Study of vibratory pattern of the vocal folds in the excised canine larynx.

The effect of simulated thyroarytenoid and cricothyroid muscle contraction on the vibratory pattern of the vocal folds was studied in the excised canine larynx. To simulate the action of the thyroarytenoid muscle, small balloons were inflated in the paraglottic space at the level of the vocal folds. To simulate the action of the cricothyroid muscle, longitudinal tension was applied to the anterior commissure of the vocal folds. The photoglottographic and electroglottographic signals, sound intensity, and airflow rate were measured. This study showed that balloon inflation simulating thyroarytenoid muscle contraction produced an elevation of frequency of vibration with a decrease in open quotient, and that an increase in longitudinal tension simulating cricothyroid muscle contraction produced an elevation of frequency with an increase in open quotient. Vocal resistance decreased with increasing open quotient, amplitude of the photoglottographic waveform, and the frequency of vibration. Vocal efficiency increased with increasing photoglottographic amplitude and decreased with increasing frequency. The vocal efficiency peaked when the open quotient was approximately 0.5. This study suggests that glottographic parameters may be useful in assessing the effect of intrinsic laryngeal muscle activity on vocal efficiency and glottic resistance.