I have to agree with the Ferret on technique. The time honored way of dealing with health issues by relying only on chemicals needs to be modified by adding in better behavior. I have been learning to breath through the nose even when climbing and O2 is harder to come by. To my great surprise it works almost all the time unless I'm near the limit of aerobic capacity, then I breath through the mouth for a short time.

Coordinating the pedal with breathing also helps and this also helps high altitude mountaineers on Everest. Opera singers also pay close attention and work on breathing with the diaphram, both to increase oxygen uptake and voice control.