Age dependence of laryngeal chemoreflex in puppies

Previously collected data have indicated that the laryngeal chemoreflex (LC R) response is exaggerated during a critical period of postnatal developmen t in several experimental animals. These animals had fewer anatomic and phy siological similarities to humans than do puppies. This investigation of th e LCR in 14 anesthetized puppies was undertaken to determine age-related di fferences in the response to stimulation of the supraglottic laryngeal muco sa by saline solution, distilled water, cow's milk, and acid at pH 1.0. The dogs were divided into 3 age groups: group I consisted of 4 dogs that were 2 weeks old, and in groups 2 and 3 there were 5 puppies each, of 4 and 6 w eeks of age, respectively. The LCR response (laryngospasm, apnea, respirato ry depression, and bradycardia) was found in the puppies only after stimula tion of the laryngeal mucosa with acid at pH 1.0, and it was more easily ac hieved in the 4- and 6-week age groups than in the 2-week group. These find ings suggest that the LCR is an age-dependent response that appears in dogs only after 2 weeks of age. The important implication of this finding is th at postnatal neural maturation may influence the laryngeal reflex in humans to some extent.