The link between exhaled NO and bronchomotor tone depends on the dose of inhaled steroid in asthma

SummaryBackgroundExhaled NO (FENO) is a steroid dose dependent eosinophilic inflammometer, but also a mediator of bronchomotor tone, but statistically significant relationships have infrequently been obtained with pulmonary function tests (PFT). The aim was to test the hypothesis that the relationships between FENO and PFT could be uncovered by inhaled corticosteroid (ICS) treatment, namely that a link between FENO and bronchodilator response (an index of bronchomotor tone) would appear under ICS.MethodsExhaled NO, forced expiratory flows and lung volumes were measured in atopic asthmatic children without recent (one month) respiratory symptoms.ResultsTwo hundred and thirty children (mean ± SD, age: 11.2 ± 2.5 years, 69 girls) were included (% predicted, FEV1: 100 ± 14; FEF50%: 76 ± 23; RV: 107 ± 29). The relationship between ICS dose (GINA classification) and FENO plateaued in children with an ICS dose higher than 200 μg beclomethasone equipotent daily dose: FENO (median [25th–75th percentiles]), 43 ppb [15–105] (no treatment, n = 65), 33 ppb [15–77] (low dose, n = 70), 23 ppb [12–57] (medium dose, n = 57) and 26 ppb [9–49] (high dose, n = 38). Statistically significant relationships between FENO and PFT were only observed in children receiving more than 200 μg/day ICS: with FEV1 (medium ICS dose: ρ = 0.43, p = 0.001; high dose: ρ = 0.32, p = 0.052) and bronchodilator (400 μg salbutamol) response (medium dose: ρ = 0.54, p = 0.001; high dose: ρ = 0.65, p = 0.002).ConclusionsA positive correlation between FENO and bronchomotor tone appears with increasing ICS doses in atopic children with clinically controlled asthma, which further suggests that children depicting the highest FENO values may have lesser steroid sensitivity.