Exhaled nitric oxide in asthmatic and non-asthmatic children: influence of type of allergen sensitization and exposure to tobacco smoke.

Asthmatic bronchial inflammation is associated with increased nitric oxide concentrations in exhaled air (eNO). Recent data suggest that this effect arises from atopy. Our aim in this study was to find out whether atopy and sensitization to particular allergens influences eNO levels. A total of 213 subjects (41 asthmatics and 172 controls) (96 boys and 117 girls, 7.3-14 years of age) were studied. Parents completed a questionnaire that sought information on their children's respiratory symptoms and exposure to tobacco smoke. Subjects underwent skin-prick tests for the following common allergens: Dermatophagoides pteronyssinus (Dpt), cat fur, Aspergillus fumigatus, Alternaria tenuis, mixed grass, mixed tree pollen, Parietaria officinalis, egg, and cow's milk. eNO was collected in 1-l mylar bags (exhaled pressure 10 cmH2O, flow 58 ml/s) and analyzed by using chemiluminescence. Atopic and non-atopic children without a history of chronic respiratory symptoms had a similar geometric mean eNO (atopics, n = 28, 11.2 p.p.b.; non-atopics, n = 96, 10.0 p.p.b.; mean ratio 1.1, 95% confidence interval [CI]: 0.7-1.6). Conversely, atopic asthmatic subjects had significantly higher eNO values than non-atopic asthmatic subjects (atopics, n = 25, 24.8 p.p.b.; non-atopics, n = 16, 11.4 p.p.b.; mean ratio 2.2, 95% CI: 1.2-3.9, p= 0.000). In children with rhinitis alone (n = 15) and those with lower respiratory symptoms other than asthma (n = 33), eNO increased slightly, but not significantly, with atopy. eNO levels correlated significantly with Dpt wheal size (r = 0.51) as well with the wheal size for cat, mixed grass, and Parietaria officinalis (r = 0.30-0.29), and with the sum of all wheals (r = 0.47) (p= 0.000). Subjects sensitized only for Dpt (but not those subjects sensitized only for grass pollen or other allergens) showed significantly higher eNO levels than non-atopic subjects (16.4 p.p.b. vs. 10.2 p.p.b., mean ratio 1.6, 95% CI: 1.1-2.3, p= 0.002). In asthmatic subjects, Dpt sensitization markedly increased eNO levels (Dpt-sensitized subjects: 28.0 p.p.b.; Dpt-unsensitized subjects: 12.2 p.p.b.; mean ratio 2.3, 95% CI: 1.5-3.5, p= 0.000). Non-asthmatic Dpt-sensitized subjects also had significantly higher eNO values than non-asthmatic, non-Dpt-sensitized subjects (14.2 p.p.b. vs. 10.1 p.p.b.; mean ratio 1.4, 95% CI: 1.1-1.9, p= 0.008). No difference was found between eNO levels in asthmatic subjects and control subjects exposed or unexposed to tobacco smoke. In conclusion, eNO concentrations are high in atopic asthmatic children and particularly high in atopic asthmatics who are sensitized to house-dust mite allergen.