Arteriovenous Oxygen Difference (a-v O2 Difference)
Oxygenated blood leaves the heart through arteries. As the blood circulates throughout the body, muscles extract some of that oxygen for use in energy production. The a-v O2 difference reflects the difference between the oxygen concentration in the arteries (leaving the heart) and the remaining oxygen concentration in the veins (returning to the heart).
At rest, the a-v O2 difference is typically around 5 milliliters of oxygen per deciliter (5 mL O2 / dL), representing a use coefficient of 25%. At exercise, the a-v O2 difference can increase up to around 15 mL O2 / dL with a use coefficient of 75%. In other words, more oxygen is extracted by working muscles as the intensity level increases.