Can Quantitative Computed Tomography (qct) Differentiate Between Asthma & Copd in Patients with Similar Degrees of Airflow Limitation?

Background: Airflow limitation is seen in COPD & asthma. Aim: Using QCT we sought to determine differences between asthma and COPD subjects grouped by airflow limitation. Material & Methods: COPD (n=81), asthma (n=171) & healthy (n=49) subjects had clinical & physiological characterization. COPD & Asthma subjects were split based on FEV1% predicted; Group 0>80%, Group 1 50-80% and Group 2<50%. QCT included average lumen area of segmental bronchi corrected for body surface area (LA/BSA), mean lung density expiratory/inspiratory ratio (MLDE/I), 15th percentile point (Perc15) & fractal dimension of low attenuation clusters in inspiration (LAC-D-950). Results: Asthmatics with moderate airflow limitation have smaller median (IQR) LA/BSA (mm2/m2) when compared to asthmatics with no airflow limitation & COPD with moderate airflow limitation; 9.28[8.28-10.83] v11.15[9.56-13.04]; 11.32[9.63-13.33],p<0.05 respectively. Perc15 is not significantly different between asthmatics with severe airflow limitation & COPD with moderate airflow limitation;-955[-966 to -949] v-958[-971 to -947]HU respectively, but is significantly different (p<0.05) between asthmatics with no airflow limitation & healthy controls. However LAC-D-950 is significantly different between asthmatics with severe airflow limitation & COPD groups 1 & 2; 1.91[1.87-1.96] v1.85[1.78-1.92]; 1.81[1.72-1.89],p<0.05 respectively. Conclusion: Asthmatics with moderate airflow limitation show LA/BSA narrowing compared to spirometrically similar COPD. QCT measured Emphysema may be overestimated in asthmatics with severe airflow limitation as LAC-D-950 remains different between them and COPD. Funded by AirPROM.