What is the relationship between cabin altitude and arterial oxygen tension in a healthy person breathing room air?

What is the relationship between cabin altitude and arterial oxygen tension in a healthy person breathing room air?

• A. Higher cabin altitude reduces arterial oxygen tension.
• B. Higher cabin altitude increases arterial oxygen tension.
• C. Cabin altitude has no effect on arterial oxygen tension.
• D. Arterial oxygen tension depends only on ventilation rate, not altitude.

Answer: (D)

As cabin altitude rises, the barometric pressure falls. Even though the mix of gases you breathe remains about 21% oxygen, the lower ambient pressure decreases the partial pressure of inspired oxygen, which lowers the alveolar oxygen tension and, consequently, the arterial oxygen tension. The body can increase ventilation to raise PaO2 somewhat, but the reduced inspired O2 at altitude sets a lower limit for PaO2. Therefore, higher cabin altitude reduces arterial oxygen tension. The idea that arterial O2 tension depends only on ventilation rate ignores the reduced oxygen availability with altitude and isn’t correct.

As cabin altitude rises, the barometric pressure falls. Even though the mix of gases you breathe remains about 21% oxygen, the lower ambient pressure decreases the partial pressure of inspired oxygen, which lowers the alveolar oxygen tension and, consequently, the arterial oxygen tension. The body can increase ventilation to raise PaO2 somewhat, but the reduced inspired O2 at altitude sets a lower limit for PaO2. Therefore, higher cabin altitude reduces arterial oxygen tension. The idea that arterial O2 tension depends only on ventilation rate ignores the reduced oxygen availability with altitude and isn’t correct.