Barotrauma

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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. 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.

Diving barotrauma

Types of injury

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

middle ear
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)

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 on ascent where the high-pressure gas in the lung causes it to expand. 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 was 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.

Equalising

Diving barotrauma can be avoided by eliminating any pressure differences acting on the tissue or organ by equalising 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.
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 round 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.

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.