This study is faulted, and from experience it is so by design. The study utilised 24% Oxygen at 1.3 ata chamber pressure by bleeding the  O2 into the chamber while running the compressor. The study should  have had the occupant breath "Oxygen" seperate from the air pressurising the chamber, and not just a 24% blend. The picture of the chamber that was part of the article was of a Performance Hyperbaric chamber which does not pressurise with oxygen but rather with air with O2 provided via a demand or non-breather mask; much much more effective. This study was probobly politically motivated; regardless, from a scientific perspective, it was, in my opinion, a farce!