Why does a chronic smoker with elevated carboxyhemoglobin levels experience impaired oxygen delivery to tissues during exercise, even if their hemoglobin concentration is normal?

💡 Explanation

Elevated carboxyhemoglobin impairs oxygen delivery because carbon monoxide (CO) outcompetes oxygen for hemoglobin binding sites, hindering the cooperative binding of oxygen. This reduces the amount of oxygen hemoglobin can carry; therefore, tissues receive less oxygen during exercise, rather than oxygen unloading being enhanced by BPG or vasodilation being prevented by nitric oxide.

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