NASA Prebreathe Study

"Subjects will be exposed to simulated altitude (30,000 ft, 4.3 psia) in a hypobaric chamber. This is the same ambient pressure to which astronauts are exposed during EVA (space walks)."

Oxygen pre-breathing prior to altitude or simulated high altitude exposure is routinely used by the Air Force, NASA and organizations such as Duke Medical Center to prevent and treat decompression sickness as well as for treatment of patients. Oxygen used for this study is medical grade.