My investigation on the astronauts breathing of pure oxygen in spacesuits has led to these results. It is perfectly normal on takeoff and landing for astronauts to experience high metabolic heartrates do to excitement. There is a study done on this and it is comfirmed information. http://www.hq.nasa.gov/office/pao/History/x15conf/legacy2.html Could breathing pure oxygen at 3 psi, cause rapid heartrates up to 158 solely by doing physcial activity, in a gravity that is one sixth of ours? Is there any studies that have been done on this? Could the lack of these gases, play a contributing factor in spikes in heartrates over any period of time.