## Obstructive Spirometry Pattern Recognition **Key Point:** An FEV₁/FVC ratio <0.70 with reduced FEV₁ defines airflow obstruction. The most common cause of chronic obstructive spirometry in India is COPD, particularly in smokers and those exposed to biomass fuel. **High-Yield:** COPD prevalence in India is ~5% overall but significantly higher in smokers and rural populations with indoor air pollution exposure. The classic triad: smoking history + obstructive pattern + normal TLC. ### Why COPD is the Answer | Feature | COPD | Asthma | Bronchiectasis | ILD | |---------|------|--------|---|---| | **FEV₁/FVC** | <0.70 (fixed) | <0.70 (variable) | <0.70 | >0.70 | | **TLC** | Normal or ↑ | Normal | Normal | ↓ | | **Reversibility** | Minimal | Yes (>12% improvement) | Minimal | No | | **Age of onset** | >40 years | Any age | Variable | Variable | | **Smoking history** | Typical | Not required | Not required | Occupational/idiopathic | **Clinical Pearl:** In this patient, the normal TLC rules out emphysema-dominant disease with hyperinflation, but COPD (particularly chronic bronchitis phenotype) remains the most common diagnosis in a 52-year-old smoker with fixed obstruction. **Mnemonic: COPD Features — "ABCD"** - **A**irflow obstruction (FEV₁/FVC <0.70) - **B**ronchitis or emphysema (pathology) - **C**hronic and progressive - **D**ysfunction (functional impairment) [cite:Harrison 21e Ch 314]
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