ABEM UHM key terms

At constant temperature, the volume of a fixed mass of gas is inversely proportional to its absolute pressure. Explains barotrauma on descent and gas expansion during ascent.

The amount of gas dissolved in a liquid at equilibrium is proportional to the partial pressure of that gas above the liquid. Underlies inert gas loading, decompression sickness, and oxygen toxicity.

The total pressure of a gas mixture equals the sum of the partial pressures of its component gases. Used to compute inspired oxygen and nitrogen partial pressures at depth.

At constant pressure, gas volume is directly proportional to absolute temperature. Explains pressure changes in closed spaces as temperature varies, such as in a sealed cylinder.

The pressure exerted by a single gas in a mixture, equal to its fraction of the mixture times the total absolute pressure. Determines physiologic effect of oxygen and inert gases at depth.

Total pressure measured relative to a vacuum, including atmospheric pressure. At sea level approximately one atmosphere; increases by one atmosphere for roughly every 10 meters of seawater.

Pressure measured relative to ambient atmospheric pressure, so it reads zero at the surface. Depth gauges and tank pressures are typically displayed as gauge values.

The total surrounding pressure at a given location, such as at depth underwater or inside a hyperbaric chamber. Drives gas volume and dissolved gas changes in divers and patients.

Tissue injury caused by a pressure difference between a gas-filled space and its surroundings when the space cannot equalize. Common sites include middle ear, sinuses, lung, and mask.

Barotrauma of the middle ear from failure to equalize pressure across the tympanic membrane during descent. Causes ear pain, muffled hearing, and possible hemotympanum or membrane rupture.

Tear of the round window membrane from pressure imbalance, often with forceful Valsalva or barotrauma. Produces sudden vertigo, sensorineural hearing loss, and tinnitus; a perilymphatic fistula may result.

Alveolar rupture from lung overexpansion during ascent with a closed glottis or breath-holding. Can force gas into tissue, causing pneumothorax, pneumomediastinum, or arterial gas embolism.

Entry of gas bubbles into the arterial circulation, usually from pulmonary overexpansion, causing abrupt neurologic or cardiac ischemia within minutes of surfacing. A decompression illness emergency.

Illness from inert gas bubbles forming in tissues or blood after pressure reduction. Type 1 involves joints and skin; Type 2 involves neurologic, pulmonary, or cardiovascular systems.

An umbrella term covering both decompression sickness and arterial gas embolism, since the two can be difficult to distinguish clinically and share hyperbaric oxygen treatment.

Accumulation of dissolved nitrogen or other inert gas in tissues during exposure to elevated pressure. The gradient and tissue half-times determine subsequent bubble risk on ascent.

A planned pause during ascent allowing dissolved inert gas to be eliminated gradually so that bubble formation is minimized. Depth and duration derive from dive tables or computers.

A short, usually three-to-five minute pause at shallow depth near the end of a recreational dive. It is not mandatory decompression but reduces bubble formation risk.

Reversible impairment of judgment, coordination, and cognition from breathing nitrogen at elevated partial pressure, typically noticed below about 30 meters. Resolves with ascent.

Harmful effects of elevated oxygen partial pressure. Acute pulmonary and central nervous system toxicity occur at depth; chronic pulmonary toxicity occurs with prolonged hyperbaric or high-dose exposure.

Breathing 100 percent oxygen at greater than one atmosphere absolute inside a pressurized chamber. Used for decompression illness, carbon monoxide poisoning, and selected wound and radiation injuries.

A defined hyperbaric chamber pressure-time profile specifying depth, oxygen breathing periods, and air breaks. United States Navy tables are commonly used for decompression illness.

A scheduled interval of breathing chamber air instead of oxygen during hyperbaric treatment. Reduces cumulative oxygen dose and risk of pulmonary and central nervous system oxygen toxicity.

A hyperbaric chamber sized for one patient, usually pressurized with oxygen so the patient need not wear a mask. Limits attendant access and some equipment compatibility.

A hyperbaric chamber accommodating several people, including inside attendants, who breathe oxygen by mask or hood. Allows direct patient care during treatment.

A trained person who accompanies patients inside a multiplace chamber to provide care. Requires fitness screening and has its own decompression exposure and risk.

Tissue hypoxia from carbon monoxide binding hemoglobin and cytochrome enzymes. Hyperbaric oxygen accelerates elimination and is considered for severe poisoning, syncope, or neurologic or cardiac involvement.

Venous air entry through catheters can reach the arterial circulation via a patent foramen ovale or pulmonary capillary transit, mimicking diving arterial gas embolism and warranting hyperbaric oxygen.

Risk of pulmonary overexpansion in a ventilated or breath-holding patient during chamber depressurization. Requires airway patency and controlled exhalation during ascent.

Vestibular and cochlear symptoms from inert gas bubbles in the inner ear after diving, often with a patent foramen ovale. Distinguished from inner ear barotrauma, which may contraindicate recompression.

A persistent opening between the atria present in roughly a quarter of adults. Permits right-to-left shunting of venous bubbles, increasing risk of arterial embolism and some decompression illness.

Noncardiogenic pulmonary edema during or after immersion, especially in cold water or with exertion. Presents with dyspnea, cough, and hypoxemia; treated with oxygen, rest, and diuresis if needed.

Exposure to cold water causing rapid heat loss, peripheral vasoconstriction, and risk of hypothermia and arrhythmia. Influences gas uptake and can precipitate immersion pulmonary edema.

Core body temperature below normal from heat loss exceeding production, common in divers. Impairs consciousness and coordination and complicates resuscitation and rewarming.

Respiratory impairment from submersion or immersion in liquid, historically classified as wet or dry. Management emphasizes early rescue breathing, oxygenation, and treatment of aspiration and hypothermia.

Tissue damage from gas expanding in a confined space as ambient pressure falls, such as during ascent. Prevented by allowing gas to escape from lungs and other closed spaces.

Transient vertigo from unequal pressure or gas volumes between the two middle ears during pressure change. Resolves with equalization; can impair safety underwater.