how does that work? wrote:
How do they extract more oxygen from the same volume of air?
There are, in fact, legitimate questions about why and to what extent EPO improves performance. It's not as obvious as some would have it. Different factors limit performance, and their interaction isn't entirely clear.
The specific questions you're asking here about thermodynamics and respiration, on the other hand, are inane. You extract more oxygen from the same volume of air because your blood has more capacity. Everyone has plenty of oxygen in their lungs when they exhale. That's why CPR works. Incidentally, blood is almost always fully oxygenated when leaving the lungs, regardless of RBC count, so there's no question that higher RBC count increases the amount of oxygen the blood can move.
To be sure, having more or less oxygen in the air ALSO affects the effectiveness of diffusion into the blood (e.g., running at altitude or using supplemental oxygen). But it's not an either/or situation. In fact, the entire premise of your questioning seems to make the same error that the EPO skeptics accuse others of making: Assuming that only one thing can be a limiting factor at a time. RBC can't be a limiting factor, you claim, because other things are. That's nonsense.