Electromyographic activity of the hyoepiglotticus muscle and control of epiglottis position in horses.

This study investigates the relationship between the hyoepiglotticus muscle and the positioning of the epiglottis in horses, and whether the electrical stimulation of this muscle affects the shape and position of the epiglottis, thus altering the dimensions of the respiratory tract. The results found suggest that contraction of this muscle could help maintain an open airway during intense breathing in horses.

Article Explanation

Objective and Methodology

• The primary aim of the study was to explore whether the hyoepiglotticus muscle, a muscle in the throat of a horse, exhibits any respiratory-related electromyographic activity, and if stimulating it electronically would change the position and conformation of the epiglottis (a flap that prevents food from entering the windpipe).
• The researchers performed their experiment on six Standardbred horses, under anaesthetic conditions. They placed a bipolar fine-wire electrode in the hyoepiglotticus muscle of each horse for the electronic stimulation and recording of its electromyographic activity.
• In addition, endoscopic images were recorded to capture changes in the nasopharynx (the area above the soft part of the roof of the mouth and behind the nose) and the larynx (the organ housing the vocal cords) during this stimulation.

Measurements and Recordings

• The scientists measured the dorsoventral length and area of the aditus laryngis (the opening in the larynx) on these images, both before and during the stimulation to observe any modifications.
• Further, they measured the electromyographic activity of the hyoepiglotticus muscle and the nasopharyngeal pressures when the horses were subjected to varying speeds on a treadmill. They did this at 50, 75, 90, and 100% of the speed that produced the horse’s maximum heart rate.

Results and Conclusion

• The results showed that electrical stimulation of the hyoepiglotticus muscle not only altered the shape of the epiglottis ventrally (towards the belly) but significantly increased the size of the aditus laryngis. The muscle had increased inspiration activity that elevated significantly with treadmill speed due to a hike in both, phasic (sudden and brief) and tonic (sustained) activity.
• However, it’s worth noting that expiration activity of the muscle didn’t change with treadmill speed in four of the six horses.
• In conclusion, Findings suggest that contraction of the hyoepiglotticus muscle enhances the airway’s dimensions in horses through depressing the epiglottis ventrally during profound breathing efforts. Thus, the muscle represents a vital muscle for enlarging the airway in horses, and its contraction may induce configuration changes in the epiglottis.