The airway is a continuous structure extending from the nasal vestibule to the alveoli, with the same pseudostratified ciliated columnar epithelium along much of its length. While an arbitrary line at the level of the vocal cords divides the airway into upper and lower subdivisions—a concept introduced in medical school anatomy tutorials and continued in patient care—airways disease does not conform to such specific anatomical regions. Upper and lower airway disease often coexist, with upper airway involvement often preceding that of the lower airway and even determining severity of disease and quality of life.1 This recognition has led to the development of the terms “united airways” and “one airway, one disease”.

The nose is an air conditioner—filtering, warming and humidifying over 10 000 litres of air daily before it progresses to the lungs. The nasal passages and associated structures bear the brunt of environmental contact, being the first site of allergen, microbial and particle deposition. As a consequence, the upper airway is the location of a highly-developed innate and adaptive immune system. Effective mucociliary clearance is vital for respiratory health, as evidenced by the effects of defects such as primary ciliary dyskinesia (PCD) and cystic fibrosis. Sinus disease is almost universal in these patients, and even the subgroup of idiopathic bronchiectasis demonstrates high rates of chronic sinus infection, polyps and inflammation.2 Simple measures such as nasal douching can help with symptoms and quality of life. Measurement of nasal nitric oxide is simple and quick,3 and very low levels can alert the physician to the possibility of PCD before major lung damage is sustained, thus allowing the benefit of early physiotherapy.

An important lymphoid tissue mass (tonsils and adenoids) collectively termed Waldeyer’s ring and prominent in childhood is a unique immunological organ surrounding the upper airway. It supports development …