Reading this question about 1 mm tall people made me wonder: would a 1 mm tall person even be able to breathe? To someone of this size, the oxygen molecules around them would be much larger in proportion to their body, lungs and most importantly, cells. It seems like they might have difficulty with breathing enough oxygen in through their smaller lungs, and with their smaller cells bring able to process this oxygen.
Could a 1 mm tall person effectively process oxygen and continue to respirate, or would they asphixiate very quickly?
What would be the smallest a person could be and still successfully process enough oxygen to survive?
Note: I am aware that the 1 mm people in the question I referenced were actually robots. I'm specifically asking about a person that is 100% normal human, apart from being tiny.