Changes in the breath sound spectrum during methacholine inhalation in children with asthma

Background and objective An effort-independent breath sound analysis is expected to be a safe and simple method for clinical assessment of changes in airway function. The effects of bronchoconstriction and bronchodilation on novel breath sound parameters in asthmatic children were investigated. Methods The study population included 49 children with atopic asthma (male = 33; mean age: 10.2 years). We evaluated breath sound parameters of the highest frequency of the power spectrum (HFp), frequency limiting 50% and 99% of the power spectrum (F50 and F99) and roll-off from 600 Hz to the HFp (Slope). We also assessed new parameters obtained using the ratios of sound spectrum parameters (spectrum curve indices), such as the ratio of the third and fourth power area to the total power area (P3/PT and P4/PT), the ratio of the third and fourth areas to the total area under the curve (A3/AT and B4/AT) and the ratio of power and frequency at 75% of HFp and 50% of HFp (RPF75 and RPF50). This was measured before and after methacholine inhalation challenge and after β2 agonist inhalation. Results The parameters, F50 and F99, showed no changes after methacholine inhalation. Conversely, the A3/AT (12.5–10.0%, P < 0.001), B4/AT (7.6–5.5%, P < 0.001), RPF75 (6.7–4.0 dBm/Hz, P < 0.001) and RPF50 (5.8–4.3 dBm/Hz, P < 0.001) were significantly decreased. These values returned to the original level after β2 agonist inhalation. Conclusion Spectrum curve indices indicate bronchoconstriction and bronchodilation. These parameters may play a role in the assessment of airway narrowing in asthmatic children.