DAN Medical Frequently Asked Questions

Back to Medical FAQ List


Definitions to the terms you may encounter while researching travel-related health matters in preparation for a trip, or while handling such matters during your travels.Here are definitions of some of the terms you may encounter while researching travel-related health matters in preparation for a trip, or while handling such matters during your travels.

Afterdrop: A continued decline in the body's core temperature, even after a hypothermic patient has been rewarmed.

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 the process of gas exchange (the intake of oxygen and the 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 (though AGE can also affect the lungs or other organs); typical signs and symptoms include a rapid onset of stroke-like symptoms, within less than 15 minutes after 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; it is 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, since 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, it results in immediate cessation of the heartbeat and the circulation of blood, and, unless it's reversed, in a loss of breathing and consciousness. Cardiac arrest, which is different from a heart attack, is often caused by a disturbance in the heart's electrical system. See also "heart attack."

Conjunctival suffusion: Redness of the conjunctiva, the mucous membrane that covers the eye; it is 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, which supply the heart itself 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). DCI is 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. The 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. DCS is also referred to as "the bends."

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 hypotension (low blood pressure).

Edema: An accumulation of excess fluid in any of the body's tissues or cavities.
Enriched-air nitrox (EAN): A nitrogen-oxygen breathing gas mixture containing more than 21 percent oxygen, usually made by mixing air with extra oxygen; it is also known as oxygen-enriched air.

Heart attack: Also known as a myocardial infarction, a heart attack is a sudden blockage of the flow of blood within the heart itself, usually due to a blood clot in one of the coronary arteries, which supply the heart itself with blood — a condition known as coronary thrombosis; a heart attack often results in damage to the heart muscle and can be fatal.

Hyperthermia: A condition in which the body's core temperature is elevated above normal; the effects of hyperthermia, which range from edema to syncope, 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; the effects of hypothermia, which range from shivering and fatigue to hallucinations and loss of consciousness, 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 (Lpm): A unit used to measure the flow rate of a gas or liquid.

Mediastinum: A membranous partition between two cavities in the body or two parts of an organ. The term is most often used to refer to a space within the chest located between the lungs; it contains the heart, the major blood vessels, the trachea (also known as the windpipe), and the esophagus (the tube that connects the throat to the stomach).

Mediastinal emphysema (also known as pneumomediastinum): A condition characterized by gas bubbles trapped within the mediastinum; see also "mediastinum." This is usually the result of pulmonary barotrauma, but it can also occur as a result of perforation of the esophagus, stomach or intestine.

Myalgia: Muscle pain.

Myocardial infarction: See "heart attack."

No-decompression dive (also known as a no-stop dive): A dive after which direct ascent to the surface at a rate of 30 to 60 feet of sea water per minute (9 to 18 meters of sea water per minute) is allowed at any time during the dive, without a decompression stop.

Nystagmus: Involuntary, rapid, rhythmic movement of the eyes; it can be a symptom of certain pressure-related disorders.

Oxygen: A colorless, odorless gas essential to life; it 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. Oxygen toxicity 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 an injection.

Pneumomediastinum: See "mediastinal emphysema."

Pneumothorax: The presence of air or other gases in the chest cavity, outside the lungs; it 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. It can be a complication of breathing compressed air while diving, as well as of receiving supplemental oxygen therapy, and 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 "pneumotherax."

Rapid ascent: An ascent rate fast enough to put a diver at risk of decompression illness — usually a rate in excess of 60 feet of sea water per minute (18 meters of sea water per minute).

Recovery position: A first-aid technique for positioning patients who are unconscious or injured but breathing; they are placed lying on their side, leaning slightly forward, in what is also called a semi-prone or a three-quarters prone position. This helps to keep their airway clear if they begin to vomit.

Respiratory arrest: The cessation of normal breathing. It is often caused by cardiac arrest, but there can be other causes for respiratory 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. See also "cardiac arrest."

Sign: An objective indication of illness or injury that can be detected by a doctor, such as temperature or pulse.

Supine: Lying flat on the back, face up.

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

Syncope: Fainting, or a temporary loss of consciousness.

Other Features FAQs