Andrew Huberman· PhD
So, everyone has a sense of what a sigh is. We certainly, when we're emotional, in some ways we're stressed, we're particularly happy, [inhales] we'll take a little sigh. It turns out that we're sighing all the time. And when I would ask people who are not particularly knowledgeable that have read my papers or James Nestor's book or listened to your podcast, they're usually off by two orders of magnitude about how frequently we sigh on the low side. In other words, they say once an hour, 10 times a day. We sigh about every five minutes, and I would encourage anyone who finds that to be a unbelievable fact, is to lie down in a quiet room and just breathe normally, just relax, just let go, and just pay attention to your breathing and you'll find that every couple of minutes, you're [inhales] taking a deep breath and you can't stop it. It just happens. Now why? Well, we have to go back to the lung again. The lung has these 500,000,000 alveoli, and they're very tiny. They're 200 microns across. So, they're really, really tiny. And you can think of them as fluid filled. They're fluid lined. And the reason their fluid lined has to do with the esoterica of the mechanics of that. It makes it a little easier to stretch them with this fluid line, which is called surfactant. And surfactant is important during development, it is a determining factor in the, when premature infants are born. If they have not do not have lung surfactant it makes it much more challenging to take care of them than after they have lung surfactant, which is sometime, if I remember correctly, in the late second, early third trimester, which it appears. In any case it's fluid line. Now, think of a balloon that you would blow up, but now before you blow it up, fill the balloon with water, squeeze all the water out and now, when you squeeze all the water out you notice the sides of the balloon stick to each other. Why is that? Well, that's because water has what's called surface tension. And when you have two surfaces of water together, they actually tend to stick to each other. Now, when you try and blow that balloon up, you know that it, or you'll notice if you've ever done it before, that the balloon is a little harder to inflate than if we're dry on the inside. Why is that? Because you have to overcome that surface tension. Well, your alveoli have a tendency to collapse. There's 500,000,000 in them. They're not collapsing at a very high rate, but it's a slow rate that's not trivial. And when an alveolus collapses it no longer can receive oxygen or take carbon dioxide out. It's sort of taken out of the equation. Now, if you have 500,000,000 in them and you lose 10, no big deal, but if they keep collapsing, you can lose a significant part of the surface area of your lung.