Changes in the breath sound spectrum with bronchodilation in children with asthma

Abstract Background Breath sound parameters have been suggested to be new biomarkers of airway function in patients with asthma. Methods We investigated the effect of bronchodilation on breath sound parameters in sixty-four children (mean age, 8.9 years; range, 6–16 years) using a breath sound analyzer. The breath sound parameters included frequency limiting 50% and 99% of the power spectrum (F 50 and F 99 ), roll-off from 600–1200 Hz (slope), and spectrum curve indices such as the ratios of the third and fourth power area to the total area of the power spectrum (P 3 /P T and P 4 /P T ), total area under the curve (A 3 /A T and B 4 /A T ), and the ratio of power and frequency at 50% and 75% of the highest frequency of the power spectrum (RPF 75 and RPF 50 ). Lung function was assessed using spirometry and the forced oscillation technique (FOT). All variables were assessed before and after inhalation of a β 2 -agonist. Results The spectrum curve indices, A 3 /A T , B 4 /A T , RPF 75 , and RPF 50 , showed statistically significant increase following β 2 -agonist inhalation. The increase in RPF 50 was correlated with the decrease in the difference between resistance at 5 Hz and 20 Hz, R5-R20, measured by FOT. In the multiple regression analysis adjusted for the effect of ΔRPF 75 , the changes in A 3 /A T and B 4 /A T were positively correlated with that in the forced expiratory volume in one second. Conclusions The spectrum curve indices indicated bronchodilation, and may be useful for the assessment of bronchial reversibility in children with asthma.