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Principal Investigator: Dr. Jon Cheetham
Mentor: Dr. Normand Ducharme
Contact Information: E-mail: ngd1@cornell.edu - Phone: 607-253-3109
Sponsor: Grayson-Jockey Club Research Foundation, Inc.
Grant Number: N/A
Title: The Role of the Tongue Muscles in Respiration in Horses
Annual Direct Cost: $14,999
Project Period: 04/01/06-03/31/07
Dorsal displacement of the soft palate (DDSP) is a common cause of upper airway obstruction and poor performance in race horses. The known causes of DDSP can be classified under intrinsic and extrinsic dysfunctions.
Intrinsic dysfunctions are seen with decreased tone in muscles of the palate. The palatinus (PT), tensor veli palatini (TVP), caudal stylopharyngeus (CSP) and hyoepiglotticus (HE) muscles have all been evaluated as candidates important in the etiology of DDSP. Extrinsic causes are related to the musculature that controls the position of the larynx and hyoid apparatus and are not fully understood. Our long term goal is to elucidate all the mechanisms controlling pharyngeal and palate respiratory function during exercise.
The specific hypothesis is that the equine genioglossus (GG) and geniohyoid (GH) muscles stabilize the laryngohyoid apparatus and nasopharynx during exercise. The respiratory role of these muscles has not been evaluated in the horse. We base this hypothesis on the observations that 1) altering the position of the laryngohyoid apparatus using an external device prevents experimentally-induced DDSP at exercise 2) the genioglossus muscle has a major role in stabilizing the upper airway in humans. 3) preliminary data suggests that the mean electrical activity of the genioglossus muscle increases as speed increases during exercise. 4) tongue-tie devices have been shown to prevent DDSP in some horses. 5) a clinical study currently underway at our hospital has demonstrated that the basihyoid bone is significantly more ventral in horses with DDSP and, 6) a pilot study suggests that ultrasound guided blockade of the hypoglossal nerve, at the level of the ceratohyoid bones, causes increased flaccidity in the palate at exercise.
Based on these observations, the experimental focus of this proposal is the respiratory role of the genioglossus and geniohyoid muscles at rest and at exercise. Specifically we will: I) Measure the relationship between GG and GH muscle EMG activity and exercise intensity 2) Establish the effect of bilateral hypoglossal nerve blockade at the level of the ceratohyoid bones on GG and GH EMG muscle activity and 3) Characterize the effect of bilateral hypoglossal nerve blockade on airway mechanics at exercise. These experiments will enable us to test our hypothesis that the GG and GH muscles have a respiratory function in the horse and stabilize the nasopharynx during exercise. This information will enhance our ability to effectively treat DDSP.
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