## Restrictive Lung Disease Pattern on Spirometry **Key Point:** A restrictive pattern is defined by reduced TLC (<80% predicted) with a normal or elevated FEV₁/FVC ratio (≥0.70), reflecting proportional reduction in both FEV₁ and FVC. ### Spirometric Findings in Restriction | Parameter | This Patient | Interpretation | |-----------|--------------|----------------| | FEV₁/FVC | 1.10 (>0.70) | **Normal ratio** — hallmark of restriction | | TLC | 72% predicted | **Reduced** — defines restrictive disease | | RV | 40% predicted | **Reduced** — lungs cannot expand | | FVC | 58% predicted | Reduced due to stiff lungs | | FEV₁ | 65% predicted | Reduced proportionally with FVC | **High-Yield:** The **FEV₁/FVC ratio ≥0.70 with reduced TLC** is the gold standard for identifying restriction. This distinguishes it from obstruction (FEV₁/FVC <0.70) and from normal lungs. ### Pathophysiology of Asbestos-Induced Fibrosis 1. Asbestos fibers → chronic inflammation and fibroblast activation 2. Progressive collagen deposition → lung stiffness (reduced compliance) 3. Stiff lungs cannot expand → TLC and RV both decrease 4. Expiratory flow is preserved because airways remain patent 5. Result: proportional reduction in FEV₁ and FVC → normal ratio **Clinical Pearl:** Bilateral lower-lobe fibrosis on imaging is classic for asbestos-related pulmonary fibrosis. The 40-year latency period and occupational exposure history are typical. ### Why FEV₁/FVC Stays Normal in Restriction - In restriction, both FEV₁ and FVC are reduced by the same mechanism (stiff lungs) - The ratio remains ≥0.70 because neither is disproportionately affected - In obstruction, FEV₁ falls more than FVC → ratio <0.70 **Mnemonic:** **REST** = **R**educed TLC, **E**levated FEV₁/FVC ratio, **S**tiff lungs, **T**ypical of fibrosis.
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