A breath sound analysis in children with cough variant asthma.

Background: Cough variant asthma (CVA) is characterized by a chronic cough and bronchial hyperresponsiveness without confirmation of wheezing. Using a breath sound analyzer, we evaluate the characteristics of breath sound in children with CVA.

Methods: Nine children with CVA (median age, 7.0 years) participated. The existence of breath sounds was confirmed by sound spectrogram. Breath sound parameters, the frequency limiting 50% and 99% of the power spectrum (F and F), the roll-off from 600 to 1200 Hz (Slope) and spectrum curve indices, the ratio of the third and fourth area to the total area of the power spectrum (P/P and P/P) and the ratio of power and frequency at 50% and 75% of the highest frequency of the power spectrum (RPF and RPF) were calculated before and after β agonist inhalation. A spirogram and/or forced oscillation technique were performed in all subjects.

Results: On a sound spectrogram, wheezing was confirmed in seven of nine patients. All wheezing on the image was polyphonic, and they almost disappeared after β agonist inhalation. An analysis of the breath sound spectrum showed that P, P/P, P/P, RPF and RPF were significantly increased after β agonist inhalation.

Conclusions: Children with CVA showed a high rate of inaudible wheezing that disappeared after β agonist inhalation. Changes in the spectrum curve indices also indicated the bronchial reversibility. These results may suggest the characteristics of CVA in children.