Effects of time, albuterol, and budesonide on the shape of the flow-volume loop in children with asthma

Background: Assessment of asthma through spirometric analysis in children is challenging because of often normal FEV1 values. Objective: We used Mead's slope ratio (SR; (d/dV)/((V)V)) to analyze the shape of the flow-volume loop. Methods: We analyzed the effects of time, albuterol, and budesonide on FEV1, FEV1/forced vital capacity (FVC) ratio, forced expiratory flow from 25% to 75% of expired volume, and Mead's SR both early (between 75% and 50% of FVC, SR61) and late (between 75% and 50% of FVC, SR35) in exhalation in the Childhood Asthma Management Program cohort at baseline, 4 months, and the end of the study in participants who received either inhaled placebo or budesomide twice daily. Results: In the placebo group both SR61 and SR35 improved over time. Bronchodilator consistently improved both SR61 and SR35, without change in degree of improvement over time. Similarly. in the budesonide group time and bronchodilator each independently improved both SR61 and SR35. At 4 months and the end of the study, patients receiving budesonide had significant improvements in SR61 relative to patients receiving placebo, which was independent of bronchodilator effect. Budesonide and placebo were not different with respect to prebronchodilator or postbronchodilator SR35. Conclusion: Budesonide-treated patients have less concave flow-volume loops when compared with placebo-treated patients. Time and bronchodilator also make the flow-volume loop less concave. Furthermore, it appears that there are discrete bronchodilator- and corticosteroid-responsive components of airflow obstruction in pediatric asthma.