Which pair represents the alveolar partial pressures of oxygen and carbon dioxide?

Which pair represents the alveolar partial pressures of oxygen and carbon dioxide?

• A. 90, 50
• B. 70, 28
• C. 88, 30
• D. 104, 40

Answer: (D)

Alveolar gas has a high O2 content and a CO2 level near 40 mmHg because oxygen diffuses into the blood while carbon dioxide diffuses out into the alveoli to be exhaled. In a healthy person at sea level, the alveolar PO2 is about 100 mmHg and the alveolar PCO2 is about 40 mmHg. The pair that shows O2 around 100 and CO2 around 40 best fits these values, which is why 104 mmHg for oxygen and 40 mmHg for carbon dioxide is the correct match. The other options either show an O2 value far from the expected ~100 or a CO2 value far from ~40, making them inconsistent with typical alveolar gas.

Alveolar gas has a high O2 content and a CO2 level near 40 mmHg because oxygen diffuses into the blood while carbon dioxide diffuses out into the alveoli to be exhaled. In a healthy person at sea level, the alveolar PO2 is about 100 mmHg and the alveolar PCO2 is about 40 mmHg. The pair that shows O2 around 100 and CO2 around 40 best fits these values, which is why 104 mmHg for oxygen and 40 mmHg for carbon dioxide is the correct match. The other options either show an O2 value far from the expected ~100 or a CO2 value far from ~40, making them inconsistent with typical alveolar gas.