Barotrauma is physical damage to body tissues 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 airplane passenger ascends or descends, or during uncontrolled decompression of a pressure vessel. Boyle's law defines the relationship between the volume of the air space and the ambient pressure.

Damage occurs in the tissues around the body's air spaces because gases are compressible and the tissues are not. During increases in ambient pressure, the internal air space provides the surrounding tissues with little support to resist the higher external pressure. During decreases in ambient pressure, the higher pressure of the gas inside the air spaces causes damage to the surrounding tissues if that gas becomes trapped.

Types of injury

Examples of organs or tissues easily damaged by barotrauma are:

• middle ear (barotitis)
• paranasal sinuses (causing Aerosinusitis)
• lungs
• eyes (the unsupportive air space is inside the diving mask)
• skin (when wearing a diving suit which creates an air space)
• bone (bone necrosis and temporal lobe injury)
• Teeth (causing Barodontalgia or dental fractures)

Diving barotrauma

Squeeze

The term 'squeeze' describes the phenomenon of a shrinking air space as the pressure rises and the volume reduces during descent and the pain felt by the diver when this happens. It normally happens in the diving mask and the drysuit.

Lung damage

Most lung pressure damage occurs if the diver holds his breath on ascent, and the high-pressure gas in the lung expands due to decreasing ambient pressure. As the lungs do not sense pain when over-expanded, the diver receives no warning to prevent the injury.

Causes

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

• descending and ascending in water. There are two components to the surrounding pressure acting on the diver: the atmospheric pressure and the water pressure. A descent of 10 metres (33 feet) in water increases the ambient pressure by approximately the pressure of the atmosphere at sea level. So, a descent from the surface to 10 metres (33 feet) underwater results in 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 dive to 10 metres (33 feet) and safely ascend without exhaling, because the gas in the lungs had been inhaled at atmospheric pressure, whereas a SCUBA diver who breathes at 10 metres and ascends without exhaling has lungs containing gas at twice atmospheric pressure and is very likely to suffer life-threatening lung damage.

Equalizing

Diving barotrauma can be avoided by eliminating any pressure differences acting on the tissue or organ by equalizing the pressure. There are a variety of techniques:

• The air spaces in the ears, and the sinuses. The risk is burst eardrum. Here, the diver can use the valsalva manoeuvre, to let air into the middle ears via the Eustachian tubes. Sometimes swallowing will open the Eustachian tubes and equalise the ears. See ear clearing.
• The lungs. The risk is pneumothorax. which is commonly called burst lung by divers. To equalise, always breathe normally and never hold the breath. This risk does not arise when snorkel diving from the surface, unless the snorkeller breathes from a high pressure gas source underwater, or from submerged air pockets.
• The air inside the usual eyes-and-nose diving mask. The main risk is bleeding around the eyes. Here, let air into the mask through the nose. Do not dive in eyes-only goggles as sometimes seen on land with industrial breathing sets.
• Air spaces inside a dry suit. The main risk is folds of skin getting pinched inside folds of the drysuit. Most modern drysuits have a tube connection to feed air in from the cylinder. Air must be injected on the descent and vented on the ascent.

Use of a recompression chamber

Barotrauma and decompression illness are sometimes treated with a recompression chamber, which reproduces the pressure that a person had adjusted to before coming up too quickly to a lower-pressure zone; it allows slow decompression. However, a chamber (if misused) can also cause barotrauma, if the occupant is taken to three or four times atmospheric pressure and quickly returned to lower pressure. This occurs in the Tom Clancy novel Without Remorse.

Blast induced barotrauma

An explosive blast and explosive decompression create a pressure wave that can induce barotrauma. The difference in pressure between internal organs and the outer surface of the body causes injuries to internal organs that contain gas, such as the lungs, gastrointestinal tract, and ear.

Lung injuries can also occur during rapid decompression, although the risk of injury is lower than with explosive decompression.

Ventilator induced barotrauma

Mechanical ventilation can lead to barotrauma of the lungs. This can be due to either:

• absolute pressures used in order to ventilate non-compliant lungs.
• shearing forces, particularly associated with rapid changes in gas velocity.

The resultant alveolar rupture can lead to pneumothorax, pulmonary interstitial emphysema (PIE) and pneumomediastinum.

See also

• Alternobaric vertigo
• Barodontalgia
• Diving hazards and precautions
• Dysbarism
• Jet ventilation
• Uncontrolled decompression

References