DMT key terms

Any medical condition caused by a change in ambient pressure or by breathing gas at pressure different from the surrounding environment, covering both barotrauma and decompression illness.

Tissue injury produced when a gas-filled space fails to equalise its pressure with the surrounding environment during descent or ascent, such as middle ear or sinus squeeze.

Pressure-related injury occurring on descent when a gas-containing cavity cannot be vented and surrounding tissues are drawn inward, causing pain, oedema or haemorrhage.

The channel connecting the middle ear to the nasopharynx that normally allows gas to move in and out so middle-ear pressure can balance with ambient pressure.

Tearing of the eardrum caused by a large pressure gradient across it, typically after forceful descent with blocked equalisation, producing sudden pain and hearing loss.

Brief spinning sensation caused by unequal pressure or gas volumes between the two middle ears, usually during ascent, which can disorient a diver underwater.

Lung injury from over-distension and alveolar rupture when gas trapped in the lungs expands during ascent, allowing gas to escape into tissue or the circulation.

Gas bubbles entering the arterial circulation, most often from ruptured alveoli after a rapid ascent, obstructing small vessels and causing sudden neurological or cardiac symptoms.

Air in the pleural space that separates lung from chest wall and can collapse the lung; in diving it may follow pulmonary barotrauma or a ruptured bulla.

Progressive air accumulation in the pleural space that shifts mediastinal structures and impairs venous return, causing severe respiratory and circulatory compromise requiring urgent decompression.

Illness caused by inert gas coming out of solution as bubbles in tissues or blood after a reduction in ambient pressure, producing joint pain, skin, neurological or cardiorespiratory signs.

An umbrella clinical term covering both decompression sickness and arterial gas embolism, since the two often cannot be distinguished at the bedside and are managed similarly.

The quantity of dissolved nitrogen or other inert gas taken up by body tissues during a dive, determined by depth, time and tissue perfusion, and released during ascent.

The state in which tissues have taken up as much inert gas as they can at a given pressure, so further exposure at that depth adds no more dissolved gas.

The period a theoretical tissue compartment needs to take up or release half the inert gas difference toward equilibrium, used in decompression models to schedule safe ascents.

A planned pause at a specified depth during ascent that allows inert gas to be eliminated gradually so bubbles do not form in tissues or blood.

The speed at which a diver moves toward the surface, usually limited to about 9 to 10 metres per minute, to keep bubble formation within tolerable limits.

Reversible impairment of judgement, coordination and mood caused by breathing nitrogen at raised partial pressure, typically noticed below about 30 metres of seawater.

Harmful effects of breathing oxygen at high partial pressure, presenting as acute central nervous system seizures underwater or as lung irritation and fibrosis with prolonged exposure.

Lung injury from prolonged exposure to raised oxygen partial pressure, causing tracheal irritation, cough and reduced vital capacity that resolves slowly after exposure ends.

The pressure a single gas in a mixture would exert if it occupied the whole volume, calculated as fraction of gas multiplied by total ambient pressure.

Insufficient oxygen reaching tissues, in diving caused by low inspired oxygen partial pressure, gas contamination, breath-hold ascent or equipment failure.

Loss of consciousness during a breath-hold ascent, when expanding lung gas lowers oxygen partial pressure below the level needed to sustain awareness before the diver reaches the surface.

Breathing faster or deeper than metabolic need, which lowers carbon dioxide and can remove the urge to breathe, increasing the risk of blackout during breath-hold diving.

Fluid accumulation in the lungs during immersion or swimming, causing breathlessness, cough and low oxygen, seen in otherwise healthy divers and often recurring on later dives.

Treatment in which a patient breathes pure oxygen inside a chamber at pressure greater than one atmosphere, raising dissolved oxygen and helping ischaemic or infected tissues.

A prescribed schedule of chamber pressure, breathing-gas switches and timings used to treat a specific condition, such as a US Navy Table 6 for decompression illness.

A pressure vessel, either monoplace for one patient or multiplace for several with an attendant, in which hyperbaric oxygen therapy or recompression is delivered.

A trained person who enters a multiplace chamber with patients to provide direct care, monitor breathing gas and assist with emergencies during treatment.

Hyperbaric recompression that shrinks bubbles and improves perfusion, given as early as possible for arterial gas embolism or severe decompression illness.

Non-invasive measurement of skin oxygen tension using heated electrodes, used to assess tissue perfusion and to guide or evaluate hyperbaric oxygen therapy.

The temporary increase in oxygen partial pressure and decrease in inert gas partial pressure in blood after switching to pure oxygen, aiding inert gas elimination.

Returning a patient to raised ambient pressure, usually in a chamber with oxygen, to reduce bubble size and restore circulation in decompression illness.

A systematic inspection of equipment, gas supply and personal fitness before entering the water, intended to catch faults while they can still be corrected safely.

A mutual verification between paired divers that each has adequate gas, working regulators and correct configuration before the dive begins.

A documented schedule of maximum depth, bottom time, gas requirements, ascent profile and contingency options agreed before a dive to keep exposure within limits.

The volume of breathing gas kept aside for ascent, safety stops and emergencies, never used for bottom time, often calculated as a third of the supply.

A float deployed by divers to show their position to boat traffic and to indicate the ascent line, improving separation from surface hazards.

The set of design, testing and inspection rules a hyperbaric chamber must meet to ensure it can safely contain pressurised gas and oxygen-enriched atmospheres.

Measures controlling oxygen concentration, ignition sources and flammable materials inside a chamber, since raised oxygen pressure makes fire spread rapidly and burn intensely.

A formal assessment of a diver's physical and mental suitability for diving, covering conditions that risk barotrauma, loss of consciousness or impaired judgement underwater.

The legal and ethical obligation of instructors, supervisors and operators to protect divers and patients from foreseeable harm through planning, training and adequate supervision.