The Mechanism of Action (How does it work?)
There are two components to hyperbaric oxygen: increased ambient pressure and increased inspired oxygen concentration.
In essence, the amount of a gas (such as oxygen) that is dissolved in a liquid (such as blood) is directly proportional to the concentration of the gas at the surface of the liquid and the ambient pressure that the whole system is under. Thus, by having a patient breath 100% oxygen while in a pressurized chamber, hyperbaric oxygen therapy markedly increases the amount of oxygen in the patient's blood.
This increased oxygenation, or hyperoxia, has several beneficial effects. First, the high level of oxygen in the blood allows improved oxygen delivery to tissues that are not getting enough oxygen at baseline (i.e. hypoxic tissues). Second, having times of alternating hyperoxia and hypoxia (as occurs during a series of HBO treatments) promotes the growth of new blood vessels into the hypoxic tissues, a process known as neovascularization. Finally, hyperoxia enhances the body's ability to kill certain bacteria.
In addition to the above effects, HBO has various other effects such as shrinking air bubbles in the blood or tissue (as occurs in decompression illness-also known as the bends), and lessening the effects of inflammation and re-perfusion injury. However, most diseases that are helped by HBO are due to the three factors listed above.