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There's a point at which you can't voluntarily hold your breath anymore.
有时你不能再主动屏气了。
Sometimes that's 30 seconds into a breath hold, sometimes a minute, sometimes multiple minutes if the conditions are just right.
有时是屏住呼吸后的30秒，有时是一分钟，有时是几分钟，如果条件合适的话。
Everyone's breakpoints are different, and individually, multiple factors influence our time on the stopwatch.
每个人的极限都是不同的，而且有多种因素影响着我们的屏息时间。
But how does your body know that you're at your breaking point?
但是你的身体是如何知道自己已经到临界点了？
When do you know you've reached your absolute limit you know, before death?
你什么时候知道你已经达到了死亡前的绝对极限？
As it turns out, it has to do with what's in our blood.
事实证明，这和我们血液里的东西有关。
In this video, we'll go over the physiology that monitors your blood chemistry and keeps you breathing right.
在这段视频中，我们将回顾监控你血液化学和保持你呼吸正常的生理学。
Quick disclaimer, I'm going to talk about intentional breath holding in this video, not choking or which are emergencies.
一个简单的声明：我将在这个视频中谈论故意屏气，而不是窒息或气道阻塞，这两种都是紧急情况。
Also, some young infants and toddlers experience involuntary breath holding spells, but this video is for curiosity and education, not medical advice.
此外，一些婴儿和学步幼儿会出现不自觉的屏气，但这段视频是出于好奇和教育，而不是医疗建议。
So please, please use common sense.
所以请使用常识。
If you think something is wrong, get professional medical help.
如果你认为有什么不对劲的话，就请寻求专业的医疗帮助。
Okay, now we can get into the fun stuff.
好了，现在我们可以开始聊一些有趣的事情了。
The whole point of breathing is so that our tissues can consume oxygen and glucose and turn them into energy, leaving water and carbon dioxide as waste products.
呼吸的全部意义在于，我们的组织可以消耗氧气和葡萄糖，并将它们转化为能量，留下水和二氧化碳作为废物。
This process called cellular respiration is essential to anything that breathes oxygen.
这个被称为细胞呼吸的过程对任何呼吸氧气的生命体都是必不可少的。
And if our tissues don't get enough oxygen, or experience hypoxia, they can start to die off or see other problems.
如果我们的组织得不到足够的氧气，或者缺氧，它们就会开始死亡或者出现其他问题。
There are a bunch of reasons that a tissue might not get enough oxygen - like an iron deficiency might cause anemia, which means that less oxygen will be able to ride on each red blood cell and oxygenate your tissues.
一个组织可能得不到足够的氧气有很多原因，比如缺铁可能会导致贫血，这意味着更少的氧气能够附着在每个红细胞上，给你的组织充氧。
Hypoxia can also happen if there's not enough blood flow to a tissue, like when an artery is too narrow and doesn't deliver as much blood to its target tissue.
如果没有足够的血液流向组织，比如动脉太窄，不能向目标组织输送足够的血液，也会发生缺氧。
Then there's high altitude where oxygen isn't as easily available, but we'll come back to that later.
氧气在高海拔地区是不容易获得的，但我们稍后再讨论这件事。
Now, in a breath holding situation, it's pretty easy to see why you'd become hypoxic.
现在，在屏气的情况下，很容易理解为什么你会变得缺氧。
You're not breathing so you're not taking in any of that sweet sweet oxygen.
你不能呼吸，所以你无法吸入任何氧气。
But we have to keep another gas in mind during breath holding - carbon dioxide.
但我们在屏息时必须要想到另一种气体——二氧化碳。
High CO2 levels in our blood, or hypercapnia, can cause symptoms like headaches and dizziness, but also more severe symptoms like paranoia, irregular heartbeats, and seizures.
我们血液中的高二氧化碳水平，或高碳酸血症，会引起头痛和头晕等症状，但也会引起更严重的症状，如偏执、心律失常和癫痫。
Hypercapnia can happen without breath holding too, like if you're in a submarine or just a stuffy room with the windows closed.
高碳酸血症也会在没有屏气的情况下发生，比如你在潜水艇里或者在一间窗户关着的闷热房间里。
Since neither hypoxia or hypercapnia are ideal, our bodies are constantly measuring and reacting to oxygen and carbon dioxide in the blood.
由于缺氧和高碳酸血症都不是好的现象，我们的身体不断地测量血液中的氧气和二氧化碳并对其作出反应。
