## Restrictive Pattern Recognition **Key Point:** The FEV₁/FVC ratio of 1.12 (>0.70) with proportional reduction in both FEV₁ (65%) and FVC (58%) is diagnostic of a **restrictive pattern**. The preserved or elevated FEV₁/FVC ratio distinguishes restriction from obstruction. **High-Yield:** In restrictive disease: - FEV₁/FVC ratio is **preserved or elevated** (typically >0.70, often >0.80) - Both FEV₁ and FVC are reduced **proportionally** - Flow-volume loop maintains normal shape but is reduced in volume - Total lung capacity (TLC) is reduced (would be confirmed by body plethysmography) **Clinical Pearl:** The clinical context (rheumatoid arthritis, bilateral interstitial infiltrates on CXR, insidious dyspnea) points to rheumatoid arthritis-associated interstitial lung disease (RA-ILD). The spirometric pattern confirms parenchymal restriction — the lungs are stiff and cannot expand fully, reducing both FEV₁ and FVC equally. ## Key Distinguishing Features | Feature | Obstructive | Restrictive | |---------|-------------|-------------| | **FEV₁/FVC** | <0.70 ↓ | >0.70 ↑ or normal | | **FEV₁** | ↓ | ↓ | | **FVC** | Normal/↓ | ↓ (proportional to FEV₁) | | **TLC** | Normal/↑ | ↓ | | **Flow-volume loop** | Scooped expiration | Normal shape, reduced volume | | **Cause** | Airway obstruction | Reduced lung/chest wall compliance | **Mnemonic:** **RFR** — Restrictive: Ratio Favors Reduction (FEV₁/FVC preserved); Reduction is Proportional. **Warning:** A preserved FEV₁/FVC ratio is the hallmark of restriction. Do not confuse a ratio of 1.12 (which is >0.70) with obstruction — this is a common exam trap. [cite:Harrison 21e Ch 246]
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