How much oxygen do we keep after exhalation?

How much oxygen do we keep after exhalation?

• A. 21%
• B. 16%
• C. 5%
• D. 0%

Answer: (C)

Oxygen in the air you inhale is about 21%. As your lungs exchange gases, your tissues use some of that oxygen, so the air you exhale has less oxygen. In normal breathing, expired air contains roughly 16% oxygen. That means you don’t keep all the oxygen you inhale, but you don’t drop to zero either—the rest of the difference is what the tissues consumed, and the exhaled air also carries a small amount of carbon dioxide. So the amount of oxygen left after exhalation is about 16%, not the full 21%, and not 0% or as low as 5% in healthy breathing.

Oxygen in the air you inhale is about 21%. As your lungs exchange gases, your tissues use some of that oxygen, so the air you exhale has less oxygen. In normal breathing, expired air contains roughly 16% oxygen. That means you don’t keep all the oxygen you inhale, but you don’t drop to zero either—the rest of the difference is what the tissues consumed, and the exhaled air also carries a small amount of carbon dioxide. So the amount of oxygen left after exhalation is about 16%, not the full 21%, and not 0% or as low as 5% in healthy breathing.