Using the Fick principle, if the arterial-venous oxygen content difference increases while oxygen consumption remains constant, what happens to calculated cardiac output?

Using the Fick principle, if the arterial-venous oxygen content difference increases while oxygen consumption remains constant, what happens to calculated cardiac output?

• A. Cardiac output increases
• B. Cardiac output decreases
• C. Cardiac output remains unchanged
• D. Cardiac output doubles

Answer: (B)

Using the Fick principle, VO2 equals CO times the arterial–venous O2 content difference (VO2 = CO × (CaO2 − CvO2)). If the oxygen consumption stays the same but the arteriovenous oxygen difference increases, the same VO2 must be achieved with a smaller CO. More O2 is being extracted per unit of blood, so less blood flow is required to meet the metabolic demand. Hence, calculated cardiac output decreases.

Using the Fick principle, VO2 equals CO times the arterial–venous O2 content difference (VO2 = CO × (CaO2 − CvO2)). If the oxygen consumption stays the same but the arteriovenous oxygen difference increases, the same VO2 must be achieved with a smaller CO. More O2 is being extracted per unit of blood, so less blood flow is required to meet the metabolic demand. Hence, calculated cardiac output decreases.