Dynamic obstructions of the equine upper respiratory tract. Part 1: observations during high-speed treadmill endoscopy of 600 Thoroughbred racehorses.

The research investigated the occurrence and nature of dynamic airway obstructions in Thoroughbred racehorses, particularly those experiencing poor performance, using treadmill exercise testing and video endoscopic recordings. It found that dynamic collapse of the upper respiratory tract was common and often complex, with palatal instability and dorsal displacement of the soft palate the most frequently identified disorders.

Methodology

• The study reviewed video-endoscopic recordings of the upper respiratory tracts of 600 Thoroughbred racehorses during a standardized treadmill exercise test.
• These recordings were analyzed in real time and slow motion to spot any dynamic collapses by the tissues adjacent to the pharyngeal and laryngeal airways.

Findings

• 471 out of the 600 horses exhibited dynamic collapse within the nasopharynx or larynx.
• The most frequently identified disorders were palatal instability (33%) and dorsal displacement of the soft palate (DDSP; 50%).
• The research concluded that deglutition (swallowing process) doesn’t significantly trigger DDSP.
• 30% of horses with upper respiratory tract obstructions showed complex forms of dynamic collapse where more than one structure collapses into the airway.
• The prevalence of DDSP and dynamic laryngeal collapse was significantly influenced by age. Younger horses were more prone to DDSP, while older horses were more likely to experience laryngeal collapse.
• There was no identified association with the gender or racing format of the horses.

Conclusions

• Palatal instability and DDSP were the most common forms of dynamic collapse within the upper respiratory tract of the Thoroughbred racehorses in the study. These conditions are likely indicating the same nasopharyngeal malfunction.
• Complex obstructions that involve multiple structures collapsing into the airway frequently occur, which means treatments addressing solitary disorders may often be unsuccessful.
• Younger horses were found to be more at risk of DDSP, while older horses were more vulnerable to laryngeal collapse—but not the collapse of the arytenoid cartilage itself.