Fig. 2

A The imaging measurement parameters for MLD, PRM^fSAD and lumen area of sixth bronchus in three patients with normal lung function, PRISm and moderate COPD. The blue color in the first column represents the area with a CT value less than − 950 HU on inspiratory CT. In the PRM obtained from inspiration and expiration CT, red represents the emphysema area, yellow represents the functional small airway disease area, and green represents the normal lung tissue area. The last column is the 3D bronchial tree, and the four small images on the right represent sections of the sixth bronchus. The normal patient was a 56-year-old man (FEV1%pred = 121.0%, FEV1/FVC% = 94.27%). The MLD was − 851.7 HU; the emphysema, fSAD and normal percent of PRM was 1.5%, 11% and 87.5%; the lumen area of the sixth bronchus was 10.4 mm². The patient with PRISm was a 52-year-old man (FEV1%pred = 76.4%, FEV1/FVC% = 70.63%). The MLD was − 798.0 HU; The emphysema、fSAD and normal percent of PRM was 12%, 24% and 64%; The lumen area of was the sixth bronchus 5.4 mm². The patient with GOLD 2 was a 68-year-old man (FEV1% pred = 58%, FEV1/FVC% = 69.11%). The MLD was − 863.6 HU; The emphysema, fSAD and normal percent of PRM was 29%, 36% and 35%; the lumen area of the sixth bronchus was 5.8 mm². B The bar chart shows that there were significant differences in the parameters of MLD, PI-1 and PI-15 among the three groups of normal, PRISm and mild to moderate COPD, especially in MLD. C The bar chart shows that there were significant differences in PRM^Emph between PRISm and mild to moderate COPD, as well as PRM^fSAD between the normal and PRISm patients