Oxygen extraction ratio (O2ER) is defined as which expression?

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Multiple Choice

Oxygen extraction ratio (O2ER) is defined as which expression?

Oxygen extraction ratio tells us what fraction of the oxygen delivered by the arterial blood is actually taken up by the tissues. It comes from the Fick principle: oxygen consumption (VO2) equals cardiac output (CO) times the difference between arterial and venous oxygen content, and oxygen delivery (DO2) equals CO times arterial oxygen content. So O2ER = VO2/DO2 simplifies to (CaO2 − CvO2) / CaO2. This uses arterial oxygen content in the denominator and the difference between arterial and mixed venous oxygen content in the numerator, yielding a value between 0 and 1 that reflects extraction efficiency. Using the venous content in the denominator or reversing the subtraction would not correctly represent the amount delivered versus what’s extracted.

Oxygen extraction ratio tells us what fraction of the oxygen delivered by the arterial blood is actually taken up by the tissues. It comes from the Fick principle: oxygen consumption (VO2) equals cardiac output (CO) times the difference between arterial and venous oxygen content, and oxygen delivery (DO2) equals CO times arterial oxygen content. So O2ER = VO2/DO2 simplifies to (CaO2 − CvO2) / CaO2. This uses arterial oxygen content in the denominator and the difference between arterial and mixed venous oxygen content in the numerator, yielding a value between 0 and 1 that reflects extraction efficiency. Using the venous content in the denominator or reversing the subtraction would not correctly represent the amount delivered versus what’s extracted.

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