## Restrictive Lung Disease Pattern **Key Point:** The FEV₁/FVC ratio of 0.88 (> 0.70) is the defining feature of restrictive lung disease. Combined with reduced FVC, FEV₁, TLC, and DLCO, this confirms pulmonary fibrosis. ### Spirometric Interpretation | Parameter | Value | Interpretation | |-----------|-------|----------------| | FEV₁ | 68% predicted | Mildly reduced | | FVC | 62% predicted | Reduced | | FEV₁/FVC | 0.88 | **Restrictive pattern (> 0.70)** | | TLC | 72% predicted | Reduced (confirms restriction) | | DLCO | 58% predicted | Significantly reduced | **High-Yield:** In restrictive disease, both FEV₁ and FVC are reduced proportionally, so the ratio stays normal or elevated (> 0.70). The reduced TLC confirms true restriction. Reduced DLCO in the context of interstitial fibrosis indicates alveolar-capillary inflammation and thickening. ### Why This Pattern Indicates Pulmonary Fibrosis 1. **Preserved FEV₁/FVC ratio** (0.88): Airways are not obstructed; the lungs simply have reduced volume 2. **Reduced TLC** (72%): Confirms true restriction, not just low FVC from poor effort 3. **Reduced DLCO** (58%): Indicates thickened alveolar-capillary membrane (hallmark of fibrosis) 4. **Clinical context**: RA-associated interstitial lung disease (RA-ILD) is a common extra-articular manifestation **Clinical Pearl:** The combination of reduced FVC, normal/elevated FEV₁/FVC, reduced TLC, and disproportionately reduced DLCO is pathognomonic for pulmonary fibrosis. DLCO is often the most sensitive early marker of ILD. **Mnemonic: RESTRICTIVE = FEV₁/FVC > 0.70 + Low TLC + Low FVC** — the ratio stays "normal" because both numerator and denominator shrink together.
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