Exhaled nitric oxide and its relationship to airway responsiveness and atopy in asthma

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Exhaled nitric oxide (NO) has attracted increasing interest as a non-invasive marker of airway inflammation. The purpose of this study was to determine whether exhaled nitric oxide in subjects with asthma varied according to their atopic status and to examine its correlation with airway hyperresponsiveness and lung function measurements. Forty patients with asthma and 13 controls participated in the study. Nitric oxide was measured on three occasions with intervals of at least 3 days, using a chemiluminescence method. Airway responsiveness was assessed with methacholine challenge and lung function measurements were made. All subjects recorded peak expiratory flow and kept a symptom diary during a 17-day period. There was no significant difference in lung function measurements, peak expiratory flow or symptom score between the two asthma groups. Atopic patients with asthma had a significantly higher mean amount of exhaled NO than non-atopic subjects with asthma (162 ± 68 vs. 113 ± 55 nl min −1; P = 0·03) and the control group (88 ± 52 nl min −1; P = 0·004). No significant difference was found in the amount of exhaled NO between non-atopic patients with asthma and the controls. In atopic subjects with asthma the mean exhaled NO was significantly correlated to the dose-response slope for methacholine ( r = −0·52; P = 0·02), while no such correlation was found in the non-atopic group. In conclusion; in this study, atopic subjects with asthma had higher levels of exhaled NO than non-atopic subjects. Atopic status should be taken into account when measuring levels of exhaled NO in subjects with asthma.