Aerodynamic and acoustic characterisitics of glottal closure insufficiency

Abstract

Glottal closure insufficiency (GCI) and asymmetric oscillations of the vocal folds are often responsible for low voice quality and increased phonation effort for concerned patients. In this study, four clinically observed types of GCI with increasing glottal closure insufficiency were reproduced in the aero-acoustic computer model simVoice. Each type was simulated with symmetric and asymmetric oscillations extracted from high-speed recordings obtained in ex-vivo porcine larynges. The results show a permanent glottal flow throughout the oscillation cycle and an increasing mean flow rate for increasing minimum glottal gap. Consequently, the aerodynamic work exerted onto the vocal folds decreases for an increasing gap corresponding to the reported patient’s effort increase. Moreover, the quality of the computed sound decreases with an increasing gap based on the cepstral-peak-prominence. Even worse, asymmetric oscillations further degrade both, the aerodynamic energy transfer and the acoustic quality. The temporal evolution of energy transfer shows that the main decay occurs during the opening of the glottis. This shows that the blockage of the flow during glottis closure and the resulting large temporal gradients in pressure and velocity in the larynx are the key features for an efficient phonation process which is also visible in the aero-acoustic sound sources.