Effect of topical anesthesia of the laryngeal mucosa on upper airway mechanics in exercising horses.

The research paper investigates how desensitizing the laryngeal mucosal mechanoreceptors, using topical anesthesia, impacts upper airway mechanics in a group of Standardbreds while exercising. The results suggest that these receptors play a vital role in maintaining upper airway patency in exercising horses.

Research Methods

• The study was separated into two parts. In the first study, videoendoscopic examinations were carried out on six Standardbred horses while they ran on a treadmill. These were conducted both with and without the application of topical anesthesia to the laryngeal mucosa.
• For the second part of the study, tracheal and nasopharyngeal pressures, as well as airflows, were obtained from the animals during ongoing incremental exercise tests on the treadmill. Similar to the first study, these tests were carried out when the horses’ laryngeal mucosa was anesthetized, and when it was not.
• A nasal occlusion test was also administered to each horse while they were standing during an endoscopic examination, across both trials.

Findings

• According to the results of the first study, the horses experienced nasopharyngeal collapse while running on the treadmill when their laryngeal mucosa was anesthetized.
• The outcomes of the second study revealed that inspiratory upper airway and nasopharyngeal impedance were significantly higher, and peak tracheal inspiratory pressure, respiratory frequency, and minute ventilation were notably lower in the horses when the laryngeal mucosa was anesthetized, in comparison to when they exercised without topical anesthesia.
• Peak inspiratory and expiratory airflows were lower when the laryngeal mucosa was anesthetized, however, these differences did not quite reach significance.
• During the nasal occlusion test, the horses had episodes of nasopharyngeal collapse and dorsal displacement of the soft palate when the laryngeal mucosa was anesthetized. Normal upper airway function was observed in these horses without laryngeal mucosal anesthesia.

Conclusion

This research led to the conclusion that receptors located in the laryngeal mucosa may play a significant role in maintaining upper airway patency in exercising horses. The application of a topical anesthetic to these areas led to increased airway impedance and decreased tracheal pressure, respiratory frequency, and ventilation rate. Further investigations on the role and regulation of these laryngeal receptors could lead to improved understanding and treatment of equine respiratory disorders.