Control of respiration · Physiology

Why does a patient with severe carbon monoxide (CO) poisoning often fail to show an increase in ventilation despite critically low oxygen delivery to tissues?

  1. CO directly inhibits the medullary respiratory centres and depresses their drive
  2. Arterial PO2 remains normal, so peripheral chemoreceptors are not stimulated
  3. CO binds to and inactivates the central chemoreceptors within the medulla oblongata
  4. The carotid bodies are unable to detect oxygen while any CO is present
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Correct answer: Arterial PO2 remains normal, so peripheral chemoreceptors are not stimulated

Peripheral chemoreceptors respond to the partial pressure of dissolved oxygen (PO2), not the total oxygen content or hemoglobin saturation. In CO poisoning, PO2 remains normal while oxygen content is low, so the 'hypoxic drive' is never triggered.

Difficulty: Medium Question 27 of 40

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