2 Year Member
You shouldn't really have to breathe deeper, just exhale more vigorously. Inhaling deeper doesn't make the oxygen content any better, it just gives you a little more volume. It's the exhalation that we struggle with at the upper altitude, not so much the inhaling. The drained feeling you get in the higher altitudes is a build up of lactic acid because your inhalation is less efficient. When people strap on oxygen they decrease the gradient, which improves carbon dioxide removal from the lungs.