Why do we not breathe back in the CO2 we just breathed out?

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We don’t breathe out with much force, and even if we did, we immediately inhale. So, how do we not just inhale what we just exhaled?

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Anonymous 0 Comments

You got the answer from others but i’ll ask a similar: so if you wait after exhale to inhale (slowly breath) you get more oxygen and thats why it makes you calmer?

Anonymous 0 Comments

The shortest answer is that gasses move around. You exhale, that dilutes in the atmosphere, then you breathe in nearly all fresh air.

There is some ‘dead’ air that leaves your lungs but doesn’t make it out your mouth or nose and is pulled in with your next breath. A baseline is around 150mL between nose, throat, and lungs. That may be around 30% of your total “breath”

Anonymous 0 Comments

We generally do, except when breathing hard during heavy exercise. This isn’t a big deal as long as there’s a net loss of some of the CO2 content in the blood.

CO2 in the blood is generally stored bicarbonate ions. There are enzymes in the internal surface of the lungs called “Carbonate Anhydrase” that rapidly convert bicarbonate ions into CO2 gas , carbonate ions, and hydroxide ions.

The production of hydroxide ions raises the pH of the blood. The hydroxide ions then react with hemoglobin in blood cells causing them to change shape in such a way that their oxygen binding affinity goes up by a factor of several tens of thousands of times. This causes them to absorb oxygen.

In other words, the process of absorbing and releasing O2 is *catalyzed* by a change in pH, caused by the blood absorbing or releasing CO2. The process in not 1-1 meaning that it’s nit the case that for every CO2 released, 1O2 is absorbed.

The concentration of CO2 in the air actually needs to be fairly high, around 1.5-2% before this process starts having problems. This is more than 10× it’s normal level in the air. Specifically, the reverse reaction starts taking place, CO2 gas is back-converted into bicarbonate ions, consuming OH- ions and reducing the blood pH. This starts reducing the efficiency of the hemoglobin to absorb O2. levels of 5% CO2 are immediately dangerous and will cause rapid incapacitation and eventual death after prolonged exposure of more than a few minutes.

Anonymous 0 Comments

Air always wants to be at the same pressure everywhere, if it can. So, if you have two pockets of air at different pressures, some air from the high pressure area will move to the low pressure area until the pressure is balanced between them.

However, the same happens with the individual constituent parts of air, and this is called partial pressure. In other words, if you have two pockets of air at the same overall pressure, but one of them is 90% oxygen and 10% CO2, and the other is 10% oxygen and 90% CO2, then the oxygen and CO2 molecules will quickly move around until both pockets have the same concentration of oxygen and CO2.

Therefore, when you breath out, you’re breathing out air that has less oxygen and more CO2 than the surrounding air. Your breath has partial pressures that are different than the surrounding air, so there will be pressure forces that cause the CO2 and oxygen levels to normalize quickly, and most of that normalization will likely be done before you’ve even started taking your next breath.

Also, just the force of pushing the air out of your mouth is enough to push that air far enough away that your next breath won’t take in very much of the same air that you just breathed out. Imagine someone taking a drag off a cigarette, breathing out the smoke, and then taking their next breath. How much of the smoke that they blew out do you think they’re inhaling on the next breath?

Anonymous 0 Comments

The space between your mouth and your lungs is referred to as dead air and it doesn’t get exhaled. We always reinhale it and it gets mixed up in our lungs with new air. And the air we just exhaled immediately starts mixing with the outside air so it’s a mix of both fresh air and not.

At the end of the day it’s not an issue for our breathing. Our lungs rely on differences in concentrations of gasses in the air and our blood to work. As long as the concentrations of oxygen in the air is higher than in our blood and the concentration of CO2 is lower in the air than our blood everything works. Breathing is just how we make sure the concentrations in our lungs are closer to the outside atmosphere than our blood. The lungs are very passive when it comes to which direction the gasses go in.

Take for example the ISS. It has to scrub CO2 out of the atmosphere or else astronauts can die, even if there is plenty of oxygen around. If CO2 concentrations get too high, then the CO2 in their blood can’t leave and will cause issues.

Anonymous 0 Comments

Just look at someone who vapes and just breathes out normally. The aerosol does disperses quite a lot and it is pretty obvious why you do not just breath in the same air.

The white stuff you see when someone vape is not vapor, it is an aerosol. Vapor is a gas and is invisible to us. What you see are small liquid droplets just like a cloud or fog, clouds can contain solid ice too. Droplets or solid suspended in air is called an aerosol

Anonymous 0 Comments

You do. Some of it at least. You are exhaling way less CO2 than you likely think.

When you inhale, you’re taking in 78% nitrogen, 21% oxygen, 0.04% CO2.

You exhale 78% nitrogen, 17% oxygen, 4% CO2, and the rest various gasses.

Anonymous 0 Comments

You do get some recycling in a stale room, but the air you exhale hasn’t been fully depleted of oxygen either.

Fresh air is 21% oxygen, and the air you exhale is 17%.

Gases do disperse very quickly (watch a smoker sometime) so you’re not just recycling the same quarter-lungful when you’re sitting down. Outside even a slight breeze will fully exchange the air in a second.

Anonymous 0 Comments

We do “reuse” a bit of air with each breath, but we don’t use up 100% of the oxygen with each breathe and we don’t breathe out 100% CO2 either. You can actually 100% rebreathe the same breathe several times and be perfectly ok, they use this concept for some SCUBA technologies to extend how much air you carry.

In case it’s your next question, it’s actually better for us to “keep” a bit of air with each breathe because our lungs don’t “re-open” very well, they work best when they’re already open a little bit. If you lung got 100% empty, you’re probably not be able to reopen them and you’d suffocate to death.

Anonymous 0 Comments

It mixes with the rest of the air so it’s not 100% what we breathed out, but there’s a decent component of it.

Regardless, though — we actually exhale _most of the oxygen we inhale_. You don’t consume all the oxygen you breathe in. Air you inhale is about 20% oxygen, and air you exhale is about 14% oxygen.

This is why you can give people mouth-to-mouth resuscitation, BTW (and yes I know that’s no longer recommended).