A patient with moderate COPD undergoes spirometry. FVC is 3.2 L (predicted 4.0 L), FEV1 is 1.6 L (predicted 3.2 L). What is the FEV1/FVC ratio and what pattern does this represent?

• A FEV1/FVC = 50%; obstructive pattern (normal ratio >70%); both FEV1 and FVC are reduced but FEV1 is disproportionately reduced ✓
• B FEV1/FVC = 50%; restrictive pattern because absolute FVC is below predicted
• C FEV1/FVC = 50%; mixed obstructive and restrictive pattern requiring TLC measurement to confirm
• D FEV1/FVC = 80%; normal pattern because both values are proportionally reduced

Explanation

FEV1/FVC = 1.6/3.2 = 0.50, i.e., 50%. A ratio below 0.70 (70%) defines airflow obstruction (GOLD criterion for COPD). The FEV1 is disproportionately reduced (50% of predicted) compared to FVC (80% of predicted), consistent with obstructive physiology — airflow limitation causes premature small airway closure and air trapping. In a restrictive pattern, both FEV1 and FVC are proportionally reduced, and the FEV1/FVC ratio is normal (>70%) or elevated. While this patient's FVC is below predicted (could reflect gas trapping in COPD, not true restriction), the diagnosis requires TLC measurement to exclude a true restrictive component; however, the primary pattern on spirometry is obstructive. Option D gives an incorrect calculation.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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