Which would cause an increase in the amount of exhaled carbon dioxide?

• A. Excessive ventilation
• B. Increased cardiac output
• C. Cardiopulmonary arrest
• D. Anaerobic metabolism

Answer: (B)

An increase in exhaled CO2 occurs when more CO2 is delivered to the lungs for elimination. Cardiac output determines how much blood, carrying CO2 from tissues, reaches the lungs each minute. If cardiac output rises, more CO2-rich blood arrives at the lungs per minute, so more CO2 can be exhaled, assuming ventilation isn’t limiting.

Excessive ventilation would blow off CO2 faster, lowering the amount exhaled. Cardiopulmonary arrest stops gas exchange, so exhaled CO2 drops to near zero. Anaerobic metabolism changes the balance of CO2 production, but it doesn’t rise CO2 exhalation above normal levels. Therefore, increased cardiac output best explains an increase in exhaled CO2.