This reminds me of the nose breathing athletic technique used to maintain blood CO2 levels. Strange that a waste product would be so integral to our health eh?
Discussion
nature tends to find a use for everything eventually. I'd guess this one dates back to the inception of cardiovascular circulation for larger animals that have a vast distance between the input and consumption of resources. By vast, I mean centimetres or more. Worms and slugs don't have a vascular system, and most small creatures like them rely entirely on motion and osmosis.