The Relationship Between Crackle Characteristics and Airway Morphology in COPD

Crackles in COPD are believed to be generated by the re-opening of collapsed airways, which result from chronic inflammation, secretions, and loss of cartilaginous support through inflammation. However, it is unclear whether crackle characteristics can be used to identify COPD. This is the first study to examine the relationship between specific added lung sounds (crackles) and measurements of conductive airways and emphysema score obtained from high-resolution computed tomography (HRCT) in vivo in humans. A predictive relationship might permit the use of lung sounds as a biomarker for COPD.

A convenience sample of 26 subjects was recruited into the study and consisted of 9 healthy non-smokers, 9 healthy smokers, and 8 subjects with mild or moderate COPD. Lung sound data were recorded using a digital stethoscope connected to a laptop computer. Airway diameter, emphysema score, and percentage of wall area were measured from HRCT scans.

The analysis showed that there were no statistically significant differences in crackle characteristics (the number of crackles per breathing cycle and crackle 2-cycle duration) between the 3 subject groups. Both crackle 2-cycle duration and crackle number showed some significant correlation with airway parameters at some branch generations, but due to the large number of correlations performed, these were consistent with chance findings.

Although there were some significant correlations between crackle characteristics and measurements of the conductive airways and emphysema score, the possibility that these correlations have occurred by chance cannot be ruled out. Therefore, this study provides no conclusive evidence that crackle characteristics are related to HRCT variables in COPD.