Effects of cooling on laryngeal reflexes in the dog.

We investigated the reflex effects of laryngeal cooling on posterior cricoarytenoid (PCA) muscle activity, breathing pattern, arterial blood pressure and heart rate. We performed experiments on 9 anesthetized, spontaneously breathing dogs. Laryngeal temperature was decreased by passing cold air through the functionally isolated larynx while the dog was breathing through a tracheostomy. Inspiratory and expiratory durations, esophageal pressure, peak PCA activity, heart rate and blood pressure did not change significantly during laryngeal cooling. Upon interruption of cold airflow, while the laryngeal temperature was returning to control values, we assessed PCA response to upper airway occlusion. At laryngeal temperatures of 20-25 degrees C the peak PCA activity during upper airway occlusion was approximately 2/3 of that observed at control temperature (approximately equal to 33 degrees C). This difference was abolished by topically applied anesthetics or by superior laryngeal nerve section. In addition, we recorded from 4 laryngeal mechanoreceptors stimulated by negative pressure; their response to upper airway occlusion was reduced to 1/2 by laryngeal cooling. These results indicate that laryngeal cooling has a marked depressive effect on the PCA response to collapsing pressure in the larynx, thereby compromising the mechanism subserving upper airway patency.