page_title: Exhaled nitric oxide
section_title: Measurement techniques
hierarchical_section_title: Exhaled nitric oxide / Measurement techniques
caption_attribution_description: English: An experimental setup used to measure the fraction of exhaled nitric oxide (FeNO) in human breath samples. The subject blows into the tube (1) after a mouthpiece (2) has been connected to it. The wires on the side measure parameters like breath velocity, while the exhaled gas is taken to a FeNO analyzer (3).
context_page_description: In medicine, exhaled nitric oxide can be measured in a breath test for asthma or other conditions characterized by airway inflammation. Nitric oxide is a gaseous molecule produced by certain cell types in an inflammatory response. The fraction of exhaled NO 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.
context_section_description: The most widely used technique to measure eNO is with a chemical reaction that produces light; this is called a chemiluminescence reaction. The NO in the breath sample reacts with ozone to form nitrogen dioxide in an excited state. When this returns to its ground state, it emits light in quantities that are proportional to the amount of exhaled NO.
  The subject can exhale directly into a measurement device ('online' technique), or into a reservoir that can afterwards be connected to the analyser ('offline' technique). With the former technique, the early and later NO in the breath sample can be analysed separately. The test requires little coordination from the subject, and children older than 4 can be tested successfully.
  The National Institute of Clinical Excellence (NICE) in the UK have published guidance on available measuring devices: https://www.nice.org.uk/guidance/dg12
caption: An experimental setup used to measure the fraction of exhaled nitric oxide (FeNO) in human breath samples. The subject blows into the tube (1) after a mouthpiece (2) has been connected to it. The wires on the side are part of the system that measures parameters like breath velocity, while the exhaled gas is taken to a FeNO analyzer (3).
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