|The Scream (Edvard Munch)|
A human being can survive after more than fifteen days without eating, or more than three days without drinking. We can't, however, survive without breathing for more than a few seconds. Breathing is the process that provides oxygen to our body. Our cells need oxygen at every moment to obtain energy by respiration (into organelles called mitochondrions) and carry out their vital functions and inner or outer cellular activities.
At rest, a human being breathes about twelve times per minute, exchanging approximately six litres of air. If we are doing some physical exercise, the requirements of oxygen rise, so we will breathe with more frequency and depth. In extreme conditions we could increase the exchange to more than forty litres per minute.
We need to breathe constantly. So we can stand under water, without oxygen supply, for only little time. People who like diving must improve their capacity to hold their breath (what we call apnea). The longer you could hold your breath, the better diver you would be. Many divers use a trick called hyperventilation to increase their capacity to stand in apnea: after hyperventilation, you can really hold your breath for longer.
What is hyperventilation? Simply, hyperventilation consists of doing several very deep inhalations and exhalations. For one minute or so, we exchange as much air as possible. After that, our ability to hold our breath will be at least dobule.
How does this process work? It's important, because many people practice it when they dive, but they don't know that it could be a bit dangerous if it's done without control.
Most people think that the process works raising the amount of oxygen that we are able to take, although that is nonsense. If we measure the saturation of our arterial blood, we will find out that it must be between 99% and 100% all the time. The oxygen is transported in our blood linked to haemoglobin, into the erythrocytes (red cells of our body), and all the haemoglobin is full of oxygen for the whole time in our arteries (our veins transport deoxygenated blood from our tissues, so its saturation is quite lower).
So, if saturation is always close to 100%, it can't be higher in any way. In fact, when our cells need more oxygen, our heart pumps our blood more quickly, so more blood arrives at the lungs and the tissues, and more exchanges and respiration processes are possible.
Let's return, then, to the question, because, if hyperventilation doesn't increase our capacity to take oxygen, how does it work? The answer is not related to oxygen, but to the other gas exchanged during respiration: carbon dioxide.
Carbon dioxide is a waste product of cell metabolism. To obtain energy, cells combust glucose using oxygen and producing energy and carbon dioxide. This molecule must be eliminated, so our cells pass it to the blood. Blood carries carbon dioxide to the lungs, where it is released to the exterior.
Carbon dioxide is transported in our blood mainly transformed to bicarbonate. Production of bicarbonate, besides, reduce the pH of our blood, due to the acid nature of this substance. And bicarbonate and pH are the most important signals that our body detects when the amount of gases starts to be a problem.
What it means is that when we hold our breath, the supply of oxygen decreases slowly, but the amounts of bicarbonate of our blood rises quickly, and the pH decreases. Our body has many chemical receptors that alert our brain when the bicarbonate levels are high or the pH is low. In fact, these are the most important signals that make our brain urge us to breathe, because they can be detected before the levels of oxygen decrease to dramatical levels.
When we hyperventilate we don't increase the amount of oxygen of our blood, but we reduce the amount of bicarbonate and increase pH. So, after hyperventilating we will be able to hold our breath for longer, because the levels of oxygen are no higher, but the levels of carbon dioxide are much lower. And it will take long time until this level is high enough to make the receptors send the warming alert to the brain.
Diving (author: matthew lee)
Hyperventilation can be dangerous, because if it is used without control the levels of carbon dioxide could descend to extremely low levels. Sometimes, the amount of carbon dioxide is so low that the diver doesn't feel the necessity to breathe for too long, and then the levels of oxygen fall dramatically, so dramatically that it's brain lacks oxygen, but the warning signs have not been sent. And the diver, in that situation, could faint. On land that's not a problem, because when a human loses its conscientiousness starts breathing automatically. However, if this occurred under the water you would drown in few seconds.
For this reason, hyperventilation is a good way to improve our capacity to hold our breathe, but is not free from dangers, so it must be done carefully and under the control of another person.