Reach a lower inspired oxygen pressure by lowering the whole atmosphere at altitude, or by lowering the oxygen fraction in a normobaric hypoxia system.
Choose the gas location
This is Dalton's law in the environment: oxygen fraction multiplied by total barometric pressure.
Hypobaric hypoxia
Actual altitude
Barometric pressure
560 mmHg
Oxygen fraction
20.9%
Inspired oxygen pressure
117.1 mmHg
Oxygen remains 20.9% of dry air. Altitude lowers barometric pressure, so every gas has less partial pressure.
Normobaric hypoxia
Hypoxico-style system
Barometric pressure
760 mmHg
Oxygen fraction
15.4%
Inspired oxygen pressure
117.0 mmHg
Target: 15.4% FIO2
Total room pressure stays near ambient. The system lowers the oxygen fraction in the gas delivered to the room, tent, or mask.
Inspired oxygen pressures match
The two conditions match within 1 mmHg in this dry-gas comparison.
Same outcome, different control variable
117.1 mmHg
Actual altitude
117.0 mmHg
Normobaric system
Actual altitude changes pressure
PO₂ = 0.209 × PB
20.9% × 560 = 117.1 mmHg
Normobaric hypoxia changes fraction
PO₂ = FIO₂ × PB
15.4% × 760 = 117.0 mmHg
Where does arterial PaO2 come in?
These calculations stop at inspired gas. Alveolar PAO2 also depends on carbon dioxide and respiratory quotient; arterial PaO2 additionally depends on gas exchange and the alveolar-arterial gradient. Those are the next model layers for Chapter 12.
Next: oxygen binding in blood
Inspired oxygen pressure establishes the upstream condition. Continue by seeing how blood PO2 and tissue conditions determine hemoglobin saturation.
This teaching model combines Dalton's law with the International Standard Atmosphere pressure approximation through 11 km. It is algebraic: there is no numerical solver and no prediction of an individual's oxygen saturation or symptoms.
Chapter 11: Respiration introduces partial pressure as gas fraction multiplied by total pressure.
JSim EBTOW oxygen and water exchange model provides a downstream conceptual reference for partial-pressure-driven oxygen transport, hemoglobin binding, and tissue consumption. It does not validate altitude or ventilation.