Oxygenation at different altitudes

Increasing altitude results in a decrease in inspired oxygen (PiO₂), arterial oxygen₂ (PaO₂), and arterial oxygen saturation (SaO₂). Note that the difference between PiO₂ and PaO₂ narrows at high altitudes because of increased ventilation, and that SaO₂ is well maintained while awake until over 3000 meters.