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Author Topic: What is the lowest surviveable oxygen level in the atmosphere?  (Read 44320 times)

Offline thedoc

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Allen Woodruff asked the Naked Scientists:
Since the atmosphere is only 20% oxygen, each time we breathe we only use a maximum of 20% of each usable breath. Do we use 100% of the available oxygen with each breath or is a percentage expelled? What is the lowest percentage oxygen in an atmosphere that which a person can function normally? Are there other naturally occurring gases in our atmosphere that our body also utilizes?

What do you think?
« Last Edit: 14/07/2012 16:30:01 by _system »


Offline C-Jackson

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A lot of questions here, let's see if we can answer them in order:
First, we do not use all of the oxygen we inhale with each breath.  It depends a lot on how hard the body is working, but you usually exhale about 16% oxygen and 4-5%CO2.
Lowest percent of oxygen for a human to function normally? That depends a lot on the person's conditioning, and what you mean by normally.  I am a sea-level conditioned human, if you take me to the top of a 14K foot mountain, even walking will make me short of breath.  At this altitude, the partial pressure of oxygen is about 12%, whereas at sea level it is 21%.  There are people conditioned to high altitudes who could run a race at that partial pressure.  These people have higher hemoglobin concentrations in their blood, and so, can extract oxygen more efficiently from the air.  Here's a cool site that gives oxygen partial pressures for elevations: newbielink: [nonactive]
To my knowledge, there are no other gasses in the atmosphere that we utilize in metabolism, but it is dangerous to breathe pure oxygen for long periods of time.
As far as what is the lowest survivable oxygen concentration: you will pass out at a low concentration (probably around 10% if you are not acclimated) but this does not cause death.  As oxygen concentrations decrease, to around 5% the body starts to shift blood flow away from less vital organs to the brain.  Long term exposure to these low concentrations can cause organ failure and brain damage, but you could survive.  Unfortunately, as the heart works harder to pump more blood to the brain, it consumes more oxygen itself.  Death usually occurs by cardiac arrest as this stress continues.

Offline evan_au

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"Mouth-to-mouth resuscitation" works by taking the left-over oxygen from your exhaled breath, and breathing this into the lungs of a person who cannot breathe for themselves.

Provided their heart is working (or is being externally pumped), there is enough oxygen in this exhaled air to keep them alive until an ambulance arrives with more advanced equipment like an oxygen mask.

Offline Lmnre

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Lincoln Hall (barely) survived overnight at an unprecedented 8,600 meters (28,200 ft) on Mount Everest breathing 34% of the oxygen available at sea level (that is, less than 7% compared to the regular 20%).

Offline CliffordK

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High altitude training will produce a slight shift in Red Blood Cell Count (RBC), as one adapts to the low atmospheric pressure (the oxygen percentage is about the same).

High altitude populations have also adapted to the environment to some extent.

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