If a pulmonary embolism blocks blood flow to a portion of the lung, what distinguishes the observed hypoxemia from hypoxemia due to high altitude?

💡 Explanation

A pulmonary embolism increases the alveolar-arterial (A-a) gradient because it prevents blood from reaching ventilated alveoli, impairing diffusion. Therefore, the A-a gradient increases, rather than remaining normal as in high altitude, because the embolism creates a ventilation-perfusion mismatch.

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