Which expression correctly represents VO2 using the Fick equation?

Which expression correctly represents VO2 using the Fick equation?

• A. VO2 = CO × CaO2
• B. VO2 = CO × (CaO2 − CvO2)
• C. VO2 = HR × SV
• D. VO2 = CO ÷ (CaO2 − CvO2)

Answer: (B)

The Fick principle links oxygen use to both blood flow and how much oxygen is extracted from each unit of blood. VO2 represents the amount of oxygen consumed each minute, which depends on how much oxygen-rich blood arrives (cardiac output, CO) and how much of that oxygen is removed by tissues. The key is the arteriovenous oxygen content difference, CaO2 − CvO2, which represents the oxygen extracted from the blood. Multiply this extraction per unit of blood by the total blood flow to get the total oxygen consumption: VO2 = CO × (CaO2 − CvO2). Writing VO2 as CO × CaO2 would ignore tissue extraction, and dividing by the difference would invert the relationship. HR × SV is another way to express CO, but the essential Fick form requires the arteriovenous oxygen content difference to reflect how much oxygen is actually used by tissues.

The Fick principle links oxygen use to both blood flow and how much oxygen is extracted from each unit of blood. VO2 represents the amount of oxygen consumed each minute, which depends on how much oxygen-rich blood arrives (cardiac output, CO) and how much of that oxygen is removed by tissues. The key is the arteriovenous oxygen content difference, CaO2 − CvO2, which represents the oxygen extracted from the blood. Multiply this extraction per unit of blood by the total blood flow to get the total oxygen consumption: VO2 = CO × (CaO2 − CvO2). Writing VO2 as CO × CaO2 would ignore tissue extraction, and dividing by the difference would invert the relationship. HR × SV is another way to express CO, but the essential Fick form requires the arteriovenous oxygen content difference to reflect how much oxygen is actually used by tissues.