How are we able to hold our breath for so long? How do our vitals still receive oxygen?
In: Biology
Others have bought up good points, there is also the mammalian dive reflex to consider. Cold water on the face, like you’d experience diving into water, slow the heart rate and this slows the rate at which the body consumes oxygen.
I’m not sure what you mean by “so long”. While there are a handful of extreme examples, the average person can’t hold their breaths for more than a minute or two. It’s possible because we don’t use all of the oxygen from a breath right away. When you exhale, most of the oxygen you inhaled is still there. Your cells don’t extract all the oxygen from your blood in a single pass. Blood can take several passes around your body before it’s completely depleted of oxygen.
Your body does not run on such a tight metabolic framework that you are a single breath away from dying. That would be very disadvantageous.
You can hold your breath for however long you can hold it for, say 45 seconds, because your body has enough available oxygen both in your blood and in the last breath you took (and are holding) which is currently still “processing”, if you will.
This is also why you can hold your breath *longer* if you supplement with pure oxygen: because you’re temporarily raising your oxygen saturation level above its normal level and buying yourself a little time.
Think of oxygen like food, but on a much much tighter deadline. Holding your breath is like going without eating… except the timeline for consequences is minutes and not days/weeks.
You do not consume all of the oxygen in the air you take in during one breath. Inhaled air contains about 21% oxygen, exhaled contains about 16%. So you can see how you would have enough oxygen in a single breath for a while (minutes). The actual urge to take fresh air comes from wanting to get rid of the CO2, which decreases blood pH if accumulated. It’s all simple chemistry, gas exchange is governed by rules of diffusion (it’s a little more complex when you consider hemoglobin and how tightly you’re holding on to oxygen and CO2, but at the fundamental level it’s diffusion). So if your blood contains 5X O2 and 10X CO2 (random units), and the breath has 20X O2 and 0X CO2, these two will go down their concentration gradients raising blood O2 and lowering CO2. As you continue exposing your blood to this air in the lungs, you continue to exchange, but as the CO2 is on the rise in the lungs and O2 is dropping, and you keep producing more CO2 and using more O2, you reach a limit and need to take fresh air to re-establish steep enough gradients.
All these points about circulating oxygen are good, but another point to bring up is that oxygen isn’t the only way our bodies can produce energy. Some cells such as muscle cells can also perform lactic acid fermentation which is basically a way to make energy without oxygen. The problem is that this process does not produce enough energy to upkeep the body, certainly not the brain. Another problem is that lactic acid fermentation can change the pH or acidity of the environment, and that can cause its own set of issues too. This process is mostly associated with muscles because muscles use this process within seconds of muscle activity, so it’s going on much of the time you are active. But other cells are capable of this too.
Overall, this is only a small part of the picture of the answer to your question, but I didn’t see anyone else mention it, so I wanted to bring it up.
Also remember that if you stopped breathing right now, there is enough oxygen in your blood for you to have little to no brain damage for 10 minutes, *as long as your heart keeps pumping*. Sanjay Gupta wrote about this in the CPR chapter of his book Cheating Death. This is why CPR works even if you don’t do mouth-to-mouth. If you are taking in zero oxygen, as long as your heart is still pumping, your vitals are still getting the oxygen that is in your blood.
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