The relationship between added lung sounds and airway dimensions

The aim of this study was to explore potential relationships between added lung sound characteristics measured by Computer Aided Lung Sound Analysis (CALSA) and airway dimensions measured by High resolution Computed Tomography (HRCT). CALSA has been proposed as a new objective measurement to record and analyse lung sounds. However, there is still a lack of evidence as to whether and how added lung sounds relate to the geometry of airways. HRCT is considered to have the highest sensitivity of imaging measurements and is capable of generating three dimensional pictures of airways from which the dimensions may be measured. Twenty-six participants (9 healthy non-smokers, 9 healthy smokers and 8 patients with COPD) were recruited. Lung sound data were recorded using a digital stethoscope. HRCT scans were conducted using a Siemens Sensation 64 CT scanner and the resulting data were analysed using the Pulmonary Workstation 2 software to give airway dimensions. Lungs sounds were characterised in terms of Crackle 2-cycle durations (crackle 2CD), the number of crackles per breathing cycle (NCpB) and lung geometry were characterised in terms of airway diameter, length, branching angle, internal perimeter, wall thickness and percentage of wall area. The analysis showed that there was a significant positive correlation between crackle 2CD and airway wall thickness at generations 3 and 5. Crackle 2CD also significantly correlated with the branching angles at the main bronchus and at generation 3. There was also a significant negative correlation between NCpB and percentage of wall area at generation 2 and airway wall thickness at generation 5. Moreover, NCpB recorded at anterior right region of chest wall was found to predict the percentage of wall area at the right upper bronchus. These initial results suggest NCpB might be useful to predict changes in percentage of wall area caused by the chronic inflammation of the main bronchi, though a larger sample size would be needed to confirm it. This suggests that crackles could potentially be used as a biomarker of COPD.