FEV1/FVC ratio helps differentiate obstructive versus restrictive lung disease. In obstructive diseases, how does the ratio typically present?

• A. Increased
• B. Decreased
• C. Normal
• D. Variable

Answer: (B)

The main concept is that the FEV1/FVC ratio reflects how much of the air in a full breath is expelled in the first second. In obstructive diseases, airway narrowing mainly hampers rapid exhalation, so the FEV1 drops out of proportion to the FVC. That means the ratio falls below normal, often below about 0.7 or the lower limit of normal. This pattern—a reduced FEV1 relative to FVC—is what characterizes obstructive lung disease such as asthma or COPD.

In contrast, restrictive diseases reduce overall lung volumes, so both FEV1 and FVC fall in roughly the same proportion, and the ratio stays normal or can be higher. That difference in how the two values change with obstruction versus restriction is why the ratio is a useful discriminator.

So, in obstructive diseases, the FEV1/FVC ratio is decreased.