How HBOT works: pressure, oxygen and Henry's law
The idea behind hyperbaric oxygen therapy comes down to a 200-year-old piece of chemistry called Henry's law.
Henry's law in one sentence
The amount of a gas that dissolves into a liquid goes up as the pressure of that gas goes up.
You see this every time you open a soda. The drink was bottled under pressure, so lots of carbon dioxide dissolved into it. When you release the pressure, the gas comes back out as bubbles.
How oxygen normally travels in your blood
Oxygen moves through your body in two ways:
- Bound to hemoglobin in your red blood cells. This carries the vast majority of it. In healthy people breathing normal air, hemoglobin is already about 95–100% saturated, so there is little room to add more this way.
- Dissolved in plasma, the liquid part of the blood. At normal pressure this is a very small amount.
What changes in the chamber
HBOT raises two things at once: the concentration of oxygen you breathe, and the surrounding pressure. Together they drive much more oxygen to dissolve into the plasma, many times the normal amount at typical medical pressures.
Because plasma reaches places red blood cells struggle to, such as tissue with damaged or narrowed blood vessels, this extra dissolved oxygen can help where oxygen supply is poor. That is the main reason HBOT is used for certain stubborn wounds and radiation injuries.
Pressure also shrinks bubbles
Boyle's law says that a gas bubble gets smaller as pressure rises. This is why HBOT is the standard treatment for decompression sickness and gas embolism: the pressure shrinks nitrogen or air bubbles in the body while the oxygen helps flush the nitrogen out. Read more in Decompression sickness: why divers need hyperbaric chambers.
Measuring pressure: ATA
Chamber pressure is measured in atmospheres absolute (ATA). Normal air pressure at sea level is 1.0 ATA. Medical treatments are typically between about 2.0 and 3.0 ATA. Many wellness chambers run lower, around 1.3 to 1.5 ATA. We compare the two in Mild vs. medical HBOT.
The short version
More pressure plus more oxygen means more oxygen dissolved in your blood. That simple physics is what every HBOT session is built on. What it can and can't do for a given condition is a separate question, and one for evidence and your doctor.