Effects of vocal tract on aerodynamics of hemilarynx

Pressure-flow relationship was examined in the excised canine and human larynges with and without vocal tract. Canine and human larynges were prepared and cut in the midsaggital plane from the top to about 10 mm below the vocal folds. The right half was removed and replaced with a Plexiglas plate with imbedded pressure taps along the medial surface. The thyroid cartilage was glued to the plate and the arytenoid was pressed against the plate with a two-pronged probe for adduction control. The vocal tract was simulated with a 15-cm plastic tube of 25-mm diameter. Simultaneous recordings were made of the glottal pressure, mean subglottal pressure, and average airflow at various levels of adduction. Glottal adduction was controlled mechanically by inserting shims of various sizes. Oscillation was generated by the flow of heated and humidified air through the glottis. Preliminary data indicate that the pressure-flow relationships are similar to those of full larynx and are almost linear. The addition of the vocal tract increased the glottal resistance by moving these pressure-flow lines to the lower flow and higher-pressure region. The human larynx appears to phonate easier on the bench and has lower phonation threshold pressure. [Work supported by NIDCD grant DC03566.]