Oxygen is essential to the functioning of the human body. It is present in the ambient air at a concentration of about 21%. It is absorbed during the breathing cycle by the lungs, then it passes into the blood that carries it throughout the body. Oxygen is transported in the blood in two ways:
– Combined with hemoglobin in the form of oxyhemoglobin
– Dissolved in the plasma

In ambient air and at atmospheric pressure (1 ATA), the oxygen transported in the form of oxyhemoglobin is the most important, while the dissolved form is weak, respectively 19.7 ml per 100 ml of blood against 0.285 ml per 100 ml of blood. However, the physiological importance of the dissolved oxygen is considerable because it is in this form that it diffuses towards the tissues and ensures the cellular supply.

Hyperbaric oxygen therapy (HBOT) is essentially aimed at increasing the dissolved oxygen in the plasma, the quantity of which is governed by Henry’s law. The following table shows the evolution of the amount of dissolved oxygen. At 3 ATA and 100% O2, this amount can reach 6 ml per 100 ml of blood and life becomes possible without red blood cells. Under these conditions, the amount of dissolved oxygen is sufficient to cover the total needs of the body (Boerema in 1959).