Which statement about the FEV1/FVC ratio is true?

Which statement about the FEV1/FVC ratio is true?

• A. It is the absolute volume exhaled in the first second.
• B. It is the total volume exhaled during a full breath.
• C. It is the ratio of FEV1 to FVC; a value below 0.9 indicates obstruction.
• D. It is the ratio of FEV1 to FVC, and a value below 0.7 indicates obstruction.

Answer: (D)

The key idea is understanding what the FEV1/FVC ratio means and how it signals obstruction. FEV1 is the amount of air you can forcefully blow out in the first second of a forced exhale, while FVC is the total amount you can exhale forcefully after a full inhale. The ratio compares these two quantities to gauge how quickly air can be expelled relative to the total exhaled volume. In obstructive airway diseases like asthma or COPD, narrowing of the airways reduces the speed of exhalation more than the total volume, so FEV1 drops more than FVC. This lowers the FEV1/FVC ratio. A commonly used threshold is 0.7; when the ratio falls below 0.7, obstruction is suggested. So the statement is true because it correctly defines the ratio as FEV1 divided by FVC and correctly notes that a value below 0.7 indicates obstruction. The other options describe FEV1 or FVC incorrectly: FEV1 alone is the first-second volume, not the ratio; FVC is the total exhaled volume, not the ratio.

The key idea is understanding what the FEV1/FVC ratio means and how it signals obstruction. FEV1 is the amount of air you can forcefully blow out in the first second of a forced exhale, while FVC is the total amount you can exhale forcefully after a full inhale. The ratio compares these two quantities to gauge how quickly air can be expelled relative to the total exhaled volume.

In obstructive airway diseases like asthma or COPD, narrowing of the airways reduces the speed of exhalation more than the total volume, so FEV1 drops more than FVC. This lowers the FEV1/FVC ratio. A commonly used threshold is 0.7; when the ratio falls below 0.7, obstruction is suggested.

So the statement is true because it correctly defines the ratio as FEV1 divided by FVC and correctly notes that a value below 0.7 indicates obstruction. The other options describe FEV1 or FVC incorrectly: FEV1 alone is the first-second volume, not the ratio; FVC is the total exhaled volume, not the ratio.