What is the correct formula for the arterial-venous oxygen content difference?

What is the correct formula for the arterial-venous oxygen content difference?

• A. C(a-v)O2 = CaO2 - CvO2
• B. CaO2 - CvO2
• C. CaO2 + CvO2
• D. CvO2 - CaO2

Answer: (A)

The arterial-venous oxygen content difference represents how much oxygen tissues extract from the circulating blood. It’s found by subtracting the venous oxygen content from the arterial oxygen content, so the correct expression is CaO2 − CvO2. This value increases when tissues take up more oxygen (as with exercise) and decreases when delivery exceeds demand. CaO2 and CvO2 themselves are determined by the amount of oxygen bound to hemoglobin plus the dissolved oxygen in plasma, with CaO2 = (Hb × 1.34 × SaO2) + (0.003 × PaO2) and CvO2 = (Hb × 1.34 × SvO2) + (0.003 × PvO2). Adding the values or reversing the order would not reflect tissue oxygen extraction.

The arterial-venous oxygen content difference represents how much oxygen tissues extract from the circulating blood. It’s found by subtracting the venous oxygen content from the arterial oxygen content, so the correct expression is CaO2 − CvO2. This value increases when tissues take up more oxygen (as with exercise) and decreases when delivery exceeds demand. CaO2 and CvO2 themselves are determined by the amount of oxygen bound to hemoglobin plus the dissolved oxygen in plasma, with CaO2 = (Hb × 1.34 × SaO2) + (0.003 × PaO2) and CvO2 = (Hb × 1.34 × SvO2) + (0.003 × PvO2). Adding the values or reversing the order would not reflect tissue oxygen extraction.