Postnatal development of laryngeal reflexes in the dog.

An investigation of laryngeal reflex maturation was undertaken in the dog to identify its period of most rapid postnatal differentiation. The canine model was selected because of its laryngeal reflex similarity to that of the human being. Observations in the dog indicate maximum differentiation to occur 1 to 1 1/2 months postnatally, based on measurements of recurrent laryngeal nerve myelination and conduction velocity. Latency and threshold analyses of evoked laryngeal responses additionally confirm this viewpoint. The importance of these observations rests in an understanding of developmental upper respiratory tract mechanisms that may be chronologically related to causes of fatal ventilatory events producing unexplained infant death. Such a correlation, requiring further confirmation, is based on the assumption that a critical period of most rapid development allows a transient susceptibility to noxious influences that can cause a disruption in organ function and even death of that organism itself.