Influence of hyoepiglotticus muscle contraction on canine upper airway geometry.

We examined the effect of hyoepiglotticus (HE) muscle contraction on epiglottic position in 4 anaesthetised (IV choralose, pentobarbitone sodium) tracheostomised, mechanically ventilated dogs studied in the prone mouth open position. Computerised axial tomography (coronal plane) was used to measure the vertical distance between the tip of the epiglottis (E) and (1) the soft palate (SP) (i.e. E-SP distance) and (2) the dorsal wall of the nasopharynx (N) (i.e. E-N distance). Duplicate runs of graded electrical stimulation of the HE muscle, using bilateral bipolar fine wire electrodes, were performed in each animal and resulted in a progressive increase in both the E-SP distance (baseline of 0.5 +/- 0.5 to a maximum of 13.1 +/- 2.3 mm, mean +/- SE) and the E-N distance (29.1 +/- 2.0 to a maximum of 42.2 +/- 2.7 mm, both p < 0.02). We conclude that HE contraction moves the epiglottis ventrally away from the soft palate thus opening and enlarging the oral pathway for airflow.