Objective evaluation of wheezing in normal infants

Background: To evaluate the frequency of wheezing in infants, the presence of wheezing was examined in normal infants using a breath sound analyzer, METHODS: A total of 443 infants (age range, 3-24 months) were included in the present study. The existence of audible wheezing and faint wheezing/inaudible wheezing-like noises (FW) was confirmed on chest auscultation and a sound spectrogram. The breath sound parameters of the sound spectrum, frequency limiting 99% of power spectrum (F₉₉ ), roll-off from 600 to 1,200 Hz (slope) and spectrum curve indices, total area under the curve of dB data (A₃ /A_T and B₄ /A_T ), and ratio of power and frequency at 50% and 75% of the highest frequency of the power spectrum (RPF₅₀ and RPF₇₅ ) were calculated. Using an original Japanese questionnaire, we examined the characteristics of the airway condition of all infants.

Results: Finally, a total of 398 infants were analyzed in the present study, and 283 were in good health while 115 had acute respiratory infection (ARI) in the last 7 days. No infants had audible wheezing on auscultation. Three infants without ARI (1.1%) and 10 infants with ARI (8.7%) had FW. In the evaluation of breath sound parameters, there were no marked differences between the infants with and without FW.

Conclusions: Using a breath sound analyzer, wheezing and FW were recognized in only a few infants in good health. Infants recognized to have audible wheezing in daily practice may be at risk of developing recurrent wheezing/asthma.