In divers<unk>  may be caused when diving, either from being crushed, or squeezed, on descent or by stretching and bursting on ascent; both can be avoided by equalising the pressures. A negative, unbalanced pressure is known as a squeeze, crushing eardrums, dry suit, lungs or mask inwards and can be equalised by putting air into the squeezed space. A positive unbalanced pressure expands internal spaces rupturing tissue and can be equalised by letting air out, for example by exhaling. Both may cause<unk> . There are a variety of techniques depending on the affected area and whether the pressure inequality is a squeeze or an expansion: * Ears and sinuses: There is a risk of stretched or burst eardrums, usually crushed inwards during descent but sometimes stretched outwards on ascent. The diver can use a variety of methods to let air into or out of the middle ears via the Eustachian tubes. Sometimes swallowing will open the Eustachian tubes and equalise the ears. * Lungs: There is a risk of pneumothorax, arterial gas embolism, and mediastinal and subcutaneous emphysema during ascent, which are commonly called burst lung or lung overpressure injury by divers. To equalise the lungs, all that is necessary is not to hold the breath during ascent. This risk does not occur when breath-hold diving from the surface, unless the diver breathes from an ambient pressure gas source underwater; breath-hold divers do suffer squeezed lungs on descent, crushing in the chest cavity, but, while uncomfortable, this rarely causes lung injury and returns to normal at the surface. Some people have pathology of the lung which prevent rapid flow of excess air through the passages, which can lead to lung<unk>  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. * Diving mask squeeze enclosing the eyes and nose: The main risk is rupture of the capillaries of the eyes and facial skin because of the negative pressure difference between the gas space and blood pressure, or orbital emphysema from higher pressures. This can be avoided by breathing air into the mask through the nose. Goggles covering only the eyes are not suitable for deep diving as they cannot be equalised. * Dry suit squeeze. The main risk is skin getting pinched and bruised by folds of the dry suit when squeezed on descent. Most dry suits can be equalised against squeeze via a manually operated valve fed from a low pressure gas supply. Air must be manually injected during the descent to avoid squeeze and is manually or automatically vented on the ascent to maintain buoyancy control. * Diving helmet squeeze: Helmet squeeze will occur if the gas supply hose is severed above the diver and the non-return valve at the helmet gas inlet fails or is not fitted. Severity will depend on the hydrostatic pressure difference. A very rapid descent, usually by accident, may exceed the rate at which the breathing gas supply can equalise the pressure causing a temporary squeeze. The introduction of the non-return valve and high maximum gas supply flow rates have all but eliminated both these risks. In helmets fitted with a neck dam, the dam will admit water into the helmet if the internal pressure gets too low; this is less of a problem than helmet squeeze but the diver may drown if the gas supply is not reinstated quickly. This form of<unk>  is avoidable by controlled descent rate, which is standard practice for commercial divers, who will use shotlines, diving stages and wet bells to control descent and ascent rates. Medical screening Professional divers are screened for risk factors during initial and periodical medical examination for fitness to dive. In most cases recreational divers are not medically screened, but are required to provide a medical statement before acceptance for training in which the most common and easy to identify risk factors must be declared. If these factors are declared, the diver may be required to be examined by a medical practitioner, and may be disqualified from diving if the conditions indicate. Asthma, Marfan syndrome, and COPD pose a very high risk of pneumothorax. In some countries these may be considered absolute contraindications, while in others the severity may be taken into consideration. Asthmatics with a mild and well controlled condition may be permitted to dive under restricted circumstances. Training A significant part of entry level diver training is focused on understanding the risks and procedural avoidance of<unk> . Professional divers and recreational divers with rescue training are trained in the basic skills of recognizing and first aid management of diving<unk> . In mechanical ventilation Isolated mechanical forces may not adequately explain ventilator induced lung injury (VILI). The damage is affected by the interaction of these forces and the pre-existing state of the lung tissues, and dynamic changes in alveolar structure may be involved. Factors such as plateau pressure and positive end-expiratory pressure (PEEP) alone do not adequately predict injury. Cyclic deformation of lung tissue may play a large part in the cause of VILI, and contributory factors probably include tidal volume, positive end-expiratory pressure and respiratory rate. There is no protocol guaranteed to avoid all risk in all applications.
Barotrauma
Blast injury
Polytrauma
Rheotrauma
Penetrating trauma
Microtrauma
Trauma
Blunt trauma