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Disordered voices are often associated with abnormal changes in aerodynamic parameters of subglottal pressure (P(s)) and airflow. Phonation instability pressure (PIP) has been previously proposed to evaluate P(s) at the onset of chaotic phonation. We propose the concept of and measure phonation instability flow (PIF), the airflow at which phonation becomes chaotic. Phonation flow range (PFR), PIF minus phonation threshold flow (PTF), is proposed to assess the range over which normal vocal fold vibration occurs.Repeated measures with each ex vivo larynx serving as its own control.Pressure and airflow were measured at phonation onset and chaos onset in seven excised canine larynges under three experimental conditions: 0% elongation with no glottal gap; 20% elongation with no glottal gap; 20% elongation with a 3-mm posterior glottal gap. Paired t tests were performed to determine if experimental measurements differed between elongations (0% and 20%) or degrees of abduction (20% elongation with and without a 3-mm glottal gap).Both PIF and PFR were dependent on abduction but not elongation. PIP was not significantly dependent on either condition. PIF and PFR showed greater differences for abduction than either phonation threshold pressure (PTP) or PTF.PIF and PFR may be useful parameters in the experimental or clinical settings, particularly when evaluating disorders characterized by a glottal gap, such as vocal fold paralysis and presbylaryngis.