Hyperbaric oxygen therapy is a natural medical treatment based on the combined action of oxygen and pressure. Hyperbaric oxygen therapy (HBOT) is defined as the inhalation of pure oxygen (100%), a subject placed in a pressure vessel made of steel or polymers, at pressures above atmospheric pressure (1.5 to 3 ATA). The therapeutic goal is the increase of the dissolved quantity of O2 in patient’s blood.

In general, hyperbaric treatments are provided over a period of about 90 minutes at a frequency of 1 to 5 treatments per week, depending on the indication.




The mechanisms of HBOT can be explained by the three physical laws described below.

The law of Boyle-Mariotte defines that at constant temperature; the volume (V) of a gas is inversely proportional to the pressure (P). In other words, the product P x V is a constant.

Pa x Va = Pb x Vb 

When the pressure increases from 1 ATA to 2 ATA, the volume of the gas decreases by 50%, while an equivalent increase from 4 ATA to 5 ATA, causes a change of only 5% of the initial volume. This is essential in the treatment of gas embolism because it reduces the volume of gas bubbles in the bloodstream of the patient.


Dalton’s law shows that the pressure of a gas mixture can be considered as the sum of the pressure of each gas component (PP partial pressures).

PPgaz1 + PPgaz2 + …+ PPgazn = Pmixed

To increase the oxygen partial pressure, we can either increase the concentration of oxygen (up to 100%) and/or the pressure of the mixture. The following table shows some cases.


Henry’s law states that at a given temperature, gas will dissolve in liquids in proportion to the partial pressure of each gas.

Cgaz = PPgaz / Hgaz     (H is the Henry’s constant of the related gas)

Therefore, the more the partial pressure of oxygen increases, the more the amount of oxygen dissolved in blood is important.

With these laws, we can calculate the amount of oxygen absorbed by the body during hyperbaric treatments.




Oxygen is essential to the functioning of the human body. Ambient air is composed of approximately 21% of oxygen. It is absorbed during the breathing cycle through the lungs, it passes into the blood and it is then distributed to the whole body. Oxygen is carried in the blood in two forms:

- In combination with hemoglobin in the form of oxyhemoglobin

- Dissolved in plasma

In ambient air and at atmospheric pressure (1 ATA), the quantity of oxygen transported as oxyhemoglobin is the largest, while the dissolved form is low, respectively 19.7 ml per 100 ml of blood and 0.285 ml per 100ml of blood. However, the physiological significance of dissolved oxygen is important because it is under this form that oxygen is spread to the tissues and provides cell supply.

HBOT essentially increases the amount of dissolved oxygen in plasma. This amount can be given by Henry’s Law. The following table shows the evolution in the amount of dissolved oxygen. At 3 ATA and 100% O2, this amount can reach 6 ml per 100 ml of blood. Under these conditions, the amount of dissolved oxygen is sufficient to cover the total needs of the body.


HBOT saturates the blood plasma with oxygen, making the cell osmosis process less energy consumption and allows the penetration of oxygen directly to the cells.




Effect of the increase of pressure

According to the Boyle’s law, the volume of gas decreases as the pressure increases. This effect is used in the treatment of gas embolism and decompression sickness.


Effect of the increase of the partial pressure of oxygen

Inhaling pure oxygen (100%) at high pressure (2.5 to 3 ATA) increases 15 to 20 times the amount of dissolved oxygen in blood and tissues. This oxygen can cover the total needs of the body and thus balance a malfunction of hemoglobin as in the case of carbon monoxide poisoning.


Vasoconstrictor effect

The vasoconstriction is the decrease in the caliber of a blood vessel. The elevation of the oxygen in arterial blood pressure causes a reaction of vasoconstriction of small vessels without significant reduction in the oxygen content delivered to the tissues. Hyperbaric oxygen therapy therefore helps to reduce edema (swelling) of certain tissues or organs.

HBOT allows to redistribute oxygen to the poorly oxygenated tissues caused by vasodilation of blood vessels (increase in caliber of a vessel).


Anti-infective effect

The increase of the oxygen pressure has a bactericidal effect on the anaerobic bacteria and promotes the action of white blood cells, which are essential for the immune defense of the body.


Anti-ischemic effect

Ischemia is the reduction of arterial blood supply to an organ, leading to hypoxia and stoppage of the potential function. By improving the elasticity and flexibility of red blood cells, HBOT allows them to better pass through affected small blood vessels. Along with the increase in the amount of dissolved oxygen in the blood, this phenomenon helps fight against ischemia through better tissue oxygenation.


Healing effect

HBOT leads to better healing of injured tissue. Indeed, it accelerates the synthesis of collagen by fibroblasts, fundamental process of wound healing, and stimulates the formation and growth of new blood vessels (neovascularization).