Modulations in respiratory and laryngeal activity associated with changes in vocal intensity during speech

We tested the hypothesis that different strategies are used to alter tracheal pressure (P-t) during sustained and transient increases in intensity It has been suggested that the respiratory system plays the primary role in P-t changes associated with alteration in overall intensity whereas laryngeal adjustment is primary for transient change in P-t related to emphasis. Tracheal pressure, obtained via tracheal puncture, airflow (U), and laryngeal electromyography from the thyroarytenoid muscle (TA EMG) were collected From 6 subjects during sentence production at different intensity levels and with various stress patterns. Using a technique described in a previous study, we computed lower airway resistance (R-low) from measures of P-t and U obtained during a sudden change in upper airway resistance. We used this resistance valve, together with direct measures of P-t and U during speech, to derive a time-varying measure of alveolar pressure (P-a), the pressure created by respiratory muscle activity and elastic recoil Of the lungs. P-a provided a measure of respiratory drive that was unaffected by laryngeal activity laryngeal airway resistance (R-lx) and TA EMG provided measures of laryngeal activity The results of this study indicated that, contrary to the outcome predicted by the hypothesis, there was no difference in the strategies used to alter P-t during sustained and transient increases in intensity. Although changes in both P-a and R-lx contributed to increase in P-t, the contribution of P-a was substantially greater On average, P-a contributed to 94% and R-lx to 6% of the increase in P-t associated with vocal intensity A secondary purpose of the study was to determine the extent to which laryngeal muscle activity was related to R-lx during speech. We found TA EMG activity increased with intensity but was not well correlated with R-lx, suggesting that when it contracts, the TA muscle may effect intensity by loosening the cover, which allows for greater amplitude of vocal fold vibration, without necessarily increasing laryngeal airway resistance.