Complex dynamic upper airway collapse: associations between abnormalities in 99 harness racehorses with one or more dynamic disorders.

The researchers conducted a study to identify the frequency of complex dynamic upper respiratory tract (URT) collapse in harness racehorses and to explore possible associations between certain disorders. They discovered that complex dynamic URT collapse was common and that certain dynamic abnormalities were strongly associated with specific disorders.

Research Methodology

• The researchers conducted a retrospective study on 99 Standardbreds and Coldblooded trotters which had one or more dynamic Upper Respiratory Tract disorders diagnosed during high-speed treadmill videoendoscopy (HSTV).
• This technique helps in examining the functioning of the horse’s respiratory tract during exercise. The study incorporated different periods of free head carriage and poll flexion (bending of the head towards the neck) until the horses were fully fatigued.
• They classified the identified dynamic abnormalities into multiple categories, which included dynamic laryngeal collapse (DLC) associated with poll flexion, axial deviation of the aryepiglottic folds (ADAF), dynamically flaccid epiglottis (FE), caudal palatal instability (PI), intermittent dorsal displacement of the soft palate (iDDSP), pharyngeal collapse (PC), alar fold collapse (AFC), and nasal flutter (NF).
• To find associations between these disorders, they used cluster analysis and Fisher’s exact test. A significance level of less than 0.05 was set.

Findings

• The researchers identified that the overall incidence of complex dynamic URT collapse was 69.7% among the researched horses.
• They found a significant association between ADAF and PI, and between ADAF and FE. Similarly, PI was significantly associated with iDDSP. DLC associated with poll flexion had a significant relationship with FE.
• Caudal PI led to two diagnosis groupings, one of which resulted in ADAF and the other in iDDSP.

Conclusions

• The research identified that the dynamic collapse of the margins of the epiglottis was a common finding and it was strongly associated with DLC, PI, and ADAF.
• The association between certain dynamic diagnoses seemed to be because of local anatomical and functional weaknesses, which impacted other structures through the application of the Bernoulli principle.
• The Bernoulli principle explains how the pressure within a stream of fluid (in this case, air in the upper respiratory tract) decreases as its speed increase. This principle could cause negative pressure in certain areas of the respiratory tract, leading to collapse.
• The researchers suggested that these findings indicate localized weaknesses in structures of the respiratory tract rather than a generalized neurological disorder as the cause of these described dynamic conditions.