What are measurement procedures for obtaining fractional exhaled nitric oxide (FENO) in pulmonary function testing?

Updated: May 14, 2020
  • Author: Kevin McCarthy, RPFT; Chief Editor: Nader Kamangar, MD, FACP, FCCP, FCCM  more...
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FENO measurements have been shown to be increased by nitrate-containing foods such as lettuce and may be transiently lowered by drinking coffee or water and smoking cigarettes. Patients should refrain from smoking and the ingestion of food or beverages for 1 hour before FENO measurement. Upper and lower respiratory tract viral infections may lead to increased levels of FENO, and measurement should be deferred until recovery, if possible.

Clinical instruments for the measurement of exhaled nitric oxide typically require that the patient inhale fully through the device so that ambient nitric oxide can be scrubbed. The patient then exhales into the device, which affords greater than 5 cm water resistance to assist with velum closure, thereby preventing or minimizing nasal contribution to the exhaled gas sample (nasal nitric oxide is much higher than lower airway nitric oxide). The measuring device provides auditory and visual feedback to assist with maintaining a constant exhaled flow.  A single sample deemed acceptable by the measuring device is sufficient.

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