Spirometric parameters in pulmonary function test (PFT) can provide information on fixed airflow obstruction (FAO) usually associated with difficulty in treatment, an accelerated decline in lung function, and excess morbidity in asthmatic patients. Recently, quantitative computed tomography (QCT) and its post-processing become a useful tools to derive more detailed airway structure, parenchymal function, as well as computational flow features.

 In this study, we aimed to demonstrate structural and functional differences between asthma with FAO and asthma without FAO. Two sets of the QCT images of asthmatic patients without FAO (group A, N=40) and with FAO (group B, N=12) were employed. Structural and functional QCT-derived variables of airways were extracted to assess lung function. A one-dimensional (1D) computational fluid dynamics (CFD) model considering airway deformation was applied to compare the pressure distribution and hysteresis curve between the two groups.

 For QCT-derived structures, the airway wall in small regions was thicker in group B during inspiration. The 1D CFD-derived pressures showed strong correlations with the PFT-based metrics, while QCT-derived structural variables were not correlated. The computational pressure indicated that the narrowed airways of Group B caused a greater pressure drop and workload during breathing.

In conclusion, asthmatics with and without FAO showed different lung functions, airway structures, and pressure distribution in small airways which may improve our understanding of the irreversible airway obstructive mechanism and aid in the development of future therapies for this type of disease.