The mechanisms of action of HBOT can be explained by the following three physical laws.
Boyle-Mariotte’s law 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
When the pressure increases from 1 ATA to 2 ATA, the volume of the gas decreases by 50%, whereas the same increase from 4 ATA to 5 ATA causes a variation of only 5% of the initial volume. This phenomenon is essential in the treatment of gaseous embolisms because it reduces the volume of gas bubbles present in the patient’s blood system.
Henry’s law states that at a given temperature, gases dissolve in liquids in proportion to the partial pressure of each of these gases.
(H is Henry’s constant of the gas concerned)
As a result, the higher the oxygen partial pressure, the greater the amount of oxygen dissolved in the blood.
Thanks to these laws, we can calculate the amount of oxygen absorbed by the body during a hyperbaric treatment.
Dalton’s law shows that the pressure of a gas mixture can be considered as the sum of the pressures of each constituent gas (partial pressures PP).
To increase the partial pressure of oxygen, it is therefore sufficient to increase its concentration (up to 100%) and / or the pressure of the mixture. The following table presents some situations.
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).
Hyperbaric oxygen therapy thus helps to reduce edema (swelling) of certain tissues or organs. HBOT allows a redistribution of oxygen in favor of poorly oxygenated tissues induced by vasodilatation of the vessels.The increase in oxygen pressure has a bactericidal effect on anaerobic bacteria and promotes the action of white blood cells, essential elements of the immune defense of the body.
Ischemia is the reduction of arterial blood supply to an organ, leading to hypoxia and then to the potential arrest of its function. By improving the elasticity and flexibility of red blood cells, HBOT allows them to better sneak into injured small vessels. Combined with the increase in the amount of oxygen dissolved in the blood, this phenomenon makes it possible to fight against ischemia thanks to a better oxygenation of tissues.
HBOT leads to better healing of injured tissues. In fact, it accelerates the synthesis of collagen by fibroblasts, a fundamental process of healing, and stimulates the formation and growth of new blood vessels (neovascularization).
Inhaling pure oxygen (100%) at high pressures (2.5 to 3 ATA) increases the amount of oxygen dissolved in the blood and tissues by 15 to 20 times. This quantity of oxygen makes it possible to cover the total needs of the body and thus to overcome a dysfunction of the hemoglobin as in the cases of poisoning with carbon monoxide
Hyperbaric oxygen therapy is a proven treatment. The Undersea & Hyperbaric Medical Society (UHMS) recognizes the effectiveness of this therapy for treating fourtheen disease states listed below.
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