Causes of Carbon Dioxide Retention in Lung Disease

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Abstract
Carbon dioxide retention in chronic lung disease is often attributed to "alveolar hypoventilation." This designation is misleading because the patients are usually moving abnormally large amounts of air into their alveoli, and it diverts attention from the real cause: ventilation-perfusion inequality. Recent work using lung models shows that this mechanism can interfere dramatically with carbon dioxide elimination. Indeed, pure uncompensated ventilation-perfusion inequality often impairs carbon dioxide output almost as much as oxygen uptake. Carbon dioxide retention is particularly likely to occur when one lung region inspires gas from another, as in centrilobular emphysema. Treatment should be directed at the cause of the ventilation-perfusion inequality as well as at increasing the amount of air moving into the alveoli.