EFFECTS OF BILATERAL HYPOGLOSSAL AND GLOSSOPHARYNGEAL NERVE BLOCKS ONEPIGLOTTIC AND SOFT PALATE POSITION IN EXERCISING HORSES

Objective-To determine the effect of bilateral hypoglossal and glossop haryngeal nerve block on epiglottic and soft palate position and trach eal and pharyngeal pressures in exercising horses. Animals-5 Standardb reds. Procedure-Tracheal and pharyngeal pressures were measured in 5 S tandardbreds exercising at the speed at which the horses achieved 50, 75, and 100% of maximal heart rate after bilateral hypoglossal and glo ssopharyngeal nerve block and without nerve block. Nerve block was ach ieved by injection of 1 to 2 mi of 2% mepivicaine hydrochloride betwee n the glossopharyngeal and hypoglossal nerves, as they coursed through the medial compartment of the diverticulum of the auditory tube (gutt ural pouch), using videoendoscopic guidance and an injection apparatus . Results-Compared with control values, peak inspiratory tracheal pres sure was significantly (P = 0.02) more negative, and peak pharyngeal i nspiratory pressure was less negative (P = 0.004) after bilateral hypo glossal and glossopharyngeal nerve block. Respiratory frequency was si gnificantly (P = 0.024) lower after nerve block, compared with control values. The epiglottis was unstable and retroflexed through the rima glottis during inspiration after bilateral hypoglossal and glossophary ngeal nerve block. Despite loss of contact between the epiglottis and the caudal free margin of the soft palate, dorsal displacement of the soft palate did not occur. Conclusions and Clinical Relevance-Loss of contact of the epiglottis with the soft palate did not affect soft pal ate position, suggesting that when the soft palate is normal, the epig lottis does not function as a support, holding the soft palate in a ve ntral position. Therefore, epiglottic dysfunction is not solely respon sible for intermittent dorsal displacement of the soft palate in horse s, and neuromuscular dysfunction involving the hyoepiglotticus muscle, geniohyoideus muscle, or the hypoglossal nerve may cause epiglottic r etroflexion in horses.