Respiratory Sound Intensity as a Noninvasive Acoustic Biomarker in COPD

Chronic obstructive pulmonary disease (COPD) is a common respiratory disease and a leading cause of death worldwide. Due to the clinical heterogeneity of COPD and the low specificity of the spirometric tests currently used for diagnosing COPD, it is often under-diagnosed. The aim of this work is to explore the potential use of respiratory sound (RS) intensity as a noninvasive acoustic biomarker for the diagnosis and monitoring of COPD. Flow and RS signals were recorded in 15 healthy controls, 7 mild COPD patients, and 5 severe COPD patients, during the performance of a variable inspiratory flow protocol. RS intensity was estimated using fixed sample entropy. RS intensity showed a very strong correlation with respiratory flow in all participants. RS intensity and flow increased similarly during the variable inspiratory flow protocol. However, the increasing pattern of the two measures was different between healthy controls and COPD patients, with lower increases in COPD patients. RS intensity is therefore sensitive to altered respiratory mechanics in COPD and could therefore be used as a noninvasive acoustic biomarker for monitoring COPD patients.