Nitric oxide in exhaled air.

Much interest is now being focused on measurements of nitric oxide (NO) in exhaled air. In healthy subjects exhaled NO seems to originate mainly in the nasal airways, whereas the contribution from the lower respiratory tract is low. In certain inflammatory airway disorders, the excretion of NO into the airways is altered resulting in changes in the levels of NO in exhaled air. New techniques have been developed to measure NO release at different levels of the airways: asthmatics show increased orally-exhaled NO levels, whereas patients with cystic fibrosis or Kartagener's syndrome exhibit a marked reduction in nasal release of NO. It has been suggested that measurements of exhaled NO may be clinically useful in noninvasive diagnosis and monitoring of inflammatory airway diseases. To further evaluate the potential clinical usefulness of measurement of exhaled NO, it is vital to explore how airway NO production is normally regulated and what factors influence airway NO excretion.