Pulmonary function testing in COPD typically shows what?

• A. Increased flows
• B. Normal spirometry
• C. Decreased flows (FEV1, FEV1/FVC, FEF25-75)
• D. Decreased DLCO only

Answer: (C)

COPD produces an obstructive pattern on pulmonary function testing, meaning airflow is limited during exhalation due to narrowed airways and loss of elastic recoil. The best-supported finding is a reduced FEV1 along with a decreased FEV1/FVC ratio, reflecting impaired expulsion of air. In addition, flows that reflect small-airways function, such as FEF25-75, are often reduced, indicating involvement of the smaller airways that contribute to the overall obstruction.

Spirometry may show a normal or slightly reduced FVC, and lung volumes can show hyperinflation from air trapping. Diffusion capacity (DLCO) can be reduced in emphysema-dominant COPD, but it is not the sole or defining abnormality and can be normal in other COPD phenotypes. Therefore, the overall pattern centers on decreased expiratory flows rather than increased flows or a normal spirometry, and not “decreased DLCO only.”