Relationships between vocal intensity and noninvasively obtained aerodynamic parameters in normal subjects.

The relationships between vocal intensity (sound pressure level) and intrapulmonic pressure, mean flow rate, and aerodynamic powere were investigated in ten normal subjects. The intrapulmonic pressure was measured noninvasively and simultaneously with sound pressure level and mean flow rate during sustained phonation of the vowel/a/by means of plethysmographic and pneumotachographic methods. The aerodynamic power was calculated as intrapulmonic pressure times mean flow rate. The averaged values for the normal subjects represented (sound power) alpha (intrapulmonic pressure), (sound power) alpha (mean flow rate), and (sound power) alpha (aerodynamic power), where sound power at the open end of the pneumotachograph was estimated from sound pressure level. Vocal efficiency was defined as the ratio of sound power to aerodynamic power. Individual variation of coal efficiency (in dB) was satisfactorily small in the normal subjects, and was determined by the simple addition of individual variations of intrapulmonic pressure and mean flow rate (in dB) from the averaged values. These findings strongly suggested that the comparison of those three measurements against normative data for normal subjects such as provided by this study is useful in evaluating and clarifying the ineffective voice production of the pathological larynx.