The effect of cricothyroid muscle action on the relation between subglottal pressure and fundamental frequency in an in vivo canine model

The relation between subglottal pressure (P-s) and fundamental frequency (F-0) in phonation was investigated with an in vivo canine model. Direct muscle stimulation was used in addition to brain stimulation. This allowed the P-s-F-0 slope to be quantified in terms of cricothyroid muscle activity. Results showed that, for ranges of 0-2 mA constant current stimulation of the cricothyroid muscle, the P-s-F-0 slope ranged from 10 Hz/kPa to 60 Hz/kPa. These results were compared to similar slopes obtained in a previous study on excised larynges in which the vocal fold length was varied instead of cricothyroid activation. A physical interpretation of the P-s-F-0 slope is that the amplitude-to-length ratio of the vocal folds decreases with CT activity, resulting in a smaller time-varying stiffness. In other words, there is less dependence of F-0 on amplitude of vibration when the vocal folds are long instead of short.