Barotrauma

Barotrauma is physical damage to body tisses caused by a difference in pressure between an air space inside or beside the body and the surrounding gas or liquid.

Barotrauma typically occurs to air spaces within a body when that body moves to or from a higher pressure environment, such as when a SCUBA diver, a free-diving diver or an aeroplane passenger ascends or descends.

The reason that barotrauma occurs in body spaces is that gases are compressible, so, they provide the air space with little support to resist a difference between the internal and external pressure. Boyle's law defines the relationship between the volume of the air space and the ambient pressure.

Diving barotrauma

Examples of organs or tissues easily damaged by barotrauma due to diving are:

• middle ear
• paranasal sinuses
• lungs
• eyes (the air space is inside the diving mask)

The term 'squeeze' describes pain on descent and affects the ears, sinuses, eyes and the skin. Lung pressure damage normally only occurs on ascent where the high pressure gas in the lung causes it to expand. One of the reasons lung damage happens is the lungs do not sense pain during when over-expanded.

When diving the pressure differences needed to cause the barotrauma come from two sources:

• descending and ascending in water. A descent from the surface to 10 metres / 33 feet underwater results is a doubling of the pressure on the diver
• breathing gas at depth from SCUBA equipment results in the lungs containing gas at a higher pressure than atmospheric pressure. So a free-diving diver can safely ascend from 10 metres without exhaling because the gas in the lungs was inhaled at atmospheric pressure, whereas a SCUBA diver who does not exhale on an ascent from 10 metres, with lungs containing gas at twice atmosperic pressure, is very likely to suffer life threatening lung damage.

Diving barotrauma can be avoided by eliminating any pressure differences acting on the tissue or organ by equalising the pressure. The Valsalva manoeuvre can be used to equalise the ears. Regular and frequent breathing can help equalise the lungs. Exhaling into the mask can equalise the pressure inside the mask to avoid squeeze.