Vocal Fold Dissipated Power in Females with Hyperfunctional Voice Disorders

Phonotrauma has been hypothesized to be associated with prolonged and/or accumulated biomechanical stress on vocal fold tissue. This hypothesis can be tested using ambulatory monitoring of vocal fold dissipated power, which requires a reliable method for its noninvasive estimation during the activity of daily living. The first aim of this study was to show that a laboratory-based estimate of vocal fold dissipated power computed from intraoral pressure (IOP) has significant discriminative power in individuals with phonotraumatic vocal hyperfunction (PVH). Considering that estimation of subglottal pressure from IOP is not practical for ambulatory applications, an alternative approach should be used. The second aim of this study was to test the impact of two alternative methods for the estimation of subglottal pressure on the discriminative power of vocal fold dissipated power in individuals with PVH and, hence, to provide an evidence-based recommendation for future ambulatory monitoring studies of vocal fold dissipated power.

Four groups of adult females were included in this study: 16 individuals with PVH, 16 individuals with nonphonotraumatic vocal hyperfunction (NPVH), and two groups of vocally typical controls matched to the participants in each patient group in terms of age and occupation. Each participant produced strings of five consecutive /pae/ syllables while wearing a pneumotachograph mask with an IOP tube. Neck-surface accelerometer and acoustic signals were recorded simultaneously using an ambulatory voice monitor and a head-mounted microphone, respectively. IOP was used to estimate subglottal pressure and subject-specific calibration factors were determined for the estimation of subglottal pressure from the accelerometer signal.

(1) Individuals with PVH had significantly higher dissipated power than controls (P = 0.001, Cohen's D=1.31) when the intraoral estimate of subglottal pressure was used in the computation of dissipated power. (2) The difference between the dissipated power of individuals with NPVH and their matched controls was not significant. (3) When microphone-based sound pressure levels was used for the estimation of subglottal pressure, the difference between individuals with PVH and their matched controls vanished (P = 0.23). (4) When subject-specific estimation of subglottal pressure from the accelerometer was used, the discriminative power returned with a very large effect size (P = 0.001, D=1.38).

Increased dissipated power is sensitive and specific to individuals with PVH among individuals with hyperfunctional voice disorders. The results provide evidence that accelerometer-based estimate of energy dissipation dose (power integrated over time) during daily life could be clinically useful.