The minimum glottal airflow to initiate vocal fold oscillation.

Phonation threshold flow (PTF) is proposed as a new aerodynamic parameter of the speech production system in this study. PTF is defined as the minimum airflow that can initiate stable vocal fold vibration. Because the glottal airflow can be noninvasively measured, it is suggested that the aerodynamic parameter PTF may be more practical for clinical vocal disease assessment. In order to investigate the relationship between PTF and phonatory system properties, the stability of the body-cover vocal fold model was analyzed. The study has theoretically shown that PTF is a sensitive aerodynamic parameter dependent on tissue properties, glottal configuration, and vocal tract loading. It was predicted that PTF can be reduced by decreasing tissue viscosity, decreasing mucosal wave velocity, increasing vocal fold thickness, or decreasing prephonatory glottal area. Furthermore, it was predicted that a divergent glottis or low vocal tract resistance lead to a reduced PTF. Also discussed is the potential significance of PTF in investigating the energy distribution in a vocal fold vibration system and related clinical applications.