Living high: tissue acclimatization, highland natives and chronic mountain sickness
- Regulation
- Exam priority: medium
Weeks to years at altitude change lungs, blood and muscle; people born high adapt further, and a few make too much blood (Monge disease).
Also called: High-altitude adaptation, Monge disease, Chronic mountain sickness
See it in 3D: Kidneys
What it is
Acclimatization goes on long after the first days of hyperventilation: red cell mass rises over weeks, lung diffusing capacity and tissue O₂ handling improve, and work capacity partly recovers. People born and raised at altitude (Andean, Tibetan, Ethiopian) show further, partly genetic, adaptations. When the erythropoietic response overshoots, chronic mountain sickness appears: excessive erythrocytosis, hypoxemia and pulmonary hypertension that resolve with descent. Bogotá (about 2600 m) is moderate altitude, where these changes are mild but measurable.
How it works, step by step
- Lower barometric pressure lowers inspired and alveolar PO₂; carotid bodies drive ventilation up, lowering PaCO₂.
- Renal bicarbonate loss over days corrects the alkalosis and lets ventilation rise further (ventilatory acclimatization).
- Hypoxia stabilizes HIF in the kidney; EPO rises and, over weeks, red cell mass and hemoglobin increase.
- 2,3-BPG rises in red cells, shifting the O₂ curve right and helping unloading in tissues.
- With time, lung capillary blood volume and alveolar surface (especially in those born high) raise diffusing capacity.
- Muscle capillary density rises (partly because fibres get smaller), shortening the diffusion distance for O₂.
- In susceptible people the hypoxic drive to breathe blunts with years; PaO₂ falls further, EPO stays high and the hematocrit climbs too high.
- High viscosity plus hypoxic pulmonary vasoconstriction raise pulmonary artery pressure and load the right ventricle.
Oxygen–hemoglobin dissociation curve
P50 27.7 mmHgArterial blood 97 %Mixed venous blood 73 %O₂ given up to the tissues 24 %
Right shift (P50 27.7 mmHg): Hb has less affinity and gives up more O₂ in the tissues. Acid, CO₂, heat and 2,3-BPG cause it.
- Current curve
- Normal curve (pH 7.40 · 37 °C)
- Arterial blood (PO₂ 100)
- Mixed venous blood (PO₂ 40)
- O₂ given up to the tissues
Approximate values at Bogotá-like altitude (~2600 m) versus sea level, healthy adult residents (ranges; local norms vary)
| Parameter | Value | Note |
|---|---|---|
| Barometric pressure | ≈ 550–570 mmHg | ≈ 760 mmHg at sea level |
| Inspired PO₂ | ≈ 105–110 mmHg | ≈ 150 mmHg at sea level |
| Arterial PO₂ | ≈ 60–75 mmHg | ≈ 80–100 mmHg at sea level |
| Arterial PCO₂ | ≈ 29–35 mmHg | ≈ 35–45 mmHg at sea level |
| SpO₂ at rest | ≈ 90–96% | ≈ 95–100% at sea level |
| Hemoglobin | roughly 0.5–1.5 g/dL above sea-level ranges | use altitude-adjusted ranges |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Acclimatized lowlander versus lifelong highlanders (general tendencies)
| Feature | Acclimatized lowlander | Andean native | Tibetan native |
|---|---|---|---|
| Resting ventilation | High | Near or slightly above sea-level values (blunted hypoxic drive) | High, with a brisk hypoxic response |
| Hemoglobin | Rises over weeks | Highest | Close to sea-level values |
| Chest and lung volumes | Unchanged | Larger | Larger |
| Pulmonary artery pressure | Mildly raised | Often raised | Near normal (more nitric oxide) |
| Chronic mountain sickness | Rare | Most frequent | Uncommon |
Clinical notes
- Chronic mountain sickness: headache, dizziness, poor sleep, cyanosis, plethora and dilated veins; scored with the Qinghai criteria; relieved by moving to low altitude.
- Long-standing high-altitude pulmonary hypertension can lead to right heart failure (cor pulmonale); COPD and sleep apnea at altitude add to the hypoxemia.
- An erythrocytosis in a highland resident is first read against local norms; very high values or a low EPO suggest another cause, such as polycythemia vera.
Test yourself
Think of the answer, then tap the question to see it.
Which change of acclimatization takes the longest to develop: hyperventilation, renal bicarbonate loss, or a rise in red cell mass?
The rise in red cell mass. Ventilation rises within hours, bicarbonate falls over days, but EPO-driven red cell production needs weeks to months to raise red cell mass.
How do Tibetan highlanders typically differ from Andean highlanders in hemoglobin and disease risk?
Tibetans keep hemoglobin close to sea-level values and rely on higher ventilation and blood flow; Andeans have higher hemoglobin and more chronic mountain sickness.
What three features define chronic mountain sickness?
Excessive erythrocytosis, marked hypoxemia and, often, pulmonary hypertension, in a long-term high-altitude resident; the features regress after descent.
Why might a healthy adult from Bogotá have a hemoglobin flagged as high by a sea-level reference range?
At about 2600 m the lower inspired PO₂ raises EPO and red cell mass a little; hemoglobin must be interpreted with altitude-adjusted ranges.
Connections
See it in 3D1
The structures of Durgical's 3D anatomy where it happens.
In Biochemistry1
In Pharmacology1
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: Chronic Mountain Sickness: Clinical Aspects, Etiology, Management, and Treatment (High Altitude Medicine & Biology (PMC), 2016); Human adaptation to high‐altitude: A contemporary comparison of the oxygen cascade in Andean, Tibetan and Ethiopian highlanders (Experimental Physiology (PMC), 2026); High-Altitude Travel and Altitude Illness (CDC Yellow Book, 2025); Acute mountain sickness: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2024).
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Representative model, for educational purposes only.