In the Fick equation, what does Q represent?

• A. Oxygen utilization
• B. Cardiac output
• C. Ventricular function
• D. Oxygen content

Answer: (B)

Q in the Fick equation represents cardiac output—the volume of blood the heart pumps per minute. The Fick principle states VO2 = Q × (CaO2 − CvO2), where CaO2 is arterial oxygen content and CvO2 is venous oxygen content. The term (CaO2 − CvO2) is the amount of oxygen extracted by the tissues, and multiplying it by the amount of blood flowing per minute (Q) gives the total oxygen consumption (VO2). Cardiac output is typically measured in liters per minute and can be calculated as heart rate times stroke volume. This distinguishes Q from oxygen utilization (VO2 itself) and from oxygen content (the amount of oxygen carried by the blood) or ventricular function (a broader aspect that influences Q but is not the variable itself).