Exhaled nitric oxide in asthmatic airway inflammation

Measuring the level of exhaled NO (eNO) in the breath is a new method tomonitor airway inflammation in asthma and may have a role in the managementof asthma. The hypotheses were that eNO will reflect the degree ofinflammation in chronic asthma, and will indicate how anti- inflammatory therapyshould be altered to improve asthma control.Three studies were performed to test the hypotheses. A cross sectional studywas performed to define the normal range of eNO and to compare this rangewith those who have asthma or atopy. The second study was observational, tocompare the level of eNO during and after an exacerbation of asthma. The thirdstudy was an interventional study to evaluate eNO in management of paediatricasthma. In this latter study the level of eNO was measured to monitor airwayinflammation in asthmatic children with the intention of adjusting antiinflammatorydrugs (inhaled glucocorticosteroids) according to the level of eNO.These studies have shown that the mean level of eNO was significantly higherin asthmatic compared with normal subjects, but not significantly different whencompared with atopic non-asthmatic subjects. eNO was correlated with thenumber of positive skin prick tests in atopic subjects whether asthmatic or nonasthmatic.The eNO level was increased during acute exacerbations of asthmaand decreased after two weeks with therapy of GCS. In a pilot study eNOappeared to be superior to FEV1 in adjusting the dose of iGCS to controlasthmatic children, but this needs to be confirmed with a larger sample size.Another non-invasive method to detect inflammatory markers is the technique ofexhaled breath condensate (EBC). Although NO is degraded to NOx, it wasfound that eNO had no significant correlation with EBC NOx but had asignificant correlation with pH.Hypertonic saline challenge, an artificial model of an asthmatic exacerbationwas associated with an increase in EBC volume and the release of histamine,implicating mast cell activation. These novel findings suggest that non-invasivemarkers can be used both for clinical and mechanistic proposes