What finding during pulmonary function testing is indicative of asthma?

Reversible obstruction with a decrease in FEV1 (forced expiratory volume in 1 second) is a hallmark finding indicative of asthma. In asthma, the airways are hyperreactive, leading to bronchoconstriction and inflammation. During pulmonary function testing, patients with asthma often show a significant decrease in FEV1, especially after exposure to a bronchodilator, which reverses this obstruction.

The key feature of asthma is its reversible nature; after the administration of a bronchodilator, an increase in FEV1 indicates that the obstruction was not fixed and is responsive to treatment. This characteristic helps differentiate asthma from other lung diseases, such as chronic obstructive pulmonary disease (COPD), where airway obstruction is typically less reversible.

While an increased FEV1/FVC ratio suggests restrictive lung disease, flat tidal volume is not typically associated with asthma. Normal lung volumes may be seen in some individuals, but they do not specifically indicate asthma as they can occur in a variety of other conditions. Thus, the finding of reversible obstruction with decreased FEV1 serves as a strong indication of asthma during pulmonary function testing.