A patient has FVC 3.0 L, FEV1 2.5 L, FEV1/FVC 83%, TLC 5.5 L, RV 2.5 L, DLCO 45% predicted. Which pattern does this represent?
- A Obstructive pattern with air trapping
- B Restrictive pattern with proportional reduction of lung volumes; high RV/TLC suggests air trapping however
- C Restrictive pattern: FVC reduced, FEV1/FVC preserved or elevated, TLC reduced, low DLCO suggesting interstitial lung disease ✓
- D Mixed obstructive-restrictive pattern with emphysema (low DLCO indicates alveolar destruction)
Explanation
FEV1/FVC of 83% (>70%) with reduced FVC (absolute value 3.0 L is below predicted for most adults) indicates a restrictive pattern. The TLC of 5.5 L may be mildly reduced (normal ~6–7 L in adult males), consistent with restriction. Critically, DLCO at 45% predicted is markedly reduced, indicating impaired gas exchange consistent with interstitial lung disease (ILD) — thickened alveolar-capillary membrane reduces diffusion. In pure ILD, RV may be normal or slightly reduced. Low DLCO with restrictive spirometry and reduced TLC strongly points to ILD (e.g., IPF, hypersensitivity pneumonitis). Obstructive pattern requires FEV1/FVC <70%.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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