Properties of the laryngeal chemoreflex in neonatal piglets

Cardiorespiratory reflex responses to laryngeal chemoreceptor stimulation were studied in 62 piglets of both sexes varying in age from 1 to 79 days. The distal trachea was cannulated to provide a free airway and the proximal end used to introduce fluids into the laryngeal area. Introduction of either water or milk produced apnea, bradycardia, and hypertension. Swab application of test fluids to the laryngeal epithelium produced similar responses. The reflex could be interrupted by flushing the laryngeal region with saline, by cutting the superior laryngeal nerves (SLN) or by anesthetizing the laryngeal epithelium with lidocaine. Electrical stimulation of SLN elicited identical responses. Respiratory inhibition by the reflex was enhanced following central depression with chloralose and overridden by administration of the respiratory stimulant, aminophylline. The relative potency of the laryngeal reflex was estimated to be equivalent to about 40% of the dose of chloralose which produced permanent respiratory arrest. It is concluded that in circumstances where respiratory drive is reduced the laryngeal inhibitory reflex is capable of caused persistent apnea and asphyxial death in the young piglet.