A hyperbaric chamber works by surrounding your body with pure oxygen at pressures higher than normal atmospheric levels, which forces significantly more oxygen into your blood and tissues than you could ever absorb by breathing normally. Most clinical chambers pressurize to about 2.0 to 2.2 times normal atmospheric pressure, and a typical session lasts a little over two hours. The result is a cascade of biological effects: shrunken gas bubbles, supercharged oxygen delivery, new blood vessel growth, and the mobilization of your body’s own repair cells.
The Physics Inside the Chamber
Two basic gas laws explain almost everything happening inside a hyperbaric chamber. The first is the principle that gas volume shrinks when pressure increases. Double the pressure and a gas bubble is compressed to half its original size. This is why hyperbaric therapy is the primary treatment for decompression sickness in divers: nitrogen bubbles trapped in blood and tissue physically shrink as soon as the chamber pressurizes.
The second principle governs how gases dissolve into liquids. At higher pressures, more gas dissolves into a liquid, the same way carbonation stays dissolved in a sealed bottle of soda but fizzes out when you pop the cap. Inside the chamber, oxygen is pushed into your blood plasma at levels far beyond what your red blood cells alone can carry. Under normal conditions, almost all the oxygen in your blood rides on hemoglobin molecules inside red blood cells. Under hyperbaric pressure, plasma itself becomes saturated with dissolved oxygen, creating a secondary delivery route that can reach tissues where blood flow is compromised or blocked.
These two effects work in sequence during treatment. Pressure first compresses any trapped gas bubbles, then dissolves the gas completely into the surrounding fluid so it can be safely cleared by the body.
How Extra Oxygen Changes Your Biology
Flooding tissues with oxygen does more than just compensate for poor circulation. It triggers several repair mechanisms that persist well after you leave the chamber.
One of the most striking effects involves stem cells. A single two-hour session at 2.0 times atmospheric pressure doubles the number of circulating stem cells (specifically, a type involved in blood vessel repair) in your bloodstream. Over the course of 20 treatments, that number increases eightfold, without a significant change in your overall white blood cell count. These cells home in on damaged tissue and contribute to rebuilding injured blood vessels.
Hyperbaric oxygen also stimulates the production of growth factors that drive angiogenesis, the process of sprouting new blood vessels from existing ones. Tissues starved of oxygen by chronic wounds, radiation damage, or vascular disease gradually develop new capillary networks that improve blood supply long term. This growth factor response has been documented within 24 to 48 hours of treatment in laboratory studies.
High-pressure oxygen also enhances the ability of white blood cells to kill bacteria, which is part of why the therapy is used for serious infections in bone and soft tissue. Oxygen-starved environments are where many dangerous bacteria thrive, and restoring oxygen levels shifts the advantage back to your immune system.
Types of Chambers
Clinical hyperbaric chambers come in two main designs. Monoplace chambers are clear acrylic tubes sized for one person. The entire tube fills with 100% oxygen, so you simply breathe normally without wearing a mask or hood. These hard-shell monoplace units can reach pressures up to 3.0 atmospheres and are FDA-cleared to treat 14 different medical conditions.
Multiplace chambers are room-sized and hold several patients at once. Because the whole room is pressurized with air rather than pure oxygen, each patient wears a hood or mask that delivers 100% oxygen individually. These larger chambers also allow a medical attendant to be inside with patients during treatment, which can matter for critically ill or anxious individuals.
A third category, soft or “mild” portable chambers, exists on the consumer market. These inflatable units max out at only 1.3 atmospheres and are FDA-authorized solely for acute mountain sickness. They cannot replicate the pressures or oxygen concentrations used in clinical treatment.
What a Session Feels Like
A standard treatment session lasts a little over two hours total. At Michigan Medicine, for example, patients receive 90 minutes of oxygen breathing with two 10-minute air breaks built in, plus additional time for gradually increasing and decreasing pressure at the start and end.
The most noticeable sensation is pressure in your ears during the initial compression phase, similar to what you feel during airplane descent. Yawning and swallowing help equalize the pressure. Some facilities call their sessions “dives” because the pressurization process mimics descending underwater. Once the chamber reaches treatment pressure, most people settle in comfortably. Many facilities allow you to watch television or rest during the session.
Decompression at the end is gradual and controlled. The entire process is designed to avoid the very pressure-related injuries the therapy can treat, so the pressure changes happen slowly enough for your body to adjust.
What Hyperbaric Therapy Treats
The best-established use is decompression sickness and arterial gas embolism, conditions where gas bubbles are physically trapped in the bloodstream. For these emergencies, hyperbaric oxygen is the definitive treatment, not an optional add-on.
For chronic wounds, the therapy works as an adjunct to standard wound care rather than a replacement. In diabetic foot ulcers complicated by poor arterial blood flow, a meta-analysis of 729 patients across 11 studies found that adding hyperbaric oxygen cut the rate of major amputations from 26% to about 11%. That translates to preventing one major amputation for roughly every seven patients treated. The therapy did not, however, significantly improve complete wound closure rates on its own, highlighting that it works best as part of a broader treatment plan.
Other recognized uses include carbon monoxide poisoning (where oxygen displaces the carbon monoxide bound to hemoglobin), radiation injury to bone and soft tissue, certain severe bone infections, compromised skin grafts, and crush injuries. The common thread across all these conditions is tissue that is oxygen-starved, infected in a low-oxygen environment, or contains trapped gas.
Why Pressure Matters More Than Just Oxygen
You might wonder why you can’t get the same benefit from breathing pure oxygen at normal pressure through a mask. The answer comes back to gas solubility. At sea-level pressure, breathing 100% oxygen increases your blood oxygen levels somewhat, but plasma can only dissolve a limited amount. Raising the pressure to 2.0 or 2.2 atmospheres dramatically increases the amount of oxygen that physically dissolves into plasma, pushing it into tissues that compromised blood vessels can’t reach through normal hemoglobin delivery. The pressure is doing the heavy lifting, not just the oxygen concentration.
This is also why the number of sessions matters. A single treatment produces measurable changes in stem cell counts and oxygen levels, but the tissue remodeling effects, like new blood vessel growth, build over a course of 20 to 40 sessions depending on the condition. Most treatment plans are designed around daily sessions five days a week for several weeks.