Use NO2 Red tablets from GNC. They contain 8 hour time released L-Arginine, an amino acid that creates nitRIC oxide in your blood. This opens up all blood vessels including the capillaries in your lung's alveoli. Creates better O2 uptake and faster removal of lactic acid from your muscles. Yes it works just like Cialis (which mountain climbers use) but it's milder and a LOT less $$.
At altitudes over 7,000 ft. I find it helps noticeably.
Been using NO2 since 2000 and it always works. Also great for weight training. Improves strength more than you'd think. Not a cheap date but well worth the money.