ASC-226: Help! My Horse Roars! What is Laryngeal Hemiplegia?

Introduction The larynx of the horse is part of the upper airway and serves as a conduit between the pharynx and the trachea, or the wind pipe that takes inspired air to the lungs for gas exchange. The larynx is comprised of a number of cartilages that work together to allow for increased airflow during exercise and to close the trachea during swallowing to prevent foreign material and food particles entering the trachea and consequently the lungs. The larynx is also where the vocal cords are located, and is therefore where the voice originates and is an instrument for phonation. The cartilages that comprise the larynx are: cricoid, thyroid, epiglottis, and the arytenoids. During exercise, the arytenoid cartilages are held open (abduction) by the cricoarytenoideus dorsalis muscles, which are innervated by the recurrent laryngeal nerves. Various ailments can affect the different parts of the larynx of horses. Diseases of the larynx can produce airway obstruction and sometimes dysphagia. Obstructive diseases, such as laryngeal hemiplegia, often produce an abnormal respiratory noise and, most important, they limit airflow, which leads to early fatigue and poor exercise performance. For a video of a normal endoscopic examination of a horse, check out this video from Rood and Riddle Equine Hospital: https://www.youtube. com/watch?v=OLcqGW_Eo30.