Age dependence of laryngeal chemoreflex in puppies.

Previously collected data have indicated that the laryngeal chemoreflex (LCR) response is exaggerated during a critical period of postnatal development in several experimental animals. These animals had fewer anatomic and physiological similarities to humans than do puppies. This investigation of the LCR in 14 anesthetized puppies was undertaken to determine age-related differences in the response to stimulation of the supraglottic laryngeal mucosa by saline solution, distilled water, cow's milk, and acid at pH 1.0. The dogs were divided into 3 age groups: group 1 consisted of 4 dogs that were 2 weeks old, and in groups 2 and 3 there were 5 puppies each, of 4 and 6 weeks of age, respectively. The LCR response (laryngospasm, apnea, respiratory depression, and bradycardia) was found in the puppies only after stimulation of the laryngeal mucosa with acid at pH 1.0, and it was more easily achieved in the 4- and 6-week age groups than in the 2-week group. These findings 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 that postnatal neural maturation may influence the laryngeal reflex in humans to some extent.