FIGURE LEGENDS
Figure 1: Endoscopy image of horse nr. 3, a 3-year-old Norwegian-Swedish Coldblooded Trotter (stallion) during phase 1 (A/left) with free head carriage and during phase 4 (B/right) with induced poll flexion demonstrating compression of the base of the epiglottis (yellow arrows) along with inward deviation of the left nasopharyngeal wall (green arrow).
Figure 2: Horse nr. 18, a 5-year-old Standardbred (mare) demonstrating bilateral compression of the base of the epiglottis (yellow arrows) during phase 2; the first phase of induced poll flexion (A). The epiglottic compression is accompanied by simultaneous inward deviation of the nasopharyngeal walls (green arrow). Once relieving rein tension and reducing the angle of poll flexion, epiglottic conformation returns to normal as seen in phase 3 (B). Note the transtracheal pressure sensor passed through a polyethylene catheter for simultaneously measuring tracheal pressures.
Figure 3: Horse nr. 15, a 3-year-old Standardbred (stallion) with a normally appearing epiglottis during phase 1 (A) and unilateral compression of the left side of the base of the epiglottis (yellow arrow) with inward deviation of the left nasopharyngeal wall (green arrow) (B) during poll flexion in phase 2. Note the transtracheal pressure sensor passed through a polyethylene catheter for simultaneously measuring tracheal pressures.
Figure 4: Horse nr 4, a 4-year-old Standardbred (mare) in phase 1 (A) with a normal conformation of the epiglottis, and during poll flexion in phase 2 (B) with left sided compression of the base of the epiglottis (yellow arrow) and inward deviation of the left nasopharyngeal wall (green arrow).
Figure 5: An equine larynx/hyoid specimen illustrating the thyrohyoid articulations (red arrows top picture and bottom left) and how manual pressure applied ca. 1 cm distal to the thyrohyoid articulation causes compression of the base of the epiglottis (bottom right). Note how the vocal folds are visually obscured during epiglottic compression (bottom right).