Question:
I'm wondering about for how long the brain can go w/o oxygen, before braindamage occurs? (And also, how the damage occurs..)

For example, if I breathe out as much air as possible, in less than 10 seconds I will feel the need to inhale. Does this mean that if I could go on longer w/o inhaling, something ..bad would happend?

I've read reports of people inhaling pure N2O (as opposed to the dental 30%/ 70% mix, or whatever amount it is and holding it in for minutes, would this mean that some sort of damage occurs?

Answer: I believe, NO2 (not N2O), i.e. nitrous oxide. I believe there has been some evidence published that suggestts long-term abuse of this gas may cause brain damage. I believe tthe interpretation has been that this is due to hypoxia, but it occurs to me that the (as yet little studied) possible consequence of increased brain levels of NO (nitric oxide) might also play a role...

Under 'normal' situations, brain cell begin to die in large numbers around four minutes. By six minutes brain damage is "likely" and over ten minutes, there WILL be irriversiable brain damage. the first priority in CPR being to introduce O2 to the lungs. At one time it was thought that a human could not survive with out oxygen for more than five to seven minutes. But there is one major area of exception involving cold water imersion. there are many recorded cases of subjects (usually children) spending over 15 minutes submerged in water under 41 degrees and surviving. It is thought that the cold slows the body to a core survival state that allows a shutdown of all body systems, allowing the minimal blood flow to supply the brain. this cooling allows oxygen to remain in the cells longer. However, it seems that one in three of these survivors suffers neurological damage.