I don't know what an oxygen bar is, except on GTA: San Andreas, where your oxygen bar will slowly drop to 0 if you stay underwater too long and you will die.

Anyhow, it's not gasses that are building up in your lungs; it's tar. My theory is that this is pretty much the same as resin, and in the future maybe there will be a medical procedure called a resinectomy that could scrape all that resin out of your lungs so you could smoke it.