Assaying all of the nitrogen oxides in breath modifies the interpretation of exhaled nitric oxide

Exhaled nitric oxide (NO) assays measure the quantity of NO that emanates from the airway, not the amount of NO that is formed. Consumptive processes-including oxidation reactions-decrease the amount of gas phase NO available for exhalation. Higher oxides of nitrogen (HiNOx) are resulting reaction products, and are easily measured in exhaled breath condensate (EBC). We performed concurrent sampling of exhaled breath for gas phase NO and EBC HiNOx in controls and stable asthmatics. We identified that, mole for mole, asthma patients hourly exhale more HiNOx than they do NO, with a HiNOx/NO ratio of 1.21 (0.54-3.4). This is the reverse of the ratio found in controls, in whom the HiNOx/NO ratio was 0.75 (0.44-0.93), p = 0.04. The sum of the hourly molar exhalation of NO and HiNOx was significantly higher in asthmatics (333 nmol/h (221-543) than controls (179 (138-231), p < 0.001). We conclude that exhaled oxides of nitrogen are more informative when measured together as opposed to in isolation. We suggest that inflammation can be better evaluated with HiNOx and NO measured concurrently, and that the level of oxidation in the lung can be evaluated by comparing the easily measured ratios of HiNOx to NO in the exhaled breath.