Belived (139, 142). This higher barometric pressure increased the estimated inspired PO2 and made a big difference in the predicted VO2 max. Figure 24.5 shows that the VO2 max predicted from the 1960-1961 expedition was near the basal metabolic rated, whereas the value predicted from the 1981 expedition was closer to 15 ml kg-1 min-1 (139, 142). This VO2 max value was confirmed in the Operation Everest II project in which subjects did a simulated ascent of Mount Everwhich subjects did a simulated ascent of Mount Everest over a 40-day period in a decompression chamber (29,125). This VO2 max value of 15 ml kg-1 min-1 helps to explain how the climbers were able to reach the summit without the aid of supplemental oxygen. However, it was not eh only reason.