A 58-year-old male smoker presents to the chest clinic with progressive dyspnea on exertion and chronic cough productive of scanty sputum for the past 3 years. On examination, he has reduced breath sounds bilaterally and prolonged expiration. Spirometry shows: FEV₁ = 52% predicted, FVC = 78% predicted, FEV₁/FVC ratio = 0.58. DLCO is reduced at 65% predicted. What is the most likely diagnosis?

Explanation

## Spirometric Pattern Analysis **Key Point:** The FEV₁/FVC ratio of 0.58 (< 0.70) is the hallmark of obstructive airway disease. The reduced DLCO (65%) indicates alveolar destruction, consistent with emphysema. ### Interpretation of Findings | Parameter | Value | Interpretation | |-----------|-------|----------------| | FEV₁ | 52% predicted | Moderately reduced | | FVC | 78% predicted | Mildly reduced | | FEV₁/FVC | 0.58 | **Obstructive pattern (< 0.70)** | | DLCO | 65% predicted | Reduced (emphysema marker) | **High-Yield:** In obstructive diseases, FEV₁/FVC is reduced because airway collapse during forced expiration traps air. The reduced DLCO specifically points to emphysema (loss of alveolar-capillary surface area) rather than simple bronchitis. ### Why This Pattern Indicates Emphysema 1. **Obstructive physiology**: FEV₁/FVC < 0.70 confirms airway obstruction 2. **Reduced DLCO**: Indicates parenchymal destruction and loss of gas exchange surface 3. **Clinical context**: Smoking history, prolonged expiration, and reduced breath sounds support COPD with emphysematous component 4. **FVC mildly reduced**: Occurs in emphysema due to air trapping and loss of elastic recoil **Clinical Pearl:** Emphysema is the only obstructive disease with significantly reduced DLCO. Chronic bronchitis alone would show normal DLCO. This distinction is critical for prognosis and management. **Mnemonic: OBSTRUCTIVE pattern = FEV₁/FVC < 0.70** — remember this ratio is the gatekeeper for obstructive vs. restrictive classification.