With the onset of the summer vacation come plans for travel, including flying long distances. But the prospect of a long flight often raises health concerns. Especially in passengers who are older or have certain conditions, air travel and the related stress can have an impact on health. Here are a few trouble areas and some precautions you can take.

• Deep vein thrombosis (DVT). Not all experts agree on an association between DVT (blood clots in the legs) and air travel. Symptoms may not occur for several days, so it’s difficult to establish a cause-and-effect relationship. If there is one, it’s likely due to prolonged inactivity. Limited airline space can discourage moving about. Dry cabin air may also increase the risk of DVT.

Prolonged inactivity slows circulation, allowing small clots to form in the legs. The dehydrating effects of cabin air can promote another cause of blood clotting, hemoconcentration, which is an increase in the proportion of red blood cells to plasma (the liquid part of the blood). The body’s own clot busters kick in for most people, but in people with certain risk factors, the clots can be big enough to block a vein. These include cancer, heart disease, infection, pregnancy, and obesity, as well as recent injury or surgery. Smoking also raises the risk, as do birth control pills, selective estrogen receptor modulators, and postmenopausal hormones.

DVT in the calf aches and gets worse over several days. The pain may be accompanied by warmth and swelling in the area around or below the clot. A clot in the thigh or at the junction of the thigh and abdomen causes similar symptoms. The skin may redden or turn bluish. If you experience any of these symptoms, see a doctor; be sure to mention that you’ve recently traveled on a plane.

The biggest danger of DVT is that a clot will break free and lodge in one of the pulmonary arteries supplying blood to the lungs. This potentially fatal condition is called pulmonary embolism. Symptoms include rapid breathing, pain when breathing, shortness of breath, chest pain that travels up to the shoulder, fever, and fainting. It is a medical emergency. Air travelers can do several things to reduce their risk. Here are some ways to reduce air travel-related DVT:

1. If you’re not at risk for bleeding and can tolerate aspirin, take a baby aspirin (81 mgs.) one-half hour before takeoff.

2. Wear loose clothing and comfortable shoes.

3. Avoid crossing your legs while seated.

4. Get up from your seat and walk up and down the aisle at least once an hour. If you’re pregnant, request for an aisle seat so that you can get up easily.

5. Drink at least eight ounces of water every hour or two and avoid alcohol, caffeinated beverages, and salty foods.

6. Keep the space under the seat in front of you empty so you can exercise your feet and ankles occasionally (see illustration).

7. If you have any risk factors for deep vein blood clots, consult your clinician. He/she may suggest support socks or stockings.

• Jet lag. Crossing time zones often leads to jet lag, which can result in headaches, upset stomach and nausea, difficulty concentrating, and trouble sleeping. To help alleviate it, get plenty of sleep before you begin your trip. Keep well hydrated before, during, and after your flight. Change your wristwatch to the new time. As soon as you arrive at your destination, adjust your sleeping and eating schedule to the new time zone. This can be difficult if you’ve crossed many time zones, but try to force yourself to stay awake until the local bedtime, and get up in the morning when the locals do and get outside in the natural light. If you simply cannot stay awake until evening on the day you arrive, nap for no more than an hour or two. Engaging in social activities can also help your body clock adjust. When trying to stay awake, eat protein and vegetables and avoid starchy foods like pastas, breads, and rice.

Most flights, like those of Philippine Airlines to the United States and Canada, leave in the evening and get you to your destination in the afternoon or early evening, which is good since your body will be more or less on its usual schedule when you arrive. Jet lag is less pronounced though, when you travel in the other direction, west, such as when you go to Europe.

• Air quality. A ban on cigarettes has improved air quality on air flights. Modern commercial planes provide a continually recycled mix of fresh air and air recycled from the cabin. The recirculated portion is filtered to trap dust and other particles and microorganisms, including bacteria, fungi, and some viruses. Infectious diseases are sometimes transmitted during air travel, and the effectiveness of filtering systems has been questioned. However, evidence suggests that infection is due to close contact with other passengers rather than contaminated recirculated air. Cabin air, when recycled appropriately, doesn’t appear to pose a health risk.

Because there’s so little moisture at high altitudes, the relative humidity in most commercial aircraft cabins is a low 10 to 20 percent. To combat the drying effect in airways, eyes, and skin, you need to drink plenty of water while flying. You may also want to wear eyeglasses rather than contact lenses, keep a small bottle of natural tears handy, use a nasal saline spray, and use moisturizing lotion on your hands and face.

• Reduced oxygen and air pressure. At cruising altitude, airline cabins have lower-than-normal air pressure and oxygen levels. Blood oxygen saturation during commercial flights can be five- to 10-percent lower than normal. If you’re in good health, your body can compensate, but if you have a lung condition, such as chronic obstructive pulmonary disease, or cardiovascular disease, you may need supplemental oxygen, even if you don’t normally use it. Ask your physician for advice several weeks before your flight.

Airline cabins are pressurized to a level equivalent to the air pressure at 5,000 to 8,000 feet above sea level. If you’re used to lower altitudes, gases trapped inside your body could expand, and that might create problems. Soon after abdominal surgery, for example, the expansion of intestinal gas could cause bleeding or tearing along suture lines. To be safe, consult your physician and plan to wait at least a couple of weeks before flying. And don’t fly within 24 hours of a colonoscopy that involved polyp removal. Gas expansion during air travel can also be a problem for people who’ve recently had facial, eye, or brain surgery.

• Ear pain. During takeoff and landing, cabin air pressure changes rapidly, disturbing the balance of pressure between the outer ear and the middle ear. Many people feel pain when the high pressure stretches the eardrum, the membrane separating the outer and middle ears.

The Eustachian tube, which connects the middle ear to the back of the nose and throat, helps equalize the pressure on the eardrum (and causes the welcome pop you feel when the balance is restored). You can help the process by swallowing, chewing gum, yawning, or opening your mouth wide. A trick called the Valsalva maneuver may also work: Close your nose with your thumb and index finger and exhale gently against a closed mouth. Another option is EarPlanes, special earplugs that even out the pressure on the eardrum.

A FEW EXTRA TIPS FOR AIR TRAVEL

Here are some other things to keep in mind when preparing for a trip:

• If you have diabetes or epilepsy, carry an identification card or small tag from health organizations that certifies that you have the particular medical condition. Also, bring your physician’s name and phone number and a list of your medications.

• If you have a pacemaker or cardioverter-defibrillator, bring a letter from your doctor stating what kind it is and how it’s programmed. You may need this when you go through security.

• If you have an artificial joint or implanted metal of any kind, you may need to show airline or airport security personnel a letter, signed by your doctor, describing its location and purpose.

• Keep all medications in their original containers, in your carry-on bag, so you’ll have them if your luggage is lost or delayed.

• Get to the airport early so you won’t have to run to the terminal. Sudden bursts of physical activity can boost blood pressure and strain the heart.

Have a safe, happy, and healthy trip!

— Sources: Air Travel Health, Harvard Health Publication, May 2004

Healthy Traveling, Mayo Clinic Health Publication, March 2008

— Selected resources: Federal Aviation Administration Office of Aerospace Medicine, www.faa.gov/passengers

International Travel and Health (online edition), World Health Organization, www.who.int/ith