Fig 1 -

(A) Algorithm used to interpret PFTs. (B) Small airway disease index (SADI), which is the angle formed by two linear regression lines on the flow-volume loop (FVL). The first line is the fitting to the segment between the point at the peak expiratory flow (point A) and the point at 75% of the expiratory vital capacity (Point B). The second line is the fitting to the segment between point B and the point where the expiratory portion of the FVL intersects with the x-axis (point C)(Front Physiol 13:914972, 2022). LLN: Low limit of normal.