Which spirometry pattern defines obstructive lung disease?

• A. FEV1/FVC ratio less than 0.70
• B. FEV1/FVC ratio greater than 0.90
• C. Normal FEV1
• D. Increased FVC

Answer: (A)

Obstructive lung disease shows up as reduced airflow, especially during exhalation, so the amount of air you can blow out in the first second (FEV1) drops more than the total amount you can exhale (FVC). That makes the FEV1/FVC ratio fall. A ratio below 0.70 after bronchodilator is a classic pattern indicating obstruction. The other patterns don’t fit obstructive disease: a very high ratio isn’t typical of obstruction, normal FEV1 doesn’t indicate obstruction, and an increased FVC isn’t a marker of obstructive disease.