Measuring exhaled nitric oxide: not only a matter of how – but also why – should we do it?

The biological functions of nitric oxide are so diverseand complex that it is now becoming increasingly difficultto delineate briefly the physiological roles and pathophys-iological implications of this seemingly simple messengermolecule [1]. In respiratory medicine, NO can either beviewed as a paracrine factor (derived from endothelium,epithelium, nerves, inflammatory cells,