## Obstructive Pattern on Spirometry **Key Point:** An FEV₁/FVC ratio <0.70 (or <70%) with reduced FEV₁ defines an obstructive defect. The most common cause of obstructive airway disease in India remains COPD, particularly in smokers and those with occupational/biomass exposure. ### Epidemiology of Obstructive Diseases in India | Disease | Prevalence | Risk Factors | FEV₁/FVC | |---------|-----------|--------------|----------| | COPD | ~4–5% adult population | Smoking, biomass fuel, occupational | <0.70 | | Asthma | ~2–3% | Atopy, allergen exposure, genetics | <0.70 (variable) | | Bronchiectasis | Lower prevalence | Post-infection, CF, immunodeficiency | <0.70 | | ILD | Lower prevalence | Occupational, autoimmune | Normal/high | **High-Yield:** COPD is the leading cause of obstructive spirometry in adult smokers. The combination of smoking history + obstructive pattern + normal FVC makes COPD the most common diagnosis. **Clinical Pearl:** ILD typically presents with a restrictive pattern (reduced FVC, normal or elevated FEV₁/FVC), not obstructive, so it can be excluded immediately. ### Why This Pattern Indicates COPD 1. **Reduced FEV₁** = airflow obstruction (small airways collapse during forced expiration) 2. **Normal FVC** = total lung capacity preserved (no restriction) 3. **FEV₁/FVC <0.70** = diagnostic hallmark of obstruction 4. **Smoking history** = strongest risk factor for COPD in this demographic **Mnemonic:** **COPD = Chronic Obstructive Pulmonary Disease** — the most frequent cause of obstructive spirometry in smokers and elderly patients in India.
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