## Investigation of Choice for COPD Diagnosis and Airflow Pattern **Key Point:** Spirometry is the gold standard investigation for diagnosing COPD and identifying the obstructive pattern of airflow limitation. ### Why Spirometry is the Investigation of Choice Spirometry directly measures: - **FEV₁/FVC ratio** — the hallmark of obstructive pattern (< 0.70 post-bronchodilator confirms COPD) - **FEV₁** — severity grading (GOLD classification) - **Bronchodilator response** — helps differentiate COPD from asthma (< 12% and < 200 mL improvement in COPD) ### Spirometry Pattern in COPD | Parameter | COPD Pattern | Normal | |-----------|--------------|--------| | FEV₁/FVC | < 0.70 | ≥ 0.75 | | FEV₁ | Reduced | Normal | | FVC | Normal or reduced | Normal | | Flow-volume loop | Scooped expiratory curve | Normal | **High-Yield:** The FEV₁/FVC ratio < 0.70 is the diagnostic criterion for airflow obstruction (GOLD 2023). This ratio is independent of predicted values and age, making it the most reliable single parameter. **Clinical Pearl:** In COPD, the expiratory flow limitation occurs due to dynamic airway compression during forced expiration, resulting in the characteristic "scooped" or concave expiratory limb on the flow-volume loop. ### Role of Bronchodilator Testing Bronchodilator response (short-acting beta-2 agonist) helps: - Confirm fixed airflow obstruction (minimal reversibility in COPD vs. significant in asthma) - Establish baseline for monitoring disease progression - Guide therapeutic decisions [cite:Harrison 21e Ch 297]
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