## FEV₁/FVC Ratio and Spirometric Patterns ### Interpretation of FEV₁/FVC Ratio **Key Point:** The FEV₁/FVC ratio is the gold standard for distinguishing obstructive from restrictive patterns in spirometry. | Pattern | FEV₁/FVC Ratio | FEV₁ | FVC | TLC | RV | |---------|----------------|------|-----|-----|----| | **Normal** | ≥ 0.70 (≥ 70%) | Normal | Normal | Normal | Normal | | **Obstructive** | < 0.70 (< 70%) | ↓ Reduced | Normal or ↓ | ↑ Increased | ↑ Increased | | **Restrictive** | ≥ 0.70 (≥ 70%) | ↓ Reduced | ↓ Reduced | ↓ Reduced | Normal or ↓ | | **Mixed** | < 0.70 (< 70%) | ↓ Reduced | ↓ Reduced | Variable | Variable | ### Analysis of FEV₁/FVC = 0.65 **High-Yield:** An FEV₁/FVC ratio of 0.65 (65%) is **below 0.70**, which is diagnostic of an **obstructive pattern**. **Mechanism in Obstructive Disease:** 1. Airway obstruction causes disproportionate reduction in FEV₁ (forced expiration is limited by airway collapse). 2. FVC may be normal or only slightly reduced (total air exhaled is less affected). 3. Result: FEV₁ falls more than FVC → ratio drops below 0.70. **Clinical Pearl:** Common obstructive diseases include COPD, asthma, and bronchiectasis. Air trapping leads to increased RV and TLC. **Mnemonic:** **OBstructive = Below 0.70** (FEV₁/FVC < 0.70)
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