Complex dynamic upper airway collapse: associations between abnormalities in 99 harness racehorses with one or more dynamic disorders.
Authors: Strand E, Skjerve E
Journal: Equine veterinary journal
Summary
# Editorial Summary: Complex Dynamic Upper Airway Collapse in Harness Racehorses Standardbred and Coldblooded trotters frequently present with multiple simultaneous upper airway disorders during exercise, yet the relationships between these conditions remain poorly understood. Strand and Skjerve examined high-speed treadmill videoendoscopy recordings from 99 harness racehorses with dynamic upper respiratory tract abnormalities, classifying eight types of collapse (including laryngeal collapse, aryepiglottic fold deviation, soft palate displacement, and epiglottic instability) and using cluster analysis to identify statistical associations between diagnoses. Complex collapse affecting more than one structure occurred in nearly 70% of cases, with axial deviation of the aryepiglottic folds showing particularly strong correlations with both palatal instability and epiglottic flaccidity (P<0.0001), whilst dynamic laryngeal collapse associated with poll flexion linked significantly to epiglottic abnormalities (P=0.002). Rather than reflecting a generalised neurological defect, these associations appear mechanistically linked—local anatomical weaknesses in one structure creating altered airflow dynamics that destabilise adjacent tissues through Bernoulli pressure effects. For practitioners, this finding suggests that dynamic upper airway disorders should be evaluated as interconnected structural problems; treating isolated abnormalities whilst overlooking related collapse patterns may explain variable surgical outcomes and recurrent clinical signs in performance horses.
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Practical Takeaways
- •Harness racehorses presenting with upper airway dysfunction often have multiple concurrent dynamic collapse abnormalities (70% in this study), requiring comprehensive endoscopic evaluation of all URT structures rather than focusing on single suspected lesions
- •Palatal instability appears to be a key driver of secondary collapse in other URT structures; identifying and addressing PI may help prevent or reduce associated dynamic abnormalities
- •The associations between dynamic diagnoses follow anatomic/functional relationships (Bernouilli principle effects) rather than indicating a primary neurological problem, suggesting treatment approaches should focus on local structural support rather than systemic neurological intervention
Key Findings
- •Complex dynamic upper airway collapse occurred in 69.7% of harness racehorses with one or more dynamic URT disorders
- •Axial deviation of aryepiglottic folds showed significant associations with palatal instability (P<0.0001) and flaccid epiglottis (P<0.0001)
- •Caudal palatal instability appears to create two distinct pathological pathways: one leading to aryepiglottic fold deviation and another to intermittent dorsal soft palate displacement
- •Dynamic epiglottic margin collapse was commonly observed and strongly associated with laryngeal collapse, palatal instability, and aryepiglottic fold deviation, suggesting local anatomic weakness rather than generalized neurological disorder