Effect of sternothyrohyoid myectomy on upper airway mechanics in normal horses.

This research looks into the effects that the severing of two specific muscles, the sternothyroideus and sternohyoideus, has on the functioning of the upper airway in healthy horses. It was found that two weeks after this procedure, upper airway pressures and resistances significantly increased, suggesting that these muscles play a crucial role in maintaining proper airflow.

Methodology of the Study

• The study was performed on six Standardbred horses. These horses were monitored at rest and during exercises, before the surgery, 24 hours after the surgery, and two weeks post-operation.
• To measure the various pressures and flows within the horses’ upper airway, transnasal tubes known as catheters were connected to devices referred to as differential pressure transducers. A device called a pneumotachograph was attached to an airtight face mask to measure airflow.
• The horses were made to run on a treadmill to reach 50%, 75%, and 100% of their maximum consumption of oxygen. This way, the researchers could observe changes under various exercise intensities.

Findings of the Study

• At the 24-hour post-surgery check-up, the researchers found no significant difference in the horses’ airway pressure, airflow, and frequency of respiration when compared to pre-surgery measurements. This indicated that the initial impact of the surgery on the horses’ airway functions was negligible.
• However, two weeks after the surgery, there was a notable increase in the horses’ upper airway pressure and resistance during inhalation. The muscles that were severed, namely the sternothyroideus and sternohyoideus, are located in the throat area, and the observed changes underscored the fact that these muscles were critical in maintaining normal airflow.

Implications of the Study

• The findings of this study highlight the importance of the sternothyroideus and sternohyoideus muscles in ensuring the patency and stability of a horse’s upper airway. The high reliance on the capacity of these muscles to enable normal functioning and air exchange becomes even more evident when the horse is subjected to high-intensity exercises.
• Such studies can play a major role in veterinary medicine, particularly helping with decisions related to surgical interventions in the upper airway region. By emphasizing the role of specific muscles, the study enables a more informed understanding of the potential impacts and risks associated with their removal or damage.