Practica oto-rhino-laryngologica. Suppl.

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The regulation of vocal intensity was studied by measuring the aerodynamic parameters in normal subjects and insuflating the living canine larynx during contractions of the intralaryngeal muscles. Among the aerodynamic parameters, such as flow rate and subglottal pressure, aerodynamic power (pressure multiplied by flow rate) was most closely related to vocal intensity. This result indicates the importance of vocal efficiency (ratio of vocal intensity to aerodynamic power) in voice production. Both the vocal efficiency and the glottal resistance (pressure divided by flow rate) were increased by cordal adduction with contraction of the lateral cricoarytenoid muscle, whereas the efficiency remained constant with contraction of the thyroarytenoid mus-cle in spite of increasing resistance. This result suggests that the thyroarytenoid muscle functions to diminish the variation of the efficiency in normal phonation.
The deviation of vocal efficiency from the normal values was investigated in patients with laryngeal disease. The efficiencies were generally abnormally low in the types of laryngeal lesions studied. An a erodynamic-biomechanical classification of laryngeal disease was inferred from the data: (1) large glottal chink, associated with high flow rate, (2) mass on vocal cord, associated with high values of both flow rate and subglottal pressure, and (3) high stiffness of vocal cord, associated with high value of subglottal pressure.
In 84 patients with voice disorders, flow rates were measured at low and high voice intensities. In cases of high stiffness of the vocal cords such as laryngeal cancer and laryngitis, the flow rate tended to be abnormally high at a high voice intensity and normal at a low intensity. This result was inferred to be influenced by high subglottal pressure in patients with very stiff cords. As a clinical examination of phonatory function, the measurement of flow rate at different voice intensities appears to be more useful than the simple measurement of flow rate during phonation.

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