The benefits of HBOT are based on the therapeutic principles involved in its use. The increased overall pressure used in the HBOT has been used in the treatment of decompression sickness and air embolism. Decompression sickness (DCS), also known as diver’s disease, the bends, or caisson disease is a condition caused by dissolved gases coming out of solution and creating bubbles inside the body during depressurization. Bubbles can form in and migrate to any part of the body causing many different symptoms from joint pain and rashes to blockage of blood supply, paralysis and death. This is called air embolism or arterial gas embolism.
Dysbarism is a term that refers to medical conditions resulting from changes in ambient pressure, including decompression sickness, arterial gas embolism and barotrauma. Ambient pressure refers to pressure of the water around the diver, or the air pressure around caisson workers, pilots and astronauts. For divers, the ambient pressure increases: at 10 meters or about 33 feet in salt water, there is twice the normal pressure at sea level. At 40 meters, the recommended safety limit for recreational diving, the ambient pressure is five times the pressure at sea level.
Pressure decreases above sea level, but much less drastically. At about 1,000 meters (3,000 feet) the ambient pressure is still almost 90 % of that at sea level. At 6,000 meters (20,000 feet) ambient pressure drops to about one-half of sea level pressure.
Air, as a gas, is a very compressible substance. The human body has numerous air spaces and pockets including the sinuses, middle ear, gas in the bowels, cavities and fillings in the teeth, and, by far the largest area—the lungs. At normal atmospheric pressure the pressure within and outside the body is equalized. Barotrauma occurs to airspaces when moving to or from a higher pressure environment. If there is a pressure differential, for example while flying, pain may be experienced in the ear as the higher pressure air within the ear pushes out to the lower pressure in the cabin.
Boyle’s Law defines the relationship between pressure and volume where P and V are inversely proportional. When the volume of gas is reduced the pressure increases. When the volume is increased, the pressure drops. In this way damage occurs in the tissues around the air spaces because gases are compressible and tissues aren’t. During increases in ambient pressure the internal airspace cannot support the surrounding tissues. During decreases the higher pressure of the gas inside causes damage if that gas becomes trapped. The following organs or tissues are easily damaged by barotrauma:
- Middle ear (barotitis or aerotitis)
- Paranasel sinuses (Aerosinusitis)
- Bone (bone necrosis and temporal lobe injury)
- Teeth (causing Barodontalgia: barometric pressure causing dental pain and/or fracture)