'Asthma is a chronic inflammatory disorder of the airways in which many cells and cellular elements play a role, in particular: mast cells, eosinophils, T lymphocytes, macrophages, neutrophils and epithelial cells. In susceptible individuals, this inflammation causes recurrent episodes of wheezing, breathlessness, chest tightness, and coughing, particularly at night or in the early morning. These episodes are usually associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment. The inflammation also causes an associated increase in the existing bronchial hyper responsiveness to a variety of stimuli.'
Basics on exhaled Nitric Oxide
Nitric oxide (NO) is an important endogenous messenger that is widespread in the human body, functioning for example, to regulate peripheral blood flow, platelet function, immune reactions, and neurotransmission, and also to mediate inflammation. In biologic tissues, nitric oxide is unstable, limiting measurement. However, in the gas phase nitric oxide is fairly stable, permitting its measurement in exhaled air. Of greatest clinical interest is the role of NO as an inflammatory mediator, particularly in asthma. For example, the National Heart, Lung, and Blood Institute, in its clinical guidelines regarding the management of asthma, offers the following definition 1: