Which spirometry result best identifies obstructive lung disease?

Which spirometry result best identifies obstructive lung disease?

• A. FVC
• B. FEV1
• C. FEV1/FVC
• D. Peak expiratory flow

Answer: (B)

Obstruction is best identified by a disproportionate drop in expiratory flow relative to lung volume. The ratio of FEV1 to FVC captures this: FEV1 is how much air you can force out in the first second, and FVC is the total air exhaled. In obstructive disease, airway narrowing slows the initial, rapid portion of exhalation, so FEV1 declines more than FVC, lowering the FEV1/FVC ratio. FEV1 alone can be reduced in both obstructive and restrictive conditions, so it doesn’t distinguish the pattern by itself. FVC reflects overall lung volume and can be reduced for reasons other than obstruction, while peak expiratory flow is highly effort-dependent and less reliable for diagnosing obstruction. Thus, the FEV1/FVC ratio is the best single indicator of obstructive physiology, with a reduced value suggesting obstruction.

Obstruction is best identified by a disproportionate drop in expiratory flow relative to lung volume. The ratio of FEV1 to FVC captures this: FEV1 is how much air you can force out in the first second, and FVC is the total air exhaled. In obstructive disease, airway narrowing slows the initial, rapid portion of exhalation, so FEV1 declines more than FVC, lowering the FEV1/FVC ratio. FEV1 alone can be reduced in both obstructive and restrictive conditions, so it doesn’t distinguish the pattern by itself. FVC reflects overall lung volume and can be reduced for reasons other than obstruction, while peak expiratory flow is highly effort-dependent and less reliable for diagnosing obstruction. Thus, the FEV1/FVC ratio is the best single indicator of obstructive physiology, with a reduced value suggesting obstruction.