Objective—To determine the effect of desensitization
of the laryngeal mucosal mechanoreceptors on
upper airway mechanics in exercising horses.
Procedure—In study 1, videoendoscopic examinations
were performed while horses ran on a treadmill
with and without topical anesthesia of the laryngeal
mucosa. In study 2, peak tracheal and nasopharyngeal
pressures and airflows were obtained from horses
during incremental treadmill exercise tests, with
and without topical anesthesia of the laryngeal
mucosa. A nasal occlusion test was performed on
each horse while standing during an endoscopic
examination 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, inspiratory
upper airway and nasopharyngeal impedance were
significantly higher, and peak tracheal inspiratory pressure,
respiratory frequency, and minute ventilation
were significantly lower in horses when the laryngeal
mucosa was anesthetized, compared with values
obtained when horses exercised without topical
anesthesia. Peak inspiratory and expiratory airflows
were lower in horses when the laryngeal mucosa was
anesthetized, although differences did not quite reach
significance (P = 0.06 and 0.09, respectively). During
a nasal occlusion test, horses had episodes of
nasopharyngeal collapse and dorsal displacement of
the soft palate when the laryngeal mucosa was anesthetized.
Upper airway function was normal in these
horses without laryngeal mucosal anesthesia.
Conclusions and Clinical Relevance—Receptors
within the laryngeal mucosa may be important in
maintaining upper airway patency in exercising horses.
(Am J Vet Res 2001;62:1706–1710)