What does the arteriovenous difference represent?

• A. Difference between oxygen content of arterial blood and mixed venous blood
• B. Difference between oxygen content of arterial blood and venous oxygen saturation
• C. Difference between oxygen content of alveolar air and arterial blood
• D. Difference between oxygen content of arterial blood and capillary blood

Answer: (A)

The arteriovenous difference shows how much oxygen the tissues extract from the blood as it passes through the systemic circulation. It’s the difference in oxygen content between arterial blood (oxygen carried from the lungs) and mixed venous blood (oxygen remaining after tissue extraction returning to the heart). Practically, it equals CaO2 minus CvO2, where CaO2 is the oxygen content of arterial blood and CvO2 is the oxygen content of mixed venous blood. This value rises when tissues demand more oxygen (like during exercise) or when delivery is reduced relative to demand, reflecting the extent of peripheral oxygen extraction. Since it’s based on content, not just saturation, it accounts for how much oxygen is bound to hemoglobin as well as dissolved oxygen.