Effects of stylopharyngeus muscle dysfunction on the nasopharynx in exercising horses.
Authors: Tessier C, Holcombe S J, Derksen F J, Berney C, Boruta D
Journal: Equine veterinary journal
Summary
# Editorial Summary: Stylopharyngeus Dysfunction and Nasopharyngeal Collapse in Exercising Horses Nasopharyngeal collapse during exercise remains a frustratingly common cause of poor performance and upper airway noise in horses, yet effective treatments remain elusive. Tessier and colleagues investigated the role of the stylopharyngeus muscle in maintaining a patent nasopharynx by using bilateral glossopharyngeal nerve blocks to induce muscle dysfunction whilst measuring endoscopic findings and airway pressures in horses exercised on a treadmill at three intensities (50%, 75%, and 100% of maximum heart rate). The nerve block consistently produced dorsal nasopharyngeal collapse in all subjects and significantly more negative inspiratory pressures across all exercise intensities (P = 0.0069), alongside lower respiratory frequencies (P = 0.017) compared to baseline. These findings suggest that stylopharyngeus dysfunction may be directly implicated in the clinical cases of nasopharyngeal collapse encountered in practice, though the underlying causes of spontaneous stylopharyngeal insufficiency—and how other supporting muscles contribute to airway patency—require further investigation before targeted treatments become viable. For practitioners managing racehorses, eventers and other performance animals presenting with exercise-induced upper airway obstruction, this work provides important mechanistic insight, but the immediate clinical application remains limited until diagnostic methods and interventions addressing stylopharyngeus dysfunction can be developed.
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Practical Takeaways
- •Stylopharyngeus muscle dysfunction may be a treatable cause of dorsal nasopharyngeal collapse in performance horses currently being retired for exercise intolerance
- •Clinical examination and diagnostic protocols should assess stylopharyngeal function in horses with upper airway obstruction or exercise-induced respiratory noise
- •Further research is needed to identify the etiology of stylopharyngeus dysfunction before specific treatments can be developed for affected horses
Key Findings
- •Bilateral glossopharyngeal nerve block induced stylopharyngeus muscle dysfunction and dorsal nasopharyngeal collapse in all tested horses
- •Peak inspiratory upper airway pressure was significantly more negative at all exercise speeds with stylopharyngeus dysfunction (P = 0.0069)
- •Respiratory frequency was significantly lower in horses with induced muscle dysfunction compared to controls (P = 0.017)
- •Stylopharyngeus muscle appears to function as an important nasopharyngeal dilator in horses during exercise