At high altitude (above 4500 m), chronic acclimatization includes a decrease in the hypoxic ventilatory response (HVR) relative to the acute response. This 'ventilatory acclimatization' results from:

• A Carotid body desensitizes to hypoxia over days through reduced dopamine receptor expression, permanently reducing peripheral chemoreceptor sensitivity
• B Increased RBC 2,3-DPG at altitude improves tissue O₂ delivery, reducing the hypoxic stimulus to peripheral chemoreceptors
• C Cerebral vasodilation from hypoxia reduces CO₂ washout from CSF, increasing local CO₂ and acidifying CSF to stimulate central chemoreceptors
• D Renal excretion of bicarbonate corrects the respiratory alkalosis caused by hyperventilation, restoring CSF pH and removing the central chemoreceptor inhibition that was blunting HVR ✓

Explanation

On arrival at altitude, hypoxia stimulates peripheral chemoreceptors (carotid body) to increase ventilation. This hyperventilation causes respiratory alkalosis (elevated pH, low PaCO₂). The alkalotic CSF inhibits central chemoreceptors, partially limiting the full HVR. Over 2–5 days, the kidneys compensate by excreting HCO₃⁻, normalizing blood and CSF pH. As the alkalosis resolves, the central chemoreceptor inhibition is lifted, allowing the peripheral hypoxic drive to express more fully — this is 'ventilatory acclimatization' (a progressive increase in minute ventilation over days). It also explains why acetazolamide (carbonic anhydrase inhibitor) accelerates acclimatization by inducing a metabolic acidosis that counters the respiratory alkalosis.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.