Aerodynamic Simulation of Small Airway Resistance: A New Imaging Biomarker for Chronic Obstructive Pulmonary Disease

Purpose: To develop a novel method for calculating small airway resistance using computational fluid dynamics (CFD) based on CT data and evaluate its value to identify COPD.
Patients and Methods: 24 subjects who underwent chest CT scans and pulmonary function tests between August 2020 and December 2020 were enrolled retrospectively. Subjects were divided into three groups: normal (10), high-risk (6), and COPD (8). The airway from the trachea down to the sixth generation of bronchioles was reconstructed by a 3D slicer. The small airway resistance (R_SA) and R_SA as a percentage of total airway resistance (R_SA%) were calculated by CFD combined with airway resistance and FEV₁ measured by pulmonary function test. A correlation analysis was conducted between R_SA and pulmonary function parameters, including FEV₁/FVC, FEV₁% predicted, MEF50% predicted, MEF75% predicted and MMEF75/25% predicted.
Results: The R_SA and R_SA% were significantly different among the three groups (p< 0.05) and related to FEV₁/FVC (r = − 0.70, p < 0.001; r = − 0.67, p < 0.001), FEV₁% predicted (r = − 0.60, p = 0.002; r = − 0.57, p = 0.004), MEF50% predicted (r = − 0.64, p = 0.001; r = − 0.64, p = 0.001), MEF75% predicted (r = − 0.71, p < 0.001; r = − 0.60, p = 0.002) and MMEF 75/25% predicted (r = − 0.64, p = 0.001; r = − 0.64, p = 0.001).
Conclusion: Airway CFD is a valuable method for estimating the small airway resistance, where the derived R_SA will aid in the early diagnosis of COPD.

Keywords: COPD, small airway disease, CT, fluid dynamics