reversible airflow obstruction

Imagine pinching a straw to make it harder to sip through, then letting go and finding it flows freely again. Reversible airflow obstruction is the lung equivalent: airways that are narrowed at one moment can open substantially once the constricting muscle relaxes — for instance, after a puff of a bronchodilator.

Technically, it means airway narrowing that improves significantly after bronchodilator treatment, demonstrated on spirometry. A common threshold is a rise in FEV1 of at least 12% and 200 mL after a short-acting bronchodilator, indicating that smooth-muscle constriction (rather than fixed structural damage) is contributing to the obstruction. This responsiveness is a characteristic feature of asthma.

Reversibility supports an asthma diagnosis but is not absolute: people with COPD can show some reversibility, and people with asthma may test non-reversible on a given day if their airways are already open or very narrowed. So a single test is interpreted alongside symptoms, history, and sometimes repeated or challenge testing rather than treated as a yes-or-no verdict.