INFLUENCE OF HYOEPIGLOTTICUS MUSCLE-CONTRACTION ON CANINE UPPER AIRWAY GEOMETRY

We examined the effect of hyoepiglotticus (HE) muscle contraction on e piglottic position in 4 anaesthetised (IV choralose, pentobarbitone so dium) tracheostomised, mechanically ventilated dogs studied in the pro ne mouth open position. Computerised axial tomography (coronal plane) was used to measure the vertical distance between the tip of the epigl ottis (E) and (1) the soft palate (SP) (i.e. E-SP distance) and (2) th e dorsal wall of the nasopharynx (N) (i.e. E-N distance). Duplicate ru ns of graded electrical stimulation of the HE muscle, using bilateral bipolar fine wire electrodes, were performed in each animal and result ed 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 di stance (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 fr om the soft palate thus opening and enlarging the oral pathway for air flow.