Question

Direct Fick method of measuring cardiac output requires estimation of:

• A. O2 content of arterial blood
• B. O2 consumption per unit time
• C. Arteriovenous O2 difference
• D. All of the above

Hint:

Cardiac output = O2 consumption / A-V O2 difference, so every listed quantity is needed.

Answer 1

The Correct Option is D

Step 1: The Fick principle states that the amount of a substance taken up by an organ (or by the whole body) per unit time equals the blood flow multiplied by the arteriovenous concentration difference of that substance. Rearranged for the lungs and oxygen, cardiac output equals oxygen consumption per unit time divided by the arteriovenous oxygen difference.

Step 2: So the formula is \[ CO = \frac{O_2\ consumption\ per\ minute}{Arterial\ O_2 - Venous\ O_2} \] To compute this you must know oxygen consumption per unit time (numerator) and the A-V oxygen difference (denominator).

Step 3: The A-V difference itself needs the O2 content of arterial blood and the O2 content of mixed venous blood (sampled from the pulmonary artery). Therefore arterial O2 content, O2 consumption per unit time, and the arteriovenous O2 difference are all required.

Step 4: Since every listed item is needed, the correct answer is All of the above. Picking any single option alone is incomplete because none by itself lets you solve the equation.