Electromyographic activity of the stylopharyngeus muscle in exercising horses.

This study investigates how the stylopharyngeus muscle, a muscle in the throat of horses, works during exercise. The researchers aim to understand the muscle’s contribution to maintaining an open airway during inspiration and its potential role in conditions such as nasopharyngeal collapse.

Methodology

• The researchers equipped five horses with a bipolar fine wire electrode on the stylopharyngeus muscle and a pharyngeal catheter. This allowed them to measure and track the muscle’s function during exercise.
• The horses were then made to exercise on a treadmill at different intensity levels (50%, 75% and 100% of their maximum heart rate).
• While the horses were exercising, the researchers recorded electromyographic activity (electrical activity produced by skeletal muscles) of the stylopharyngeus muscle and upper airway pressures.
• Then the researchers compared the muscle activity to the horses’ breathing patterns. They quantified the muscle’s activity and compared it to the baseline activity measured during the moderate exercise intensity (HRmax50).

Results

• The study showed that the stylopharyngeus muscle remains active throughout the breathing cycle but its activity increases towards the end of expiration and early during inspiration.
• The team found a tonic activity (a steady state of muscle tension) in the stylopharyngeus muscle during the expiratory phase.
• Moreover, this tonic, peak and average electrical EMG activity of the muscle increased significantly with exercise intensity.

Conclusions

• The findings reveal that the stylopharyngeus muscle plays a significant role in the breathing process by maintaining the patency of the nasopharynx during inspiration. Its function is all the more crucial as the exercise intensity increases.
• Given these findings, the researchers proposed that a failure of this muscle’s recruitment during exercise might explain why some horses experience nasopharyngeal collapse. However, they emphasized the need for further research specifically focusing on horses affected by this disease.