Which spirometry pattern represents obstructive disease?

Which spirometry pattern represents obstructive disease?

• A. FEV1 decreased more than FVC
• B. FVC decreased more than FEV1
• C. FEV1/FVC increased
• D. Both FEV1 and FVC decrease equally

Answer: (A)

In obstructive disease, the airflow limitation during expiration causes a greater drop in how much air you can blow out in the first second (FEV1) than in the total exhaled volume (FVC). This makes the FEV1/FVC ratio fall below normal. FVC may be normal or only mildly reduced, so the bigger relative drop in FEV1 is the telltale sign. If FVC dropped more than FEV1, or if the ratio stayed normal or increased, that wouldn’t fit obstruction. If both values fell by about the same amount, the ratio would stay roughly normal as well. So, FEV1 decreased more than FVC best represents obstructive disease.

In obstructive disease, the airflow limitation during expiration causes a greater drop in how much air you can blow out in the first second (FEV1) than in the total exhaled volume (FVC). This makes the FEV1/FVC ratio fall below normal. FVC may be normal or only mildly reduced, so the bigger relative drop in FEV1 is the telltale sign. If FVC dropped more than FEV1, or if the ratio stayed normal or increased, that wouldn’t fit obstruction. If both values fell by about the same amount, the ratio would stay roughly normal as well. So, FEV1 decreased more than FVC best represents obstructive disease.