Relationship between concavity of the flow-volume loop and small airway measures in smokers with normal spirometry.

Background: There is increasing evidence of small airway abnormalities in smokers despite normal spirometry. The concavity in the descending limb of the maximum expiratory flow curve (MEFV) is a recognised feature of obstruction and can provide information beyond FEV, and potentially early smoking-related damage. We aimed to evaluate concavity measures compared to known small airway measurements.