Preventing Airway Obstruction

During periods of intense exercise, portions of the upper airway can collapse, interfering with breathing. The cause of these obstructive episodes, most notably dorsal displacement of the soft palate (DDSP), is yet unknown. In other species, receptors in the upper airway stimulate surrounding muscles to contract, dilating and stabilizing the airway during exercise and preventing collapse. These receptors are concentrated in the mucosal lining of the larynx, and they trigger muscle contraction through a branch of the vagus nerve. If this branch is severed, these protective reflexes are greatly reduced or eliminated.

Michigan State University researchers investigated the role of laryngeal mucosal receptors in preventing airway obstruction in horses. They temporarily blocked the nerve branch to see if the incidence of airway obstruction increased. Topical anesthetic was sprayed over the larynx in six Standardbreds, which were then examined during exercise. Ten days later, they were re-examined without the topical anesthetic.

During exercise, areas of the nasopharynx in front of the larynx collapsed more often in anesthetized horses. Two horses had a collapsed nasopharyngeal roof, and two had complete collapse and obstruction. When researchers blocked the horses' nostrils, two experienced DDSP, and three suffered complete nasopharyngeal collapse. None of these abnormalities were noted during exercise without anesthetic.

Thus, airway obstruction in exercising horses is likely related to dysfunction of laryngeal receptors and/or the innervating branch of the vagus nerve.

Holcombe, S.J.; Derksen, F.J.; Berney, C; et al. American Journal of Veterinary Research, 62(11):1706-1710, 2001.

About the Author

Susan Piscopo, DVM, PhD

Susan Piscopo, DVM, PhD, is a free-lance writer in the biomedical sciences. She practiced veterinary medicine in North Carolina before accepting a fellowship to pursue a PhD in physiology at North Carolina State University. She lives in northern New Jersey with her husband and two sons.

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