A trained endurance athlete performs maximal exercise. Compared with an untrained person, which diffusing capacity (DLCO) change is expected?

• A DLCO is lower in the athlete because of reduced alveolar membrane surface area
• B DLCO is lower in the athlete because of exercise-induced pulmonary edema
• C DLCO is identical in both because diffusing capacity is fixed by alveolar membrane anatomy
• D DLCO is higher in the athlete because of greater pulmonary capillary blood volume and recruitment ✓

Explanation

Endurance training increases pulmonary capillary blood volume and recruits more capillaries during exercise, raising DLCO. This adaptation improves gas exchange at maximal cardiac outputs. The fixed-anatomy option ignores the recruitable pulmonary vascular bed. Exercise-induced edema occurs only in some elite athletes and is not the typical training adaptation.

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

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