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Traveling by air can cause or worsen a variety of medical conditions, although very few conditions would prevent a person from flying. Those that may prevent flying include a pneumothorax, lung damage from tuberculosis, diseases that could be spread to other passengers, and conditions in which even a small expansion of air would damage tissues, such as intestinal surgery in the previous 10 days. Some conditions require planning and taking precautions before a flight. For example, people who have had a colostomy should wear a large bag and anticipate frequent filling.

Air travel poses problems related to changes in air pressure, reduced amounts of oxygen, turbulence, disruptions of the body's internal 24-hour (circadian) clock (jet lag), and psychologic or physical stress.

Changes in Air Pressure

Modern jet airplanes maintain air pressure inside the cabin (cabin pressure) at low levels, equivalent to the atmospheric pressure at 5,000 to 8,000 feet. At such levels, air trapped in pockets within the body - such as in the lungs, inner ear, sinuses, and intestinal tract - expands by about 25 percent. This expansion sometimes aggravates certain medical conditions, such as emphysema, blocked eustachian tubes, chronic sinusitis, and chronic gas pains. Problems may be particularly severe when an airplane accidentally loses cabin pressure or when the cabin isn't pressurized, as is the case with some smaller airplanes.

A sensation of pressure in the ears is common during airplane flights. It develops as the difference between pressure outside the ear and inside the ear increases, causing the eardrum to bulge. Eventually, the pressure equalizes when the eustachian tube (a passage that connects the middle ear with the back of the nose) allows air to flow in and out of the middle ear. Head colds or allergies may produce fluid and swelling that block the eustachian tube, and repeated infections may result in scarring that partially blocks it. Then air becomes trapped in the middle ear, producing pressure (barotitis media) and pain. Rarely, the eardrum ruptures. Similarly, air may be trapped in the sinuses (barosinusitis), causing facial pain.

Swallowing frequently or yawning during the airplane's descent and taking decongestants before or during the flight can prevent or relieve these conditions. Because children are particularly susceptible to barotitis media, they should chew gum, suck hard candy, or drink something during ascent and descent to encourage swallowing; babies can be nursed or given a bottle or pacifier.

Reduced Oxygen

The relatively low air pressure inside an airplane also causes problems because of its effect on oxygen levels. Low oxygen levels are particularly troublesome for people who have a severe lung disease such as emphysema or cystic fibrosis, heart failure, severe anemia, severe angina, sickle cell disease, or certain congenital heart diseases. Usually, such people can fly safely if provided with oxygen. Airlines can handle a request for oxygen if notified 72 hours in advance of a flight. People generally may fly 10 to 14 days after a heart attack. During flight, people who have breathing problems should not smoke or drink alcohol - which aggravates the effects of reduced oxygen. In general, anyone who can walk 100 yards or climb one flight of stairs should be able to tolerate normal cabin conditions without additional oxygen.

Turbulence

Turbulence can cause air sickness or an injury. People who are prone to air sickness may benefit from dimenhydrinate taken as a tablet or scopolamine applied to the skin as a patch. However, these drugs may cause adverse effects, particularly in the elderly The patches cause fewer adverse effects. To prevent injuries, passengers should keep their seat belts fastened while seated.

Jet Lag

Rapid travel across several time zones produces many physical and psychologic stresses known as jet lag (circadian dysrhythmia). A gradual shift in eating and sleeping patterns before departure may alleviate the problem. Some medication schedules may have to be adjusted; for example, the intervals between drugs normally taken at precise times throughout the day should be based on elapsed time - - such as every 8 hours -rather than on local time. People who have diabetes and who use long-acting insulin may switch to regular insulin until they've adjusted to the new time zone, food, and activity level, or they may make up the difference in time zone changes over several days. They should work out a medication and eating schedule with their doctor before departure and take with them a device to monitor blood sugar (glucose) levels.

Melatonin, a hormone that regulates the sleepwake cycle, is reported to help with sleep disturbances caused by jet lag. Its effectiveness depends on taking the doses on a precise schedule.

Because melatonin products are nutritional supplements rather than prescription drugs, the claims made by the manufacturers have not undergone rigorous scrutiny, and the quality of each formulation may vary.

Psychologic Stress

Fear of flying and claustrophobia can cause distress. Hypnosis and behavior modification help some people. Taking a sedative may relieve fears before and during a flight.

Because the behavior of some mentally ill people worsens during airplane flights, those with violent or unpredictable tendencies must be accompanied by an attendant, and they may need to take a sedative before the flight.

General Precautions

Cardiac pacemakers and metal artificial limbs, plates, or pins are affected by airport metal detectors used to scan for concealed weapons; however, newer models of pacemakers can withstand potential interference from such detectors. To avoid security problems, people who wear such devices should carry a doctor's note explaining the situation.

The risk of developing blood clots in the legs is increased in anyone who sits in one place for a long time. Pregnant women and people who have poor circulation are at particular risk. Walking around the airplane cabin every hour or two and contracting and relaxing the leg muscles while sitting help keep the blood flowing.

Dehydration, resulting from the low humidity (about 5 percent) in the cabin, can be prevented by drinking enough liquids and avoiding alcohol, which makes dehydration worse. People who wear contact lenses should apply rewetting solution to their lenses frequently to combat the effects of dry air.

Special foods, including low-salt, low-fat, and diabetic diets, are usually available from an airline by advance request.

Travelers should pack drugs in a carry-on bag rather than in a suitcase checked at the airport, in case their luggage is lost, stolen, or delayed. Drugs should be kept in their original containers. Travelers who must carry narcotics, large amounts of any drug, or syringes should have a doctor's note to avoid being detained by security or customs officers. Travelers may wish to carry a summary of their medical records, including electrocardiogram results, in case they become ill while away from home. Those who have a potentially disabling condition, such as epilepsy, should wear a Medic Alert identification bracelet or necklace.

Women with normal pregnancies can travel by air through the eighth month. Women with highrisk pregnancies should discuss their travel plans with their doctor and obtain approval before flying. Generally, air travel during the ninth month requires a doctor's note dated within 72 hours of departure and indicating the woman's anticipated date of delivery. Seat belts should be worn low across the thighs, not over the abdomen, to prevent injury to the uterus.

Infants under 7 days old aren't permitted to fly. Children with chronic diseases, such as congenital heart or lung diseases or anemia, have the same restrictions as adults with those conditions. There's no upper age limit for travel.

Airlines make reasonable efforts to accommodate the handicapped. Often, wheelchairs and stretchers can be accommodated on commercial flights; otherwise, air ambulance service is necessary. Some airlines accept people who need special equipment such as intravenous lines and mechanical respirators as long as trained personnel accompany them and arrangements have been made at least 72 hours in advance.

Information and advice about air travel can be obtained from the medical departments of major airlines or from the Federal Aviation Administration Regional Flight Surgeon.

Foreign Travel

Of the millions of people who travel or work abroad every year, about I out of 30 needs medical attention for an illness or injury. Gastrointestinal infections may result from drinking contaminated water, including ice, and beverages or eating uncooked or improperly cooked foods. Casual sexual contacts produce a high risk for contracting the human immunodeficiency virus (HIV), which exists worldwide, as well as other sexually transmitted diseases. Motor vehicle accidents, especially at night, and drowning are the leading causes of death or injury for travelers in foreign countries. Health risks vary according to country and region; the Centers for Disease Control and Prevention provides up-to-date health advisories.

In foreign countries, many insurance plans, including Medicare, are not valid, and hospitals often require a substantial cash deposit, regardless of health insurance held in the United States. A variety of travel insurance plans, including some that arrange for emergency evacuation, are available through travel agents and some credit card companies. Directories listing English-speaking doctors in foreign countries are available from several organizations, and United States consulates may help secure emergency medical services.

Vaccinations

People planning a trip to another country should have the appropriate vaccinations, depending on their destination. In general, more preparation is needed when the trip lasts longer than 3 weeks, has several destinations in developing countries, or involves travel in rural areas or working with resident populations. Requirements for vaccinations change frequently. Some vaccinations must be given 2 to 12 weeks before the trip, so a traveler should inquire about vaccinations in advance. Information about vaccination requirements is available from various sources.

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Excerpted from The Merck Manual Of Medical Information by Robert Berkow Copyright © 1997 by Merck & Co., Inc.
Excerpted by permission. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.