Glossary

Glossary

The following are definitions of some terms you may encounter while researching travel-related health matters.

afterdrop: a continued decline in the body’s core temperature, even after a hypothermic patient has been warmed

alternobaric vertigo: extreme dizziness and disorientation resulting from unequal pressure in the left and right middle ears (Failure to equalize symmetrically, typically during ascent after a dive, can cause the brain to erroneously perceive the difference as movement.)

alveoli: the tiny air sacs in the lungs where gas exchange (intake of oxygen and elimination of carbon dioxide) takes place

antihistamine: a drug that inhibits natural compounds called histamines, which are released by the body’s cells during allergic and inflammatory responses (Antihistamines are typically used to treat allergies and colds; some can cause drowsiness.)

arterial gas embolism (AGE): a condition in which dissolved gases come out of solution and form bubbles in the arterial circulatory system (AGE is often caused by a sudden reduction in ambient pressure, such as during a rapid ascent without exhalation. The organ most often affected is the brain, although AGE can also affect the lungs or other organs. Typical signs and symptoms include a rapid onset of stroke-like symptoms within 15 minutes of reaching the surface.)

barotrauma: any injury, typically of the ears or lungs, caused by a differential between the ambient pressure and the pressure in a gas-filled space in the body (If gas is trapped in a closed space, it will be compressed if the ambient pressure increases — such as during the descent phase of a dive — and will expand if the ambient pressure decreases — such as during ascent. Barotrauma injuries of descent include ear squeeze, tympanic membrane rupture and sinus squeeze. Injuries of ascent include pulmonary barotrauma, which can result in air embolism, pneumothorax and pneumomediastinum.)

carbon dioxide: an odorless, colorless gas produced as a waste product by the metabolism of oxygen in the body’s cells; returned to the lungs through the venous blood system and then exhaled

carbon monoxide: a highly poisonous, odorless, colorless gas that’s a product of incomplete combustion (Carbon monoxide is toxic when inhaled because it competes with oxygen in binding to hemoglobin in the blood, resulting in diminished availability of oxygen for the body’s tissues.)

cardiac arrest: a sudden though sometimes temporary cessation of the heart’s function; also known as cardiopulmonary arrest; see also heart attack (It results in immediate cessation of the heartbeat, blood circulation and, unless reversed, breathing and consciousness. Cardiac arrest, which is different from a heart attack, is often caused by a disturbance in the heart’s electrical system.)

conjunctival suffusion: redness of the conjunctiva, the mucous membrane that covers the eye; often caused by infection with bacteria of the Leptospira genus

coronary thrombosis: a blockage in the flow of blood to the heart due to a blood clot in one of the coronary arteries that supply the heart with blood; see also heart attack

cyanosis: a bluish discoloration of the skin and the body’s mucous membranes due to inadequate oxygenation of the blood

decompression illness (DCI): a broad term that encompasses both decompression sickness (DCS) and arterial gas embolism (AGE); commonly used to describe any systemic disease caused by a reduction in ambient pressure (The signs and symptoms of DCS and AGE can be similar, and recompression is the treatment for both.)

decompression sickness (DCS): a syndrome caused by inert gases coming out of solution in the body and forming bubbles in the tissues and the bloodstream during or after a sudden ascent from a compressed-gas dive; also referred to as “the bends” (Symptoms may include itching, rash, joint pain, muscle aches or sensory changes such as numbness and tingling. More serious symptoms include muscle weakness, paralysis or disorders of the higher cerebral functions, including memory and personality changes.)

dehydration: depletion of the body’s water reserves to a level below normal, caused by giving off more water — through excretion, breathing or sweating — than is taken in (Mild dehydration may go unnoticed; more severe dehydration can cause dizziness, rapid heartbeat and low blood pressure.)

edema: an accumulation of excess fluid in any of the body’s tissues or cavities

heart attack: a sudden blockage of the flow of blood within the heart, usually due to a blood clot in one of the coronary arteries; also known as a myocardial infarction (A heart attack often results in damage to the heart muscle and can be fatal.)

hyperoxia: excessive oxygen supply to the body

hyperthermia: a condition in which the body’s core temperature is elevated above normal; effects range from edema to syncope and can be seen beginning at 104°F (40°C)

hypoglycemia: a condition in which one’s blood glucose (blood sugar) is lower than normal

hypothermia: a condition in which the body’s core temperature drops below normal; effects range from shivering and fatigue to hallucinations and loss of consciousness and can be seen beginning at 95°F (35°C)

hypoxia: an inadequate supply of oxygen to the body tissues

initial assessment: a first responder’s initial evaluation of ill or injured patients, especially of their breathing and circulation, to evaluate any immediate threats to their lives

liters per minute (L/min): a unit used to measure the flow rate of a gas
or liquid

mediastinal emphysema: a condition characterized by gas bubbles trapped within the mediastinum; usually the result of pulmonary barotrauma but can also occur as a result of perforation of the esophagus, stomach or intestine; also known as pneumomediastinum; see also mediastinum

mediastinum: a membranous partition between two cavities in the body or two parts of an organ; most often refers to a space within the chest located between the lungs and containing the heart, the major blood vessels, the trachea (windpipe) and the esophagus

myalgia: muscle pain

myocardial infarction: see heart attack

no-decompression dive: a dive after which direct ascent to the surface at a rate of 30 to 60 feet (9 to 18 meters) of seawater per minute is allowed at any time during the dive without a decompression stop; also called a no-stop dive

nystagmus: involuntary, rapid, rhythmic movement of the eyes; can be a symptom of certain pressure-related disorders

oxygen: a colorless, odorless gas essential to life; makes up approximately 21 percent of the Earth’s atmosphere at sea level

oxygen toxicity: a condition caused by breathing oxygen at a pressure greater than normal atmospheric pressure, such as from a diver’s compressed-air tank; primarily affects the central nervous system and the lungs (The latter effects, known as pulmonary oxygen toxicity, are caused by inflammation of the lung tissue, resulting in shortness of breath, cough and a reduced ability to perform exercise.)

parenteral: introduced into the body by a means other than through the mouth and digestive tract, such as by an injection

pneumomediastinum: see mediastinal emphysema

pneumothorax: the presence of air or other gases in the chest cavity, outside the lungs; can cause the collapse of one or
both lungs

pulmonary edema: an accumulation of excess fluid in the lungs

pulmonary overexpansion: abnormal distension or enlargement of the lungs; can be a complication of breathing compressed air while diving as well as of receiving supplemental oxygen therapy; can cause rupture of the alveoli and penetration of gas into surrounding spaces, causing mediastinal emphysema, pneumothorax or an arterial gas embolism; see also alveoli, arterial gas embolism, mediastinal emphysema and pneumothorax

rapid ascent: an ascent rate fast enough to put a diver at risk of decompression illness — usually a rate of more than 60 feet (18 meters) of seawater per minute

recovery position: a first aid technique for positioning patients who are unconscious or injured but breathing to help keep their airway clear if they begin to vomit; placement is lying on their side and leaning slightly forward in what is also called a semiprone or a three-quarters prone position

respiratory arrest: the cessation of normal breathing, often caused by cardiac arrest; see also cardiac arrest (Once breathing ceases, the body is no longer taking in oxygen for delivery to the body’s tissues. If the condition isn’t reversed in a few minutes, it results in unconsciousness and death.)

sign: an objective indication of illness or injury, such as temperature or pulse, that can be detected by a doctor

supine: lying flat on the back, face up

symptom: a subjective indication of illness or injury, such as pain or fatigue, that can be detected by a patient

syncope: fainting or a temporary loss of consciousness

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