THE ROLE OF STRAP MUSCLES IN PHONATION - IN-VIVO CANINE LARYNGEAL MODEL

In spite of the presumed importance of the strap muscles on laryngeal valving and speech production, there is little research concerning the physiological role and the functional differences among the strap mus cles. Generally, the strap muscles have been shown to cause a decrease in the fundamental frequency (F-0) of phonation during contraction. I n this study, an in vivo canine laryngeal model was used to show the e ffects of strap muscles on the laryngeal function by measuring the F-0 , subglottic pressure, vocal intensity, vocal fold length, cricothyroi d distance, and vertical laryngeal movement. Results demonstrated that the contraction of sternohyoid and sternothyroid muscles corresponded to a rise in subglottic pressure, shortened cricothyroid distance, le ngthened vocal fold, and raised F-0 and vocal intensity. The thyrohyoi d muscle corresponded to lowered subglottic pressure, widened cricothy roid distance, shortened vocal fold, and lowered F-0 and vocal intensi ty. We postulate that the mechanism of altering F-0 and other variable s after stimulation of the strap muscles is due to the effects of lary ngotracheal pulling, upward or downward, and laryngotracheal forward b ending, by the external forces during strap muscle contraction.