## Restrictive Pattern with Emphatic DLCO Reduction **Key Point:** In **restrictive disease**, the FEV₁/FVC ratio is **preserved or elevated** (>0.70) because both flows and volumes are proportionally reduced. ### Spirometric Pattern Analysis | Parameter | Patient Value | Normal | Interpretation | |-----------|---------------|--------|----------------| | FEV₁ | 68% predicted | >80% | Reduced | | FVC | 62% predicted | >80% | **Reduced** | | FEV₁/FVC | 0.82 (82%) | >0.70 | **Preserved/elevated** | | DLCO | 58% predicted | >80% | **Markedly reduced** | **High-Yield:** **Restrictive pattern = Reduced FVC + Preserved FEV₁/FVC ratio.** The key is that the ratio stays normal because airflow obstruction is NOT the problem; the lungs are simply smaller. ### Why DLCO Is Disproportionately Low 1. **Interstitial lung disease (ILD)** thickens the alveolar-capillary membrane 2. **Fibrosis** reduces the surface area available for gas exchange 3. **DLCO reduction (58%) > FVC reduction (62%)** = Parenchymal disease, not just volume loss 4. **Clinical context:** RA + interstitial infiltrates on CXR = RA-associated ILD (rheumatoid lung) **Clinical Pearl:** When DLCO is disproportionately reduced relative to FVC, suspect **parenchymal disease** (fibrosis, emphysema, alveolitis) rather than pure chest wall or neuromuscular restriction. ### Restrictive vs. Obstructive at a Glance | Feature | Restrictive | Obstructive | |---------|-------------|-------------| | FEV₁/FVC | **≥0.70** | **<0.70** | | FVC | Reduced | Normal or mildly reduced | | FEV₁ | Reduced | Reduced | | DLCO | Often reduced (if parenchymal) | Reduced (if emphysema) or normal (if bronchitis) | | Flow-volume loop | Reduced amplitude, normal shape | Scooped expiratory limb | **Mnemonic:** **RESTRICTIVE = Reduced FVC, Ratio Elevated** (RFR) [cite:Harrison 21e Ch 297, Robbins 10e Ch 15]
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