Theory 05/Altitude & Hypoxia Physiology
Mountain Sickness Is a Balance
The claim
Acute mountain sickness is set by the ratio of ventilatory response to fluid flux into the brain rather than by oxygen saturation, so two people at the same saturation can differ in symptoms.
01The mechanism
Hypoxia raises cerebral blood flow and capillary pressure, which drives fluid flux. A strong ventilatory response lowers carbon dioxide and reduces that flux, so the two oppose each other.
Symptoms appear when flux outruns clearance, which is a ratio rather than a saturation level.
02What this is not
Saturation-threshold models
Those use oxygen saturation. This uses the balance of flux and clearance, which explains discordance between saturation and symptoms.
03Predictions
- P1Symptoms should track the ratio better than saturation.
- P2Ventilatory stimulants should reduce symptoms at constant saturation.
04Refutation
Symptoms tracking saturation at controlled flux would favour the threshold model.