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.
Ear barotrauma
Barotrauma can affect the external, middle, or inner ear. Middle ear barotrauma (MEBT) is the most common being experienced by between 10% and 30% of divers and is due to insufficient equilibration of the middle ear. External ear barotrauma may occur on ascent if high pressure air is trapped in the external auditory canal either by tight fitting SCUBA equipment or ear wax. Inner ear barotrauma (IEBT) though much less common than MEBT shares a similar mechanism. Mechanical trauma to the inner ear can lead to varying degrees of conductive and sensorineural hearing loss as well as vertigo.
Barosinusitis
The sinuses similar to other air filled cavities are susceptible to barotrauma if their openings become obstructed. This can result in pain as well as epistaxis.
Mask squeeze
If a diver's mask is not equalized during descent the relative negative pressure can produce petechial hemorrhages in the area covered by the mask along with subconjunctival hemorrhages.
Pulmonary barotrauma
Pulmonary (lung) pressure damage in scuba divers is usually caused by breath-holding on ascent. The compressed gas in the lungs expands as the ambient pressure decreases causing the lungs to over expand and rupture unless the diver breathes out. The lungs do not sense pain when over-expanded giving the diver little warning to prevent the injury. This does not affect breath-hold skin divers as they bring a lungfull of air with them from the surface, which merely re-expands safely to near its original volume on ascent. The problem only arises if a breath of compressed gas is taken at depth, which will then expand on ascent to more than the lung volume. Pulmonary barotrauma may also be caused by explosive decompression of a pressurised aircraft.
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.
Avoidance and treatment
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 from the negative pressure[10] or orbital emphysema from higher pressures. 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.
Following barotrauma of the ears or lungs from diving the diver should not dive again until thoroughly cleared by a doctor, which can take many months.
Thanks to Wikipedia, the free encyclopedia
Kathy Dowsett
www.kirkscubagear.com
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