Vocal Fold Kinematics and Convergent-Divergent Oscillatory Glottis: Basic Insights Using Mucosal Wave Modeling and Synthetic Kymograms.

Abstract

Purpose: Owing to mucosal waves, the oscillatory glottis is ideally expected to be convergent during opening and divergent during closing. However, this does not necessarily hold for voice disorders. Here, we pave the way for recognizing COnvergent-DIvergent (CODI) waveforms quantitatively and study the kinematic conditions in which they occur.

Method: We simulated 3,125 laryngoscopic glottal waveforms using a kinematic vocal fold (VF) model and synthetic kymograms. We independently varied the oscillatory amplitudes of the upper and lower VF margins, A_U and A_L (0.1 to 1.1 mm), vertical phase difference (VPD; 0° to 125°), glottal halfwidth H_W (-0.05 to 1.2 mm), and prephonatory glottal convergence angle ψ_CVG (-15° to 35°) to simulate normal and disordered conditions. We introduced the upper and lower margin quotients, Q_U and Q_L, quantifying the proportion of time when the upper margin is at the glottal edge during the opening, and when the lower margin is at the glottal edge during the closing, respectively. A CODI waveform was defined as the case when Q_U = Q_L = 1.

Results: The likelihood of obtaining the CODI waveform was highest when A_U and A_L were similar, ψ_CVG was close to 0, H_W was below 0.45 mm, and VPD was larger than 50°. In 88% of the simulated cases, the waveforms did not fulfill the CODI conditions. In these cases, either the lower margin was hidden during some portion of the closing phase or the upper margin was not at the glottal edge during some portion of the opening phase.

Conclusion: The study provides the basis for a better understanding of the variability of glottal waveforms and the appearance of mucosal waves related to VF kinematics.