## Obstructive Pattern Recognition **Key Point:** An FEV₁/FVC ratio <0.70 defines airflow obstruction. In a smoker with progressive dyspnea and normal TLC, COPD is the most common diagnosis. ### Why COPD is Most Common **High-Yield:** COPD prevalence in smokers with >20 pack-years is 15–20%, making it far more frequent than other obstructive conditions in this demographic. **Clinical Pearl:** The combination of: - Smoking history (major risk factor) - Progressive dyspnea (typical COPD trajectory) - Reduced FEV₁/FVC (hallmark of obstruction) - Normal TLC (rules out restrictive disease) ...points strongly to COPD as the diagnosis. ### Differential Obstructive Patterns | Condition | FEV₁/FVC | TLC | Key Feature | |-----------|----------|-----|-------------| | COPD | <0.70 | Normal or ↑ | Smoking history, progressive | | Asthma | <0.70 | Normal | Reversibility, episodic | | Bronchiectasis | <0.70 | Normal | Recurrent infections, sputum | | Tracheal stenosis | <0.70 | Normal | Fixed obstruction, stridor | **Mnemonic: COAT** — Common Obstructive Airway Triad in smokers = **C**OPD, **O**bstruction, **A**irflow, **T**obacco. **Warning:** Do not assume asthma without evidence of reversibility (bronchodilator response ≥12% and ≥200 mL FEV₁ improvement). Asthma is less common in this age group with pure smoking exposure and no mention of atopy or reversibility. [cite:Harrison 21e Ch 297]
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