On the earth’s surface, we are subjected to the pressure exerted by the atmosphere (atmospheric or barometric pressure). And we breathe air, a mixture of nitrogen (79%) and oxygen (21%).
Changes in the pressure around us; it decreases if we climb a mountain, and increases if we go down for example to a mine or into the sea; also if we increase the pressure in a hyperbaric chamber. This has effects on the body, especially on the organs that contain air (lungs, ears, sinuses, digestive system).
According to the laws of physics, gases in contact with a liquid dissolve in proportion to that pressure so that the amount of dissolved gas increases as the pressure increases and decreases as the pressure decreases.
Treatment with hyperbaric oxygen therapy (HBO) consists of breathing 100% oxygen at higher pressure than atmospheric pressure; this achieves the oxygen to dissolve in the plasma and reach the cells in a much greater quantity, producing therapeutic effects.