonlinear model

Abstract

A nonlinear model is applied to study pathologic vocal vibratory characteristics and voice treatments of Parkinson's disease. We find that a number of pathologic vocal characteristics commonly observed in Parkinson's disease, including reduced vibratory intensity, incomplete vocal closure, increased phonation threshold pressure, glottal tremor, subharmonics, and chaotic vocal fold vibrations, can be studied with this nonlinear model. We also find that two kinds of clinical voice treatments for Parkinson's disease, including respiratory effort treatment and Lee Silverman voice treatment can be studied with this computer model. Results suggest that respiratory effort treatment, in which subglottal pressure is increased, might aid in enhancing vibratory intensity, improving glottal closure, and avoiding vibratory irregularity. However, the Lee Silverman voice treatment, in which both subglottal pressure and vocal fold adduction are increased, might be better than respiratory effort treatment. Increasing vocal fold thickness would be further helpful to improve these pathologic characteristics. The model studies show consistencies with clinical observations. Computer models may be of value in understanding the dynamic mechanism of disordered voices and studying voice treatment effects in Parkinson's disease.

Acoustic characteristics of phonation in “wet voice” conditions

“…There are a number of similarities between our results and the results of studies on abnormal phonation in pathological voice conditions involving edema, vocal folds polyps, nodules, and cysts, among others ͑Herzel et al., 1994, Berry et al, 1996, Titze, 1994a, Giovanni et al, 1999a, Giovanni et al, 1999b, Švec et al, 1999, Jiang et al, 2003, Zhang and Jiang, 2004, Zhang et al, 2005, Jiang et al, 2006. As in the Jiang et al ͑2003͒ excised experiments, we found that the acoustic signal showed signs of irregular phonation, and that non-linear methods worked better than classic perturbation methods for characterizing baseline versus viscosity conditions.…”

“…A similar explanation may apply to the pathological voices examined by Herzel et al, 1994, Berry et al, 1996, Titze, 1994a, Giovanni et al, 1999a, Giovanni et al, 1999b, Švec et al, 1999, Jiang et al, 2003, Zhang and Jiang, 2004, Zhang et al, 2005, Jiang et al, 2006, and Zhang and Jiang, 2008 In addition, we found that the non-linear measures were particularly sensitive to differences in viscosity. For example, both correlation dimension and the Lyapunov exponent were able to identify difference between thin liquid and honey.…”

“…In recent years, non-linear methods of analysis have been gaining popularity in the study of vocal folds acoustics ͑Mende et al , Herzel et al, 1994, Titze, 1994a, Steinecke and Herzel, 1995, Narayanan and Alwan, 1995, MacAuslan et al, 1997, Giovanni et al, 1999a, Giovanni et al, 1999b, Švec et al, 1999, Jiang et al, 2003, Zhang and Jiang, 2004, Zhang et al, 2005, Jiang et al, 2006. This emphasis on non-linear methods is due to recognition that phonation involves a number of non-linear mechanisms, such as flow-pressure relations, source-tract interaction, flow turbulence, and stress-strain relations within the vocal fold tissue.…”

“…Most of this work has been focused on conditions that result from normal versus abnormal physiology related to laryngeal disease. For instance, there is a long tradition of comparing normal voice production with that from patients with vocal folds polyps, cysts and nodules, vocal folds edema, spasmodic dysphonia, Parkinson disease, and surgical scarring, among others ͑Klingholtz, 1990, Kreiman et al, 1993, Herzel et al, 1994, Giovanni et al, 1999a, Giovanni et al, 1999b, Vieira et al, 2002, Jiang et al, 2006, Zhang et al, 2005. One type of abnormal voice production that has not been well studied is the case of vocal fold vibration when foreign material is present in the laryngeal area.…”

Effects of mucosal loading on vocal fold vibration

“…[3][4][5] Vibration of the vocal folds results from interactions between the vocal folds and multiple factors, including glottal airflow, vocal tract acoustics, and subglottal acoustics. The interaction between glottal airflow and vocal fold tissue is intrinsic to vocal fold vibration.…”