ElI5: Why is it easier to hold your breath on an inhale than an exhale?

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ElI5: Why is it easier to hold your breath on an inhale than an exhale?

In: Biology

Because your lungs are full of oxygen/air. That volume of air lasts longer than empty lungs.

Your blood is equivalent, but you have a lung full of reserves.

Your desire to breathe is driven by the carbon dioxide levels in your blood. When you have a full lungs there is some place for that carbon dioxide to go. That is it can be dissolved in all the air holding in your lungs. When you’re on the exhale there’s much less air in your lungs so much less volume to exchange the carbon dioxide into.

As the carbon dioxide levels rise the desire to breathe becomes stronger.

Note that this fact that it’s not a hunger for oxygen but a desire to get rid of carbon dioxide leads to some pretty bizarre conclusions .

For instance if you got into a giant inflatable balloon full of helium you will pass out and die before you realize you’re really in trouble. That’s because your body is able to get rid of the carbon dioxide but it’s not able to get any oxygen to replace it. So you won’t feel like you are not breathing until it’s far too late.

This is also why people who are hyperventilating are told to breathe into a paper bag. Hyperventilation is sort of a panic thing that happens when you lose the breathing reflex and you freak out. Breathing into the paper bag lets you recycle a few breaths of carbon dioxide enriched air. But the bag is smaller than your lungs so you’re not getting it 100%. This helps your body normalize the breathing reflex again.

When you think about it you’re simply adding the air in your lungs to the air and the space you’re in, and the purpose of breathing is just a stir that volume of air. When you close off your airway you are reducing the space from the space of the whole room or the whole world to simply the space in your lungs. And that space is far more limited.

Biology is fascinating.

Because when you inhale your lungs are full of air that your body can use. When you exhale, there is a lot less air and the oxygen level is lower because you’ve already used it.

I think a more interesting question is, why does slowly exhaling while holding your breath temporarily alleviate the feeling of needing to take another breath.