Labs / Biology
Alveolar Gas Exchange
A single air sac sits above a capillary of flowing red blood cells. Oxygen and carbon dioxide slip across the thin membrane between them, each moving from where its pressure is high to where it is low. Change how you breathe, climb to altitude, or thicken the membrane and watch the blood's oxygen saturation respond in real time.
SaO₂ 97%PaCO₂ 40 mmHgO₂ in 250 mL/minCO₂ out 200 mL/min
What to try
- Climb to 5 km. Why does the blood leave the lung less than fully saturated even though the air is still 21% oxygen?
- Breathe fast and deep. What happens to PaCO₂ — and could you actually blow off too much?
- Thicken the membrane to model emphysema. Which gas struggles first to cross — O₂ or CO₂?
- Switch to Exercise. The blood now races past the membrane — does it still have time to fully load oxygen?
- Combine high altitude with a thick membrane. How low can you push the O₂ saturation, and why do the two problems stack?