How to increase the efficiency of lungs

Humans (and mammals) have 2 lungs, one right and the another left. The right lung has 3 lobes and the left have 2 lobes because in the "third" there is the heart, so the right lung is bigger than the left.
I want to make a race with two hearts so I have to remove one lobe of the right lung to locate the heart and also I have to move a little the left heart.
If I remove a lobe this race would have a less pulmonary capacity and won't be able to run much. How can I overcome this problem?

My ideas are:

• Increase the size of the lungs: The problem is that I don't know if we have "free space" in our body to do that.
• Hollow bones: Some time ago I read that birds have hollow bones and they store air inside to breath later, then I found that is false but it is still an interesting idea. The problem with that is I would make bones less strong and I don't want that.
• Increase efficiency: I couldn't find any page with this information but 2 years ago I read that we inspire air with 21% O₂ and exhale with ~15% O₂, so we breathe the ~6% of O₂ in air. Maybe it's possible to increase this efficiency and exhale air with 10% O₂ or less to compensate for the lost lobe. The problem again is that I don't know if that it's possible or how to do that.
• EDIT ADDED:
  • Myoglobin: searching more about the ZioBite's answer I found the myoglobin, a substance similar to hemoglobin but instead of transport oxygen it's used to store oxygen in the muscles. This could explain how they can do physical effort but not how they live normally (because this store slowly the excess of oxygen not increase the oxygen input).

I had some ideas but I don't know if they are possible or how to do them.

posted over 7 years ago

Ender Look‭

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