Exhaled nitric oxide

In medicine, exhaled nitric oxide (eNO - now commonly known as FeNO) can be measured in a breath test for asthma and other respiratory conditions characterized by airway inflammation.

The fraction of exhaled NO (FENO) is a promising biomarker for the diagnosis, follow-up and as a guide to therapy in adults and children with asthma.

The breath test has recently become available in many well-equipped hospitals in developed countries, although its exact role remains unclear.

In conditions that trigger inflammation such as upper respiratory tract infections or the inhalation of allergens or plicatic acid, eNO levels rise.

Early findings indicate a possible role for eNO in predicting the response to inhaled glucocorticoids and the degree of airway obstruction reversibility.

In subjects with bronchiectasis (a state of localized, irreversible dilatation of part of the bronchial tree) not due to cystic fibrosis, high levels have been found.

In the latter condition, inhaled NO is used as a diagnostic test of the response of the pulmonary arteries to vasodilators (agents that relax the blood vessels).

[28][29] The National Institute of Clinical Excellence (NICE) in the UK have published guidance on available measuring devices: https://www.nice.org.uk/guidance/dg12 The upper normal level of eNO in different studies ranges from 20 to 30 parts per billion.

[17] Until the 1980s, nitric oxide, a product of fossil fuel combustion, was thought only to play a role the detrimental effects of air pollution on the respiratory tract.

[17] In 1987, experiments with coronary arteries showed that nitric oxide was the long sought endothelium-derived relaxing factor.

[35] Today, NO is not only used in breath tests but also as a therapeutic agent for conditions such as pulmonary arterial hypertension and possibly for the acute respiratory distress syndrome.