🏥 USMLE Exam Prep

Which of the following is the primary mechanism by which carbon monoxide poisoning leads to hypoxia?

A Inhibition of cytochrome c oxidase
B Decreased partial pressure of oxygen (PO2) in arterial blood
C Reduced oxygen-carrying capacity of hemoglobin and leftward shift of the oxygen dissociation curve
D Direct damage to lung parenchyma, impairing gas exchange

✓ Correct Answer: Option C

Carbon monoxide has a much higher affinity for hemoglobin than oxygen, forming carboxyhemoglobin (COHb), which reduces the blood's oxygen-carrying capacity. It also causes a leftward shift of the oxygen dissociation curve, impairing oxygen release to tissues.

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