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

Objective-To determine the effect of desensitization of the laryngeal mucos al mechanoreceptors on upper airway mechanics in exercising horses. Animals 6 Standardbreds. Procedure-In study 1, videoendoscopic examinations were performed while hor ses ran on a treadmill with and without topical anesthesia of the laryngeal mucosa. In study 2, peak tracheal and nasopharyngeal pressures and airflow s were obtained from horses during incremental treadmill exercise tests, wi th and without topical anesthesia of the laryngeal mucosa. A nasal occlusio n test was performed on each horse while standing during an endoscopic exam ination for both trials. Results-In study 1, horses had nasopharyngeal collapse while running on the treadmill when the laryngeal mucosa was anesthetized. In study 2, inspirat ory upper airway and nasopharyngeal impedance were significantly higher, an d peak tracheal inspiratory pressure, respiratory frequency, and minute ven tilation were significantly lower in horses when the laryngeal mucosa was a nesthetized, compared with values obtained when horses exercised without to pical anesthesia. Peak inspiratory and expiratory airflows were lower in ho rses when the laryngeal mucosa was anesthetized, although differences did n ot quite reach significance (P = 0.06 and 0.09, respectively). During a nas al occlusion test, horses had episodes of nasopharyngeal collapse and dorsa l displacement of the soft palate when the laryngeal mucosa was anesthetize d. Upper airway function was normal in these horses without laryngeal mucos al anesthesia. Conclusions and Clinical Relevance-Receptors within the laryngeal mucosa ma y be important maintaining upper airway patency in exercising horses.