The nasal cycle in respiratory defence.

The review describes the phenomenon of the nasal cycle, which consists of periodic congestion and decongestion of the nasal venous sinuses and an alternation of airflow from one side of the nose to the other over a period of several hours. The hypothesis is put forward that the nasal cycle may have a role in respiratory defence by; (a) alternation of the work of air conditioning between the nasal passages (b) generation of a plasma exudate which physically cleanses the epithelium and provides a source of antibodies and inflammatory mediators (c) maintaining the patency of the airway during the inflammatory response to infection.