Inhaled air is about 20% oxygen... exhaled air about 15%. So a small volume of dense oxygen might replace many breaths of much larger volume. (A speculative na

Inhaled air is about 20% oxygen... exhaled air about 15%. So a small volume of dense oxygen might replace many breaths of much larger volume. (A speculative nanotech dream for decades has been a manufactured red blood cell replacement, able to store and gradually release far more oxygen than naturally available - allowing cessation of breathing for hours if not days.)