Simple exercises help prevent deep-vein thrombosis

Q: My 61-year-old mother plans to take a 12-hour plane trip in the near future. Her legs usually get swollen when she flies a long distance. So far, this swelling has been harmless, but I'm worried that on such a long flight, she might get a blood clot in her leg. Is there anything special she can do to prevent this from happening?

A: Many people develop mild swelling in their feet, ankles and lower legs during long-haul flights. Sitting still is the culprit; without the pumping action of contracting leg muscles, blood and fluid accumulate in the lower extremities.

The swelling itself is benign, though it can be plenty annoying, especially when you try to put your shoes back on at the end of the flight. But swelling can signal complications, especially when it's more prominent in one leg than the other.

The big worry on a long-haul flight is the development of a blood clot, also known as deep-vein thrombosis (DVT). These clots can cause long-lasting problems in the affected leg. And if the clot breaks away and travels in the bloodstream to an artery in the lungs (this is called pulmonary embolism), it can cause chest pain and breathing problems. A large embolism can even cause sudden death.

Our veins are thin-walled blood vessels that depend on the skeletal muscles around them to regulate blood flow. Veins are less complicated than arteries, but they have an elegant design of their own. In fact, this anatomy is particularly important for the leg veins. These veins have the challenge of carrying blood back up to your heart, whether you are reclining in bed or standing upright.

Veins have a series of one-way valves that allow blood to flow toward the heart while preventing backflow. The leg veins rely on contractions of the leg muscles to counter the force of gravity and propel blood to the heart.

Leg veins are by far the most vulnerable to DVTs and other venous disorders. There are three types of leg veins. The superficial veins lie close to the skin; the deep veins are located deep in the muscles; and the perforator veins connect the other two systems, with blood normally flowing from the superficial to the deep veins, which carry more than 80 percent of the blood that flows from the legs to the heart.

Although venous clots can sometimes form without an obvious cause, the majority of DVTs are triggered by one of three conditions: slowed flow of blood, a boost in the activity of the blood's clotting system, or an injury to the vein wall.

Why does travel increase the risk of DVTs? Any form of prolonged sitting can trigger DVTs, but air travel compounds the problem because of its cramped quarters and dry air, which makes the blood "thicker" and "stickier."

Wearing below-the-knee vascular compression stockings that exert a small amount of pressure can prevent or diminish the swelling. Look for a pair that applies pressure of 20 to 30 millimeters of mercury (mm Hg). They are available at hospitals and large drugstores. Passengers who have significant problems with arteries or nerves in their legs should check with their doctors first.

Keeping mobile is also very important. If possible, have your mother sit in an exit row, bulkhead or aisle seat to give her more legroom. She should avoid crossing her legs. Stretching, massaging her lower legs and pumping her feet up and down for about 30 seconds every 30 minutes can help. She should take a walk in the aisle at least once every hour or so. In-seat exercises, involving contraction of the calf muscles or wiggling the feet up and down in rapid repetition, may be helpful in promoting circulation from the legs.

Another important way to prevent DVT is to stay well hydrated. Your mother should drink lots of non-alcoholic beverages; she'll know she's getting enough when she finds herself making frequent trips to the toilet. Getting up to go to the lavatory also increases circulation in the lower legs and exercises the calf muscles. Alcohol, which dehydrates, should be limited or avoided entirely.

Some clinicians advocate taking aspirin, but it provides only modest protection against DVTs. An injection of low-molecular-weight heparin is much more effective, but doctors usually reserve this prescription medication for people at high risk, such as those with prior DVTs.

Air travel is a hassle these days, but simple precautions can help keep leg swelling and blood clots from making a long flight into a medical emergency.

Submit questions to harvard_adviser@hms.harvard.edu.