Background: Nitric oxide (NO) is a gaseous molecule produced by certain cell types in an inflammatory response.The Fraction of exhaled NO (FeNO) is an aspecic, non-invasivebiomarker that can be used for asthma diagnosis, follow-up andtherapy; it correlates with bronchial hyperresponsiveness and withsputum eosinophilia [Kaiser et al. 2008, Taylor et al. 2006].To measure FeNO in exhaled air, subjects are asked to inhale NOfree air deeply to total lung capacity through a lter connected to ananalyzer, and to exhale slowly through the lter for 10s.Different expiratory flow rates are ensured by placing expiratoryresistors in the exhalation circuit, which yield expiratory flow rates of 50, 100, 200 and 250 ml/s.FeNO:1. is usually modied by smoking habits and asthma2. is usually higher in atopic subjects3. is flow-dependent (higher at lower flow rates and viceversa)Measurements are normally set up at 50 ml/s, but the flow rate that better discriminates between asthmatic and non asthmatic subjects is still unknown.Aim: To test the power of different flow rates of FeNO to discriminate between asthmatic subjects and controls.Conclusion:FeNO 100: best performance.FeNO 50 and FeNO 100 have a similar validity in identifying subjects with current asthma.FeNO 100 has a statistically significant greater AUR than FeNO200 and than FeNO 250.
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