Laryngeal paralysis occurs primarily in older large breed dogs, but can occur in any breed. Over time the nerve that serves to stimulate a small muscle within the larynx becomes non functional. This muscle normally acts to open the larynx at the level of the vocal chords when the dog inhales. As the nerve fails, the muscle no longer contracts when the dog inhales. As a result, the vocal chords don't spread apart and the airway is narrowed resulting in noisy obstructed respiration on the inhale. As function deteriorates further, the larynx begins to actually narrow further with the negative pressure created by stronger efforts to inhale resulting in the vocal chords closing together. The harder the dog tries to inhale, the more the larynx narrows. This situation can lead to sudden respiratory crisis, especially if the dog is challenged by heat or exertion.
Laryngeal paralysis is addressed surgically with a procedure known as unilateral arytenoid lateralization. In this procedure a permanent suture is placed on the outer surface of the larynx anchored at the same sites that the now paralyzed muscle is normally anchored. The suture is tightened and tied resulting in opening of that side of the airway. Only one side is tied back in this fashion to reduce the likelihood of aspiration of material into the airway.