Forced midexpiratory flow between 25% and 75% of forced vital capacity is associated with long-term persistence of asthma and poor asthma outcomes

Background Whether small-airway obstruction contributes to the long-term evolution of asthma remains unknown. Objectives Our aim was to assess whether the level of forced midexpiratory flow between 25% and 75% of forced vital capacity (FEF25-75 ) was associated with the persistence of current asthma over 20 years and the subsequent risk for uncontrolled asthma independently of FEV1. Methods We studied 337 participants (142 children and 225 adults) with current asthma (asthma attacks or treatment in the past 12 months) recruited to the Epidemiological Study on the Genetics and Environment of Asthma (EGEA1) and followed up at the 12- and 20-year surveys. Persistent current asthma was defined by current asthma reported at each survey. A lung function test and a methacholine challenge test were performed at EGEA1 and EGEA2. Adjusted odds ratios (ORs) were estimated for FEF25-75 decreased by 10% of predicted value. Results A reduced level of FEF25-75 at EGEA1 increased the risk of long-term asthma persistence (adjusted OR, 1.14; 95% CI, 1.00-1.29). In children the association remained significant after further adjustment for FEV1 and in participants with FEV1 of greater than 80% of predicted value. A reduced FEF25-75 level at EGEA1 was significantly associated with more severe bronchial hyperresponsiveness ( P