A breath sound analysis in children with cough variant asthma

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.

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 (F₅₀ and F₉₉), 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 (P₃/P_T and P₄/P_T) and the ratio of power and frequency at 50% and 75% of the highest frequency of the power spectrum (RPF₇₅ and RPF₅₀) were calculated before and after β₂ agonist inhalation. A spirogram and/or forced oscillation technique were performed in all subjects.

On a sound spectrogram, wheezing was confirmed in seven of nine patients. All wheezing on the image was polyphonic, and they almost disappeared after β₂ agonist inhalation. An analysis of the breath sound spectrum showed that P_T, P₃/P_T, P₄/P_T, RPF₅₀ and RPF₇₅ were significantly increased after β₂ agonist inhalation.

Children with CVA showed a high rate of inaudible wheezing that disappeared after β₂ agonist inhalation. Changes in the spectrum curve indices also indicated the bronchial reversibility. These results may suggest the characteristics of CVA in children.