A 68-year-old man with COPD has FEV1 = 1.2 L, FVC = 2.8 L, FEV1/FVC = 43%, RV = 4.2 L, TLC = 8.0 L, DLCO reduced to 45% predicted. Which pattern is present, and which finding best distinguishes emphysema from chronic bronchitis in this context?

• A Restrictive pattern; reduced DLCO indicates interstitial involvement
• B Obstructive pattern; normal DLCO would favour chronic bronchitis over emphysema
• C Mixed obstructive-restrictive pattern; reduced TLC confirms restriction
• D Obstructive pattern; hyperinflation (RV/TLC ratio elevated) with reduced DLCO indicates emphysema with parenchymal destruction ✓

Explanation

FEV1/FVC < 70% (here 43%) with normal or increased TLC confirms obstruction. TLC of 8.0 L and RV of 4.2 L (RV/TLC = 53%, normal <35%) indicate air trapping and hyperinflation. The markedly reduced DLCO (diffusing capacity for CO) is the key distinguishing feature of emphysema: alveolar destruction reduces membrane surface area for gas exchange. In pure chronic bronchitis, DLCO is typically normal or only mildly reduced because alveolar architecture is preserved. This combination — obstruction + hyperinflation + reduced DLCO — defines emphysema physiologically.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.