Bronchodilators increase airway instability in XXXX .

@entity1 @entity1577
Supramaximal flow transients of partial expiratory flow-volume curves are caused by a rapidly emptying compartment. By superimposing a maximal and a series of partial expiratory flow-volume curves, the volume of the flow transient equivalent for the maximal curve was estimated (volume of airway contribution = VACMEFV). This flow transient equivalent is caused by an extra dead space, created in the large airways by a full inspiration. In 18 @entity1 with @entity1577 ( @entity1577 ), routine pulmonary functions and VACMEFV were measured before and after bronchodilator medication. Baseline VACMEFV correlated directly with the curvilinearity of the flow-volume curve and inversely with the clinical and radiologic score. Significantly, bronchodilator medication improved FVC, FEV1, FEF25-75, VC, PEF, Raw, and also VACMEFV. In 6 @entity1 , VEmax25 increased as a result of apparent peripheral bronchodilation. In 3 others, end-expiratory flow increased slightly but the expanded VACMEFV included the measuring point invalidating the measurement. In the remaining 9 @entity1 , VEmax25 decreased after bronchodilator. As an apparent discrepancy, FEV1, FVC, PEF, VC, FEF25-75 increased, and Raw decreased in 4 to 9 @entity1 . The volumes and flow rates measured early in forced expiration and the end-expiratory flow behaved differently because VACMEFV expanded beyond the measuring points of early expiratory and mid-expiratory flow rates. As the bronchodilator rendered the compliant large airways still more distensible, the amount of air emptied from the dead space in early forced expiration increased. Simultaneously, end-expiratory flow decreased because of enhanced airway compression.(ABSTRACT TRUNCATED AT 250 WORDS)
