Airway acidification: interactions with nitrogen oxides and airway inflammation.

Airway acidification is increasingly appreciated to occur in inflammatory obstructive airway diseases, resulting from acid reflux and aspiration and from direct acid formation in the airways. Acidity activates oxidants and nitrogen oxides to create a potent antimicrobial environment. Neurogenic inflammation is triggered by airway or esophageal acidification, innate immune cells are affected by acidity, and there are pathways by which the acquired immune system also can be activated by the chemistry of an acidic airway. Measuring airway acidity is now readily achievable with noninvasive breath assays, a procedure that has opened a window on the need to understand airway pH homeostasis in health and pH dysregulation in disease.