A mountaineer ascends to 4500 m above sea level. After 2 weeks of acclimatization, which physiological adaptation is expected to persist?

• A Acute hyperventilation-induced respiratory alkalosis is still present unchanged
• B Increased erythropoietin-driven polycythemia with increased 2,3-DPG in red cells ✓
• C Decreased heart rate due to parasympathetic dominance
• D Decreased tidal volume to conserve energy

Explanation

Chronic altitude acclimatization produces several sustained changes: (1) polycythemia driven by EPO from peritubular fibroblasts in response to hypoxia-inducible factor-1 (HIF-1α), increasing O2-carrying capacity; (2) increased erythrocyte 2,3-DPG that shifts the O2-Hb curve rightward, aiding O2 delivery to tissues; (3) renal HCO3- excretion compensates the initial respiratory alkalosis (pH normalizes over days). The initial hyperventilation persists but is partially compensated. Heart rate remains elevated in early acclimatization.

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

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