Traditionally, contact between the free border of the soft palate and the ventral surface of the epiglottis was regarded as the main mechanism which stopped the soft palate from displacing dorsally to the epiglottis during breathing exercise. Dorsal displacement of the soft palate (DDSP) will of course cause varying degrees of airways compromise leading to reduced athletic performance.

We now understand that the epiglottis is actually a secondary mechanism whilst the primary process involves the formation of an oropharyngeal seal. (see A below)

Once the OPS is broken the palate moves dorsally from the floor of the oropharynx and becomes unstable but dose not necessarily displace dorsal or above the epiglottis. Bristol university researchers referred to this as ‘palatal instability’ or (PI ). (see B below) Prior to PI air cannot enter the airway via the mouth or oral route. Once PI is evident then air can move through the mouth past the intrapharyngeal ostium and into the airway. This occurs during inspiration only. If PI progresses to DDSP then air can pass though the mouth during inspiration and expiration.



References:


Lane J G et al.   Dynamic obstructions of the equine upper respiratory tract. Part 1: Observations during high-speed treadmill endoscopy of 600 Thoroughbred racehorses .  

      Equine vet. J. (2006) 38(5) 393-399


Lane J G et al.   Dynamic obstructions of the equine upper respiratory tract. Part 2: comparison of endoscopic findings at rest and during high-speed treadmill exercise of 60 Thoroughbred racehorses.    

      Equine vet. J. (2006) 38(5) 401-407.


Ahern T J.      Pharyngeal dysfunction during exercise,  including Disruption of  the Oropharyngeal Seal (OPS)  and Dorsal Displacement of the Soft Palate (DDSP).  

       J .of Eq. Vet .Sci. (1999)19.(4) 226 -  231.



DIAGRAMS A & B

(click here)


Oro Pharyngeal Seal (OPS)