Can a discrete time‐frame for change in aerodigestive tract anatomy and function in human infants be identified?

The human aerodigestive tract (ADT) is the crossroads of breathing, swallowing, and vocalizing, yet precise data on when anatomic and physiologic changes occur is poorly understood. A central determiner of ADT function is laryngeal position, which until the second year is intranarial, allowing near simultaneous breathing and swallowing. While infants have been called “obligate” nose breathers, oral tidal respiration is evidenced by transient larynx/nasopharynx unlocking by the third month and even earlier. ADT development is hypothesized to be associated with clinicopathologies reflecting developmental errors. Tracking these changes may determine if a circumscribed time period in infancy exists during which structural changes in ADT development can be found consistently to occur. This project reviewed the literature of three documented infant ADT related clinicopathologies (sleep apneas, SIDS, excessive crying) to see if any nexus in occurrence frequency could be identified. In large scale trials, these three disorders were found to show a peak incidence between 2–4 months and dramatically decreased by 6 months. These data indicate that the critical period of infant ADT development may lie between 2–4 months. Whether these changes are functional, anatomical, or both remain unclear.