Altitude exposure increases red blood cell mass; what is the primary consequence for oxygen transport?

• A. Decreases red blood cell mass.
• B. Increases red blood cell mass, improving oxygen transport at altitude.
• C. Increases CO2 transport.
• D. Decreases oxygen-carrying capacity.

Answer: (B)

Altitude lowers the amount of available oxygen, so the body increases red blood cell production via erythropoietin. More red cells mean more hemoglobin, boosting the blood’s oxygen-carrying capacity. Even with a lower ambient PO2, arterial blood can hold more oxygen because of the higher hemoglobin concentration, improving oxygen transport to tissues. This adaptation is beneficial, though it can raise blood viscosity if the rise in red cells is large. The idea that red cell mass would decrease, that carbon dioxide transport would be the primary change, or that oxygen-carrying capacity would drop does not fit how the body adapts to altitude.