Glottal adjustment for regulating vocal intensity. An experimental study.

Living canine larynx was insufflated from the transected trachea with and without contractions of the lateral cricoarytenoid, cricothyroid and thyroarytenoid muscles, in order to study the control mechanism of vocal intensity at the glottal level. The contractions of the lateral cricoarytenoid and cricothyroid muscles were simulated with mechanical retraction, while the thyroarytenoid muscle was contracted with electrical stimulation. The vocal intensity (SPL), subglottal pressure and mean flow rate were measured simultaneously, and the aerodynamic power (pressure multiplied by flow rate) and the glottal resistance (pressure divided by flow rate) were calculated. At the same aerodynamic power, both the vocal intensity and resistance were increased by cordal adduction with contraction of the lateral cricoarytenoid muscle, whereas the vocal intensity was kept constant with contraction of the thyroarytenoid muscle in spite of increasing the resistance. Contraction of the cricothyroid muscle was inferred to influence the vocal intensity indirectly by altering the cordal adduction.