How come you can hold your breath for over a minute, but if you breathe a noble gas you lose consciousness in seconds?
In: Biology
Your body only uses some of the oxygen in air during most breaths. You inhale air at 21% oxygen and exhale about 16% oxygen. If you hold your breath, that percentage gradually keeps getting lower.
Also, when you exhale (normally, without forcing air out) about ⅓ the volume of a deep breath stays in your lungs. When you inhale normally, your lungs full to about ⅔ of that maximum volume.
So, say you suddenly enter a pure nitrogen gas environment:
– The first time you exhale, you’re left with lungs ⅓ full of 16% oxygen.
– Then you inhale (normally, not a deep breath), and fill your lungs to about ⅔-full. You’ve just diluted 16%-oxygen the air in your lungs with an equal amount of nitrogen (8% oxygen).
– You exhale again, and feel short of air so you take a deep breath this time, filling your lungs completely and diluting the 8%-oxygen air by three times. 2.7% oxygen now! And so on, getting worse.
When you hold your breath your body steadily works through the oxygen that is in your lungs and your bloodstream until the CO2 levels build up too much and force you to exhale, or the O2 levels drop too much and you pass out. Your blood has a fair amount of oxygen in it and a fair amount of CO2 capacity so it can last for a while
When you inhale a mix of gas that contains zero Oxygen, then the oxygen in your blood will leave your blood to join that gas until the partial pressure of the oxygen in the gas is the same as your blood. This means that not only is your body consuming the oxygen (which it can do for a minute without issue) but a large portion of the oxygen is being dumped uselessly into your lungs instead of delivered to your brain. Since your blood circulates every 30 seconds or so this means that you drain half the oxygen out of your blood in 15 seconds and that the blood making it to your brain at that point is now carrying basically zero oxygen causing you to promptly pass out.
Holding your breath is like idling your car engine and seeing how long a gallon of gas lasts, while breathing in a noble gas or inert gas mix is like hooking up a big pump to the gas tank to drain it super fast and wondering why your engine can’t idle as long.
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