Study objectives: To determine respective contributions of alveolar and proximal airway compartments in exhaled nitric oxide (NO) output (Q̇no) in pediatric patients with asthma and to correlate their variations with mild symptoms or bronchial obstruction.
Patients and design: In 15 asthmatic children with recent mild symptoms, 30 asymptomatic asthmatic children, and 15 healthy children, exhaled NO concentration was measured at multiple expiratory flow (V̇) rates allowing the calculation of alveolar and proximal airway contributions in Q̇no, using two approaches, ie, linear and nonlinear models.
Measurements and results: Asymptomatic and recently symptomatic patients were not significantly different regarding FEV1 and maximum V̇ between 25% and 75% of FVC (MEF25–75): FEV1, 93.3 ± 13.4% vs 90 ± 7.5%; MEF25–75, 70 ± 22% vs 68 ± 28% of predicted values, respectively (mean ± SD). Maximal airway Q̇no output was significantly higher in recently symptomatic vs asymptomatic patients (p < 0.0001), and in asymptomatic patients vs healthy children (p < 0.02): 134 ± 7 nl/min, 55 ± 43 nl/min, and 19 ± 8 nl/min, respectively. In a multiple regression analysis, variables that influenced airway Q̇no output were symptoms (p < 0.0001) and distal airway obstruction as assessed by MEF25–75 (p < 0.05). Alveolar NO concentration (FAno) was significantly (p < 0.03) higher in recently symptomatic than in patients without symptoms, whereas it was not significantly different between asymptomatic patients and healthy children: 7.2 ± 2.4 parts per billion (ppb), 5.5 ± 2.7 ppb, and 4.2 ± 2.0 ppb, respectively.
Conclusions: An increase in FAno was observed in the presence of symptoms, and proximal airway NO output was correlated with distal obstruction during asthma.