At high altitude (>3500 m), a climber acclimatizes over days. A key feature of acclimatization is the rightward shift of the oxyhemoglobin dissociation curve, facilitating oxygen unloading in tissues. This rightward shift occurs primarily because:

• A Altitude-induced respiratory alkalosis directly causes a Bohr effect rightward shift by raising blood pH
• B Altitude-induced hypoxia stimulates red blood cell 2,3-BPG synthesis via activation of bisphosphoglycerate mutase, which binds beta-chains of deoxyhemoglobin and reduces O2 affinity ✓
• C Hypoxia-induced polycythemia increases hematocrit, reducing the partial pressure needed to load hemoglobin
• D Metabolic acidosis from anaerobic glycolysis at altitude reduces blood pH, shifting the curve rightward

Explanation

Within hours of arriving at altitude, erythrocyte 2,3-bisphosphoglycerate (2,3-BPG) synthesis increases via activation of the bisphosphoglycerate mutase pathway (a shunt in glycolysis). 2,3-BPG preferentially binds to the central cavity of deoxyhemoglobin (T-state), stabilizing it and reducing O2 affinity, shifting the dissociation curve rightward (increased P50). This facilitates O2 unloading in peripheral tissues at altitude. Note that the concurrent respiratory alkalosis from hyperventilation initially shifts the curve leftward (Bohr effect), partially opposing the 2,3-BPG effect until the kidneys compensate the alkalosis over 2-3 days.

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

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Written and medically reviewed by the StethoPrep medical team.