Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or in contact with the body, and the surrounding fluid. Barotrauma typically occurs when the organism is exposed to a significant change in ambient pressure, such as when a scuba diver, a free-diver or an airplane passenger ascends or descends, or during uncontrolled decompression of a pressure vessel, but can also be caused by a shock wave. Whales and dolphins are also vulnerable to barotrauma if exposed to rapid and excessive changes in diving pressures. Bats can be killed by barotrauma due to lung damage when flying in low pressure regions close to operating wind turbine blades. 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 diving 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. It is also common for conditions affecting the inner ear to result in auditory hypersensitivity.

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. 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. 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 lungful 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. When diving, the pressure differences which cause the barotrauma are changes in hydrostatic pressure: 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 an amount approximately equal to 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. This pressure change will reduce the volume of a gas filled space by half. Boyle's law describes the relationship between the volume of the gas space and the pressure in the gas. Barotraumas of descent are caused by preventing the free change of volume of the gas in a closed space in contact with the diver, resulting in a pressure difference between the tissues and the gas space, and the unbalanced force due to this pressure difference causes deformation of the tissues resulting in cell rupture. Barotraumas of ascent are also caused when the free change of volume of the gas in a closed space in contact with the diver is prevented. In this case the pressure difference causes a resultant tension in the surrounding tissues which exceeds their tensile strength. Besides tissue rupture, the overpressure may cause ingress of gases into the tissues and further afield through venous blood vessels. Breathing gas at depth from underwater breathing 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 diver who breathes at 10 metres and ascends without exhaling has lungs containing twice the amount of gas at 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 a variety of methods, 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 includes pneumothorax, arterial gas embolism, and mediastinal and subcutanous emphysemas. which are commonly called burst lung or lung overpressure injury by divers. To equalise, all that is necessary is not to hold the breath during ascent. 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. Some people have pathologies of the lung which prevent rapid flow of excess air through the passages, which can lead to lung barotrauma even if the breath is not held during rapid depressurisation. These people should not dive as the risk is unacceptably high. Most commercial or military diving medical examinations will look specifically for signs of this pathology. The air inside the diving mask enclosing the eyes and nose (also known as a half mask). The main risk is bleeding from the capillaries of the eyes from the negative pressure[11] or orbital emphysema from higher pressures. This can be avoided by allowing air into the mask through the nose. Goggles covering only the eyes are not suitable for diving as they cannot be equalised. Air spaces inside a dry suit. The main risk is folds of skin getting pinched inside folds of the drysuit. Most drysuits have a hose connection with a manually operated valve to feed intermediate pressure air in from the cylinder. Air must be manually injected on the descent and is usually automatically vented on the ascent. Following barotrauma of the ears or lungs from diving the diver should not dive again until cleared by a diving doctor. Recovery can take weeks to months. Use of a hyperbaric chamber. Patients undergoing hyperbaric oxygen therapy must learn to equalize in order to avoid barotrauma. Some patients may be at greater risk of otic barotrauma than others. 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. Fish with isolated swim bladders are susceptible to barotrauma of ascent when brought to the surface by fishing. The swim bladder is an organ of buoyancy control which is filled with gas extracted from solution in the blood, and which is normally removed by the reverse process. If the fish is brought upwards in the water column faster than the gas can be resorbed, the gas will expand until the bladder is stretched to its elastic limit, and may rupture. Barotrauma can be directly fatal or disable the fish rendering it vulnerable to predation, but rockfish are able to recover if they are returned to depths similar to those they were pulled up from, shortly after surfacing. Scientists at NOAA developed the Seaqualizer to quickly return rockfish to depth. The device could increase survival in caught-and-released rockfish.

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