Mechanisms of Hyperbaric Oxygen Chamber in Improving High Altitude–Related Diseases

1. Core Mechanism: Rapid Correction of Hypoxia

1. Significantly increases arterial partial pressure of oxygen (PaO₂)
   • At normobaric air: PaO₂ ≈ 100 mmHg; even lower at high altitude under normobaric conditions.
   • Under hyperbaric oxygen (2.0–2.5 ATA): PaO₂ can reach several hundred mmHg, far exceeding hypoxic levels at high altitude.
2. Markedly increases physically dissolved oxygen in plasma
   • Under normobaric conditions, oxygen is mainly carried by hemoglobin.
   • Under hyperbaric conditions, physically dissolved oxygen in plasma increases significantly, ensuring tissue oxygenation even when hemoglobin is saturated or oxygen-carrying capacity is reduced.
3. Expands the effective diffusion distance of oxygen

   Tissue edema and increased capillary spacing during high-altitude hypoxia limit oxygen diffusion with conventional oxygen inhalation.

   Hyperbaric oxygen increases the oxygen diffusion radius, penetrating edematous tissue and ischemic penumbras to improve cellular oxygenation.

2. Alleviation and Reversal of High-Altitude Cerebral Edema (HACE)

1. Constricts cerebral blood vessels and reduces intracranial pressure
   • Hypoxia → cerebral vasodilation → increased cerebral blood flow → cerebral edema.
   • Hyperbaric oxygen constricts cerebral blood vessels, reduces cerebral blood flow, rapidly lowering intracranial pressure and relieving vasogenic cerebral edema.
2. Improves aerobic metabolism of brain cells

   Reverses ATP depletion, Na⁺/K⁺ pump failure, and cytotoxic edema caused by hypoxia, protecting neurons.
3. Reduces blood–brain barrier disruption

   Inhibits hypoxia-induced inflammation and oxidative stress, decreasing vascular leakage.

3. Improvement and Control of High-Altitude Pulmonary Edema (HAPE)

1. Reduces hypoxic pulmonary vasoconstriction (HPV)

   Hypoxia at high altitude → intense constriction of pulmonary arterioles → pulmonary hypertension → pulmonary edema.

   Correction of hypoxia by hyperbaric oxygen relieves pulmonary vasospasm and lowers pulmonary artery pressure.
2. Reduces increased pulmonary capillary permeability

   Inhibits the release of inflammatory mediators and oxidative damage triggered by hypoxia, decreasing alveolar exudation.
3. Enhances alveolar gas exchange and oxygenation

   Even in the presence of pulmonary edema, hyperbaric oxygen maintains systemic oxygen delivery via dissolved plasma oxygen, buying time for lung repair.

4. Inhibition of Inflammation, Oxidative Stress, and Apoptosis

1. Attenuates oxidative stress injury

   Hypoxia-reperfusion readily generates large amounts of oxygen free radicals. Hyperbaric oxygen upregulates antioxidant enzymes and scavenges free radicals.
2. Suppresses inflammatory responses

   Reduces pro-inflammatory cytokines such as TNF-α and IL-6, alleviating inflammatory infiltration in the brain, lung, and systemically.
3. Decreases cellular apoptosis

   Restores mitochondrial function and reduces hypoxia-induced apoptosis of neurons and endothelial cells.

5. Improvement of Hemorheology and Microcirculation

1. Mildly reduces blood viscosity

   Decreases erythrocyte aggregation and relieves microcirculatory stasis.
2. Promotes collateral circulation

   Improves tissue perfusion, especially in patients with high-altitude heart disease or chronic mountain sickness.

6. Effects on Chronic Mountain Sickness (CMS)

• Rapidly improves tissue hypoxia and inhibits the hypoxia-inducible factor (HIF) pathway;
• Reduces excessive secretion of erythropoietin (EPO), relieving polycythemia;
• Alleviates right heart afterload and improves cardiac function.

7. Summary

1. Rapidly and potently corrects systemic and cerebral hypoxia
2. Constricts cerebral blood vessels, reduces intracranial pressure, and treats high-altitude cerebral edema
3. Lowers pulmonary artery pressure, reduces exudation, and improves high-altitude pulmonary edema
4. Inhibits the HIF pathway, inflammation, oxidative stress, and apoptosis
5. Improves microcirculation and alleviates pathological changes of chronic mountain sickness