Kathleen, oxygen might be an indirect element in the mystery because I think Zina or Lyuda extracted a promise from the guys not to smoke. Now, considering the guys had sedentary occupations and a tobacco habit, they may have believed they had more endurance that was the actual case. After all, for the lion's share of the adventure they were riding something. Once they began the ascent of the Auspya and faced the conditions, things slowed down, people,were punished for slowing progress and the whole expedition looked like anything but a race to Ortoten. That, plus altitude are factors we can not ignore. I would also add that swearing off smokes is going to make for some grumpy guys.