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Regional airflow obstruction after bronchoconstriction and subsequent bronchodilation in subjects without pulmonary disease.

Some asthmatic subjects have ventilation defects that are resistant to bronchodilator therapy, and it is thought that these resistant defects may be due to ongoing inflammation or chronic airway remodeling. However, it is unclear whether regional obstruction due to bronchospasm alone persists after bronchodilator therapy. To investigate this, six young, healthy subjects - in whom inflammation and remodeling were assumed to be absent - were bronchoconstricted with a PC20 dose of methacholine and subsequently bronchodilated with a standard dose of albuterol on three separate occasions. Specific ventilation imaging - a proton MRI technique - was used to spatially map specific ventilation across 80% of each subject's right lung in each condition. The ratio between regional specific ventilation at baseline and after intervention was used to classify areas that had constricted. After albuterol rescue from methacholine bronchoconstriction, 12% (9%) [mean (SD)] of the lung was classified as constricted. Of the 12% of lung units that were classified as constricted after albuterol, approximately half [7% (7%)] had constricted after methacholine and failed to recover, while half [6% (4%)] had remained open after methacholine but became constricted after albuterol. The incomplete regional recovery was not reflected in the subjects' FEV1 measurements - which did not decrease from baseline (P=0.97) - nor was it detectable as an increase in specific ventilation heterogeneity (P=0.78).