How Does Hyperbaric Oxygen Therapy Work?

How your blood normally carries oxygen

Most of the oxygen in your blood rides on hemoglobin, the protein inside red blood cells. At sea level, breathing ordinary air, the hemoglobin in your arteries is already close to fully loaded. That means breathing more oxygen at normal pressure cannot add much through hemoglobin, because there is little room left.

A much smaller amount of oxygen is dissolved directly in the plasma, the liquid part of your blood. Under normal conditions, that dissolved share is small, about 3 milliliters of oxygen per liter of plasma. The trouble comes when tissue is poorly supplied. If blood vessels are narrowed, damaged or scarred, red blood cells may not reach every cell that needs oxygen, and healing can stall.

Henry's law: pressure dissolves more gas

HBOT works on the dissolved share. Henry's law, a basic rule of gas physics, says the amount of a gas that dissolves in a liquid is directly proportional to the pressure of that gas above the liquid. You can see the same principle in a sealed soda bottle: under pressure, carbon dioxide stays dissolved in the drink.

Raise the pressure, and raise the oxygen concentration you breathe, and far more oxygen dissolves into your plasma. According to the StatPearls reference on hyperbaric physics, dissolved oxygen rises from about 3 mL per liter at 1 ATA to about 60 mL per liter when breathing oxygen at 3 ATA. That is roughly a twentyfold increase, and about the amount tissues typically use at rest.

Because plasma flows where red blood cells may struggle to go, and because higher oxygen levels in the blood push oxygen farther out into surrounding tissue, this extra dissolved oxygen can reach areas that normal circulation leaves short. The effect lasts while you are under pressure. Oxygen levels in your tissues return toward normal after the session ends.

Boyle's law: pressure changes gas volume

A second gas law explains some of what you feel in the chamber. Boyle's law says the volume of a gas shrinks as pressure rises and expands as pressure falls. That is why your ears feel full as the chamber pressurizes, much like descending in an airplane, and why you learn to clear them. The same law is the reason pressure is used in hospital treatment of gas bubbles in the body, such as decompression sickness.

The physics explains how oxygen gets in. The biology explains why that matters. Researchers have described several effects of repeated HBOT in laboratory and clinical studies. These are mechanisms, not promises: how much any one person benefits depends on their condition, and a physician decides whether HBOT is appropriate.

Oxygen reaches starved tissue

Wounds with poor blood supply are often low in oxygen. The cells that rebuild tissue, such as fibroblasts, need oxygen to make collagen, the protein that gives new tissue its strength. During each session, HBOT temporarily raises oxygen levels in and around that tissue. Reviews of HBOT mechanisms describe improved collagen production and tissue remodeling as part of how it may support healing in selected problem wounds.

New blood vessel growth (angiogenesis)

One of the most studied findings is angiogenesis, the growth of new small blood vessels. In a widely cited 2011 review, Dr. Stephen Thom describes how high oxygen levels trigger chemical signals in cells that increase growth factors such as VEGF (vascular endothelial growth factor), which is involved in forming new vessels. Research has reported increased VEGF in wounds treated with HBOT. Over a course, new vessels may help damaged tissue keep a better oxygen supply after treatment ends. This is one reason HBOT is used as an adjunct for delayed radiation injury, where radiation has damaged small blood vessels.

Less swelling

High oxygen levels cause small blood vessels to narrow slightly, a response called vasoconstriction. That can reduce the fluid that leaks out of vessels into injured tissue, which is what swelling is. Normally, narrower vessels would mean less oxygen delivered. Under hyperbaric conditions, though, the large amount of oxygen dissolved in plasma can more than make up the difference, so tissue may get less swelling without losing oxygen.

Help fighting infection

White blood cells use oxygen to kill bacteria, and that process works poorly in oxygen-starved tissue. Raising tissue oxygen may support this normal defense. High oxygen levels are also hostile to certain bacteria that thrive without oxygen. For these reasons, HBOT is used alongside antibiotics and surgery, never instead of them, for some serious infections such as chronic refractory osteomyelitis.

Findings at the cell level

Thom's review also summarizes studies reporting that HBOT raised the number of circulating progenitor cells, which are cells involved in tissue repair, in healthy volunteers and some patient groups. These are research observations about physiology. They have not been shown to be a treatment benefit on their own, and we do not present them as one.

Because the effects of HBOT depend on pressure and oxygen, the kind of chamber matters. There are three broad types:

• Monoplace chambers. Hard-shell chambers built for one person. Under the NFPA 99 safety code they are Class B chambers, and they are typically pressurized with oxygen, so you breathe it directly without a mask.
• Multiplace chambers. Larger hard-shell rooms that hold two or more people, often with an attendant inside. They are Class A chambers under NFPA 99. The room is pressurized with air, and each patient breathes oxygen through a mask or hood. These are mostly found in hospitals.
• Soft-sided "mild" chambers. Fabric chambers that typically reach about 1.3 ATA, usually on air. The UHMS says they do not meet the definition of HBOT, and they are FDA-cleared only for acute mountain sickness.

Medical hard-shell chambers are pressure vessels, built to the ASME PVHO-1 standard, and installed and operated under NFPA 99. At Generations Wellness we use hard-shell monoplace chambers, where you breathe medical-grade oxygen at a pressure your physician prescribes. For the full comparison, read hard-shell vs. soft-shell chambers.

The mechanisms above explain why HBOT is an FDA-cleared treatment for a specific list of conditions. That list includes selected diabetic wounds of the lower legs, delayed radiation injury, compromised skin grafts and flaps, chronic refractory osteomyelitis and sudden sensorineural hearing loss. It also includes emergencies such as carbon monoxide poisoning, decompression sickness and gas embolism, which are treated at hospital-based chambers. See the full list of conditions HBOT is cleared for.

A plausible mechanism is not the same as proof. The FDA has warned that HBOT has not been cleared for many uses promoted online. For an honest look at those, read what the evidence says about other uses.