Electromyographic activity of the stylopharyngeus muscle in exercising horses.
Authors: Tessier C, Holcombe S J, Stick J A, Derksen F J, Boruta D
Journal: Equine veterinary journal
Summary
# Electromyographic activity of the stylopharyngeus muscle in exercising horses The stylopharyngeus muscle plays a critical role in maintaining nasopharyngeal patency during exercise, yet little was known about its recruitment patterns or how it responds to increasing workload—information essential for understanding why some horses experience dorsal pharyngeal collapse. Tessier and colleagues used fine-wire electromyography and pharyngeal catheterisation in five horses exercised on a treadmill at intensities corresponding to 50%, 75% and 100% of maximum heart rate, simultaneously recording muscle activity and upper airway pressures to establish the temporal relationship between stylopharyngeal function and breathing mechanics. The muscle demonstrated continuous tonic activity throughout the breathing cycle, with marked increases in peak, mean and tonic electromyographic activity as exercise intensity increased (P<0.05); critically, activity peaked early during inspiration, indicating inspiratory-phase recruitment to support airway patency during the negative pressure phase of breathing. These findings suggest that failure of the stylopharyngeus to recruit appropriately during work could predispose horses to upper airway collapse, providing a mechanistic basis for investigating disease in affected horses. For practitioners managing horses with suspected nasopharyngeal dysfunction, this research underscores the importance of considering muscle recruitment failure as a potential component of collapse, though further investigation of the stylopharyngeus in clinically affected individuals is required.
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Practical Takeaways
- •Stylopharyngeus muscle dysfunction during high-intensity exercise may underlie nasopharyngeal collapse cases; assessment of this muscle's activity could help diagnose and explain poor performance in affected horses
- •The muscle's activity increases proportionally with exercise intensity, suggesting that horses with recruitment failure will show worsening upper airway obstruction at faster speeds
- •Understanding normal stylopharyngeus function provides a baseline for investigating abnormal cases, which may lead to better diagnostic and therapeutic approaches for airway collapse
Key Findings
- •Stylopharyngeus muscle showed ongoing activity throughout the breathing cycle with activity peaking early during inspiration
- •Peak, mean electrical, and tonic EMG activity increased significantly (P<0.05) with exercise intensity from HRmax50 to 100%
- •Tonic activity was present during expiration in addition to inspiratory-related activity
- •Failure of stylopharyngeus muscle recruitment during exercise may explain clinical cases of dorsal pharyngeal collapse