Quantitative CT parameters as surrogate markers of small airway dysfunction and discriminators of COPD from asthma

The structural chest computed tomography (CT) correlates of impulse oscillometry (IOS)-defined small airway dysfunction (SAD) and the utility of CT parameters in differentiating COPD from asthma remain incompletely characterized.

This cross-sectional study included patients diagnosed with COPD or asthma at a single center. Quantitative CT parameters included parenchymal indices (LAA%, PRM^fSAD%) and airway wall indices derived by two methods (Pi10-BAND, WA%-BAND, Pi10-FWHM, WA%-FWHM). SAD was defined as R5-R20 >0.07 kPa/L/s. The study outcomes were the associations between CT and IOS parameters, the discriminatory performance of CT parameters for IOS-defined SAD, and their utility in differentiating COPD from asthma.

Among 250 patients (COPD n=166, asthma n=84), SAD was identified in 198 (79.2%). CT airway wall parameters were independently associated with small airway IOS parameters. Pi10-BAND (Odds ratio [OR]=5.85) and WA%-BAND (OR=1.09) were independently associated with SAD and showed the highest discriminatory performance (Area under the curve [AUC]=0.746 and 0.738), outperforming LAA% and PRM^fSAD%. Discriminatory performance was particularly pronounced in asthma (Pi10-BAND AUC=0.850; WA%-BAND AUC=0.844), whereas all CT parameters showed only modest performance in COPD. Only parenchymal CT parameters were independently associated with COPD over asthma (PRM^fSAD%: OR=1.10; LAA%: OR=1.14), despite comparable IOS and spirometric indices between the two conditions.

CT airway wall parameters serve as surrogate markers of airway remodeling associated with IOS-defined SAD, with the greatest utility in asthma, whereas parenchymal CT parameters differentiate COPD from asthma. These findings support the complementary use of quantitative CT and IOS in the evaluation of obstructive lung disease.