## Restrictive Pattern in Pulmonary Fibrosis This patient demonstrates a **restrictive spirometric pattern** characteristic of interstitial lung disease (ILD) from systemic sclerosis–associated pulmonary fibrosis. ### Spirometric Pattern Analysis | Parameter | Patient Value | Interpretation | |-----------|---------------|----------------| | FEV₁/FVC ratio | 0.82 (82%) | **Normal or elevated** (>0.70) | | FEV₁ | 68% predicted | Mildly reduced | | FVC | 55% predicted | **Significantly reduced** | | TLC | 58% predicted | **Reduced** (restrictive pattern) | | RV | 40% predicted | Reduced | **Key Point:** The **hallmark of restrictive disease is reduced TLC**. The FEV₁/FVC ratio is normal or elevated because both FEV₁ and FVC are reduced proportionally, but the airways remain patent and non-obstructed. ### Pathophysiology of Fibrosis-Induced Restriction 1. **Collagen deposition** — fibroblasts proliferate and deposit excessive collagen in the interstitium 2. **Alveolar loss** — fibrosis obliterates alveolar spaces, reducing total surface area available for ventilation 3. **Decreased compliance** — fibrotic tissue is stiff and non-compliant; the lungs require greater pressure to inflate 4. **Reduced TLC** — the stiff lungs cannot expand fully, limiting maximum inspiratory volume 5. **Proportional reduction of FEV₁ and FVC** — both are reduced, preserving the ratio **Clinical Pearl:** The **FEV₁/FVC ratio ≥0.80** in a patient with reduced TLC is the diagnostic hallmark of restriction and helps distinguish it from obstruction (where FEV₁/FVC <0.70). ### Restrictive vs. Obstructive Comparison ```mermaid flowchart TD A[Spirometry]:::decision --> B{FEV₁/FVC ratio}:::decision B -->|< 0.70| C[Obstructive Pattern]:::outcome B -->|≥ 0.70| D{TLC status}:::decision D -->|Reduced| E[Restrictive Pattern]:::outcome D -->|Normal| F[Normal Spirometry]:::outcome C --> G[↑ RV, ↑ TLC<br/>Air trapping]:::action E --> H[↓ RV, ↓ TLC<br/>Reduced lung volume]:::action ``` **High-Yield:** In **restrictive disease**: - FEV₁/FVC is **normal or elevated** (≥0.70) - **TLC is reduced** (<80% predicted) - Both FEV₁ and FVC are reduced proportionally - RV is reduced (not elevated) - Causes: fibrosis, sarcoidosis, pneumoconiosis, ILD, chest wall disease, neuromuscular disease **Mnemonic:** **RESTRICT = Reduced Everything** - **R**educed TLC (cardinal finding) - **E**levated FEV₁/FVC ratio - **S**tiff lungs (↓ compliance) - **T**ight interstitium (fibrosis) - **R**educed RV - **I**nterstitial disease (common cause) - **C**ollapsed alveoli - **T**otal volume ↓ ### Why Fibrosis Causes Restriction Fibrotic tissue replaces normal elastic lung parenchyma. The lungs become **stiff and non-compliant**, requiring greater inspiratory pressure to inflate. The maximum volume the lungs can achieve (TLC) is therefore limited. Airway patency is preserved, so FEV₁/FVC remains normal. [cite:West Respiratory Physiology 10e Ch 3; Harrison 21e Ch 299]
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