In a hyperbaric chamber they are doing two things; they are increasing atmospheric pressure and they’re increasing the amount of inspired oxygen that you’re breathing.
Most of what they’re doing in a chamber is simulating the pressures you would feel if you were under a certain amount of sea water.
If you’re under -33 feet of sea water (-10 meters), you are at two atmospheres of pressure. You have one atmosphere at sea level, and then another (a hydrostatic atmosphere of pressure) at -33 feet of sea water, so two atmospheres total.
Now above you, if you’re -33 feet below the sea, you’re going to have a lot of water above you, and water’s very heavy and that’s really what we’re talking about; the pressure.
So the pressure itself is because water is extremely heavy. You don’t feel like the water’s heavy because you’re weightless in it, but if you carry a bucket of water you’re going to feel that heaviness.
So the hyperbaric chamber is simulating that atmospheric pressure increase, using a certain amount of sea water equivalent.
The second thing they do in a hyperbaric chamber is increase the amount of inspired oxygen that the person is breathing.
At sea level there is 21% oxygen in the air that we breathe and the rest of it is pretty much nitrogen. If you live in a city, you’re getting some carbon monoxide and some other terrible gasses that are coming from gasoline fumes, etc.
Now if you take out all of the nitrogen and you just add oxygen to it, which is what they do in the chamber, now you’re increasing the amount of inspired oxygen that the person is going to breathe.
Now we know that red blood cells carry oxygen. We have a vascular system that has veins and arteries, the arteries bring oxygenated blood from the heart to the rest of the body, and then they go into smaller and smaller blood vessels until the reach the veins and then the veins take blood that’s de-oxygenated and bring it back to the lungs to get it oxygenated again by way of the right side of our heart.
And when the de-oxygenated blood goes to the right side of our heart and then to our lungs, we take a breath in, the oxygen that’s in the air that we breathing (typically 21%) gets stuck on the red blood cells in the hemoglobin molecules, which there are four hemoglobin molecules per red blood cell.
Our bodies typically do a very good job using the oxygen in the air and creating enough oxygen carrying capacity to do everything that we need to do, as long as we basically have normal lungs.
What’s happening in a chamber, is they’re increasing the amount of inspired oxygen and so instead of 21%, the person’s getting 100% of oxygen, and they’re also pressurizing that oxygen at the same time.
Thing is, all those red blood cells are already pretty much already saturated with enough oxygen at sea level, so if you do a pulse oximeter on your finger, you’ll see a reading of 97%-99%. There’s not a whole lot more sites to really bind oxygen.
So the only ways you can really increase oxygen carrying capacity are by increasing the number of red blood cells in circulation, and that’s done through altitude training, through doping, things like auto-transfusions (so giving yourself more red blood cells), or giving yourself a drug like epogen, that increases the number of red blood cells in your circulation.
The other way to increase oxygen carrying capacity is what they’re doing in the chamber, and that’s by saturating more oxygen in the plasma, in the liquid of your blood.
When you saturate a lot of oxygen in the plasma, it’s actually liquid oxygen, that’s not actually bound to any red blood cells and this has a more significant ability to diffuse outside of the red blood vessel itself into the tissue around it.
So that’s significantly more potential to oxygenate your body.
So, what they’re doing in hyperbaric therapy is increasing atmospheric pressure, increasing the inspired oxygen to drive more oxygen into circulation to capacities that are impossible in any other way.
Source: Dr. Sherr, Scott, guest. “How Does Hyperbaric Oxygen Therapy Work?” Biohackers LAB, 8 August 2019. https://www.biohackerslab.com/ep95-dr-scott-sherr/