When you exhale, one of the gases you release through your airway is nitric oxide. If you produce an abnormal amount of nitric oxide, it means that your airway is inflamed. Exhaled nitric oxide is a convenient, non-invasive test that measures the quantity of nitric oxide you respire. All you have to do is bite a specialized mouthpiece and slowly exhale several times. The exhaled nitric oxide machine will analyze these exhalations and compute a composite analysis.