High-pitched breath sounds indicate airflow limitation in asymptomatic asthmatic children

Asthmatic children may have airway dysfunction even when asymptomatic, indicating that their long-term treatment is less than optimal. Although airway dysfunction can be identified on lung function testing, performing these tests can be difficult in infants. We studied whether breath sounds reflect subtle airway dysfunction in asthmatic children. The highest frequency of inspiratory breaths sounds (HFI) and the highest frequency of expiratory breath sounds (HFE) were measured in 131 asthmatic children while asymptomatic and with no wheezes for more than 2 weeks. No child was being treated with inhaled corticosteroids (ICS). Breath sounds were recorded and analysed by sound spectrography and compared with spirometric parameters. After initial evaluation, cases with more than step 2 (mild persistent) asthma were treated using inhaled fluticasone (100-200 mu g/day) for 1 month, and then breath sound analysis and pulmonary function testing were repeated. On initial evaluation, HFI correlated with the percentage of predicted FEF50 (%FEF50), (r = -0.45, P < 0.001), the percentage of predicted FEF75 (%FEF75) (r = -0.456, P < 0.001), and FEV1 as a percentage of FVC (FEV1/FVC (%)) (r = -0.32, P < 0.001). HFI did not correlate with the percentage of predicted PEF (%PEF). The 69 children with lower than normal %FEF50 were then treated with ICS. The %FEF50 and %FEF75 improved after ICS treatment, and increases in %FEF50 (P < 0.005) correlated with decreases in HFI (P < 0.001). Higher HFI in asymptomatic asthmatic children may indicate small airway obstruction. Additional ICS treatment may improve the pulmonary function indices representing small airway function with simultaneous HFI decreases in such patients.