High-speed treadmill endoscopy findings
All horses developed exercised-induced compression of the base of the epiglottis from the first phase of induced poll flexion (phase 2), often with exacerbation during subsequent phases of poll flexion. Compression was bilateral in 13/18 horses (72.2%) (Figure 1 and 2) and unilateral in 5/18 horses (27.8%), with equal distribution between left and right sides (Figure 3 and 4). Bilateral compression was seen in 10 of 11 NSCTs (90.9%) and in 3 of 7 STBs (42.9%), whilst unilateral compression was seen in 4 of 7 STBs and in 1 of 11 NSCTs. All horses demonstrated a unilateral or bilateral inward bulging of the nasopharyngeal wall adjacent to the compressed side of the epiglottis (green arrows in figures) during periods of exercise in poll flexion.
One horse (horse nr. 1) also developed moderate ventromedial luxation of the apices of the corniculate processes during the first phase of poll flexion after development of epiglottic compression, which persisted during phases without poll flexion. Two horses developed intermittent dorsal displacement of the soft palate (iDDSP) (horse nr. 8 and 11) at the end of the examination protocol (phase 6 and 5, respectively) when the horses were completely fatigued and could not maintain the trotting gait and position on the treadmill. This was several minutes after developing compression of the base of the epiglottis. Two additional horses developed palatal instability (horse nr. 7 and 9) and MDAF (horse nr. 12 and 13) respectively, also several minutes after the onset of epiglottic compression (phases 4-6).