Janus looks both ways: How do the upper and lower airways interact?

Our understanding of the relationship between the upper and lower airways has greatly increased as a consequence of epidemiologic and pharmacologic studies. A consistent body of scientific evidence supports the concept that rhinitis, rhinosinusitis and asthma may be the expression of a common inflammatory process, which manifests at different sites of the respiratory tract, at different times. This paradigm states that allergic reactions may begin at the local mucosa, but tend to propagate along the airway. Central to the allergic diathesis is the eosinophil and its interaction with the airway epithelium. The implications of the interplay between upper and lower airway are not only academic, but also important for diagnostic and therapeutic reasons. Furthermore, there is significant overlap in symptomatology and pathophysiology for childhood sleep disordered breathing (SDB) and asthma. Recent evidence supports an association between these two conditions, but causality has not been demonstrated. Regardless, it is important to recognize the overlap and evaluate for the other condition when one is present. In children with poorly controlled asthma, the presence of SDB may significantly contribute to asthma morbidity and, as such, should be actively excluded. On the other hand, clinical evaluation for asthma should be considered in children with SDB. Future robust longitudinal research is needed to explore the association between upper and lower airway diseases using objective measures in children.