Kimberly Fisher
Univ. of Oklahoma Health Sci. Ctr., 825 N.E. 14th St., Oklahoma City, OK 73190
Phonation threshold pressure (PTP) is the minimum subglottal pressure required to initiate vocal fold oscillation. This pressure is important both theoretically and clinically because of its relationship to tissue viscosity, time varying glottal flow, and vocal tract acoustics. The effects of several different measurement methods on estimated PTP were studied in normal subjects. Oral pressures during quietly voiced consonant--vowel--consonant syllable strings were used to estimate PTP. Factors expected to impact PTP estimates included: (1) low nasal flows associated with soft, relaxed phonation, and (2) vowel context, due to possible reactive loading. A significant percentage of normal subjects evidenced low, inconsistent nasal airflow during /p/ occlusion near threshold (as indicated by nasal pneumotachography). Nasal flow was not associated with supra-threshold production for these same subjects. In spite of similar instruction and pre-recording practice, subjects varied in the strategies they used to accomplish phonation at soft levels near their threshold pressure. Strategies potentially involving slight adjustment in glottal adduction were observed and would be predicted to alter PTP. These methodological challenges will be discussed relative to the variability observed in PTP estimates, and the potential impact on validity and reliability of noninvasive oral pressure measurement.