Pharyngeal dilation associated with cricothyroid muscle contraction in dogs.

The mechanical function of phasic respiratory-related activity of the cricothyroid muscle of the larynx is poorly understood. We studied five adult cross-bred dogs (weight 14-20 kg) deeply anesthetized with pentobarbitone sodium, mechanically ventilated via a tracheostomy, and placed prone with the mouth open. Bilateral cricothyroid muscle contraction was induced by supramaximal electrical stimulation of the external branches of the superior laryngeal nerve. Computerized axial tomography was used to assess effects of cricothyroid muscle contraction. During cricothyroid muscle contraction, oropharyngeal (tip of epiglottis) cross-sectional area increased by 18.0 +/- 3.0% (SE) (P = 0.008), whereas combined left and right piriform recess cross-sectional area increased by 85 +/- 25% (n = 4; P = 0.02) at the midepiglottic level and by 152 +/- 37% (P = 0.01) at the base of the epiglottis. Furthermore, at the base of the epiglottis the maximum horizontal distance between the alae of the thyroid cartilage increased by 21 +/- 8% (P = 0.05). In contrast, lateral glottic diameter decreased by 52 +/- 2% (n = 4; P = 0.01), whereas dorsoventral glottic diameter increased by 18 +/- 5% (n = 4; P less than 0.02). The cricothyroid muscle, therefore, has the capacity to act simultaneously as a pharyngeal dilator and a glottic constrictor and thus may play a role in the control of oropharyngeal as well as laryngeal patency.