Small airway dysfunction and its role in pediatric asthma control assessment

Background: Previous reports suggest that small airway dysfunction (SAD) is associated with poor asthma control. Objective: To determine the usefulness of the study of the SAD in assessing asthma control. Methods: A cross-sectional study was performed in children aged between 6-15 years old diagnosed with moderate asthma and FEV 1 >80% at the time of inclusion.A forced spirometry,a determination of R5-R20 by impulse oscillometry , a plethysmography and a bronchodilator test were performed.Exhaled nitric oxide (NO) at multiple flow rates was measured and alveolar NO concentration (CA NO ) was calculated.Asthma Control Questionnaire Test (ACT) and Asthma Quality of Life Questionnaire were completed by patients (PAQLQS) and caregivers (PACQLQ).The prevalence of the SAD was defined by the presence of one or more of the following criteria:CA NO ≥4.5ppb,RV/TLC≥33%,R5-R20 ≥0.147kPa/L/s and FEF 25-75 NO ,R5-R20, RV/TLC, FEF 25-75, PAQLQS/PACQLQ and ACT was studied using Spearman9s rho and Pearson9s chi-squared test ( χ 2 ). Results: 100 subjects were studied distributed into group 1 (poor control, n=29) and 2 (good control, n=71). At least 1 criteria of SAD was found in 59% and 2 criteria in 27%.R5-R20 was increased in 49%, RV/TLC in 20%, CA NO in 7% and FEF 25-75 was decreased in19%.FEF 25-75 and PAQLQS/PACQLQ scores were significantly lower in group 1.Moderate correlation was found between FEF 25-75 and R5-R20. No association was found to establish the degree of asthma control among the rest of the variables studied. Conclusion: In our sample, SAD was found in more than half of asthmatic children, but only FEF 25-75 provides additional information to assess asthma control.