When a "wheeze" is not a wheeze: acoustic analysis of breath sounds in infants

Epidemiological studies indicate that the prevalence of "wheeze" is very hi gh in early childhood. However, it is clear that parents and clinicians fre quently use the term "wheeze" for a range of audible respiratory noises. Th e commonest audible sounds originating from the lower airways in infancy ar e ruttles, which differ from classical wheeze in that the sound is much low er in pitch,,vith a continuous rattling quality and lacking any musical fea tures. The aim of this study was to clearly differentiate wheeze and ruttle s objectively using acoustic analysis. Lung sounds were recorded in 15 infants, seven with wheeze and eight with r uttles, using a small sensitive piezoelectric accelerometer, and informatio n relating to the respiratory cycle was obtained using inductive plethysmog raphy. The acoustic signals were analysed using a fast fourier transformati on technique (Respiratory Acoustics Laboratory Environment programme). The acoustic properties of the two noises were shown to be quite distinct, the classical wheeze being characterized by a sinusoidal waveform with one or more distinct peaks in the power spectrum display; the ruttle is represe nted by an irregular nonsinusoidal waveform,vith diffuse peaks in the power spectrum and with increased sound intensity at a frequency of <600 Hz. It is important for clinicians and epidemiologists to recognize that there are distinct types of audible respiratory noise in early life with characte ristic acoustic properties.