In spirometry, which of the following patterns is characterized by a reduced FEV₁/FVC ratio (<70%) with normal total lung capacity (TLC)?

Explanation

## Obstructive vs Restrictive Spirometry Patterns **Key Point:** The FEV₁/FVC ratio is the primary discriminator between obstructive and restrictive airway disease. A ratio <70% (or <0.70) is pathognomonic for obstruction. ### Pattern Recognition | Feature | Obstructive | Restrictive | Mixed | |---------|-------------|-------------|-------| | **FEV₁/FVC** | <70% ↓ | >70% (normal or ↑) | <70% ↓ | | **FEV₁** | ↓↓ | ↓ | ↓↓ | | **FVC** | Normal or ↓ | ↓ | ↓ | | **TLC** | ↑ | ↓ | ↓ | | **RV** | ↑↑ | Normal or ↓ | ↑ | | **Examples** | COPD, asthma | ILD, chest wall disease | COPD + ILD | **High-Yield:** In obstructive disease, air trapping causes **residual volume (RV) to increase disproportionately**, but TLC may be normal or only mildly reduced early. The FEV₁/FVC ratio falls because FEV₁ drops faster than FVC. **Clinical Pearl:** A reduced FEV₁/FVC with normal TLC is the hallmark of **pure obstruction without restriction** — typical of early COPD or asthma without parenchymal involvement. ### Why This Ratio Matters FEV₁/FVC reflects the **speed of airway emptying**. In obstruction, airways collapse during forced expiration, trapping air and reducing the fraction of FVC that exits in the first second. In restriction, both FEV₁ and FVC fall proportionally, so the ratio stays normal or even rises. [cite:Harrison 21e Ch 246]