DVT can be life-threatening

Q: I often fly from coast to coast on business. On my last flight, my seatmate expressed concern about deep-vein thrombosis, but I thought that only happens after surgery. Should I be worried?

A: Many venous disorders are mild, but some are serious. Deep-vein thrombosis (DVT), the formation of a blood clot in a vein, is a major concern for hospitalized patients, but it can also strike people like you who are immobile for long periods of time while traveling. And it can be life-threatening.

Veins collect blood from the tissues and return it to your lungs, where it picks up oxygen before the heart pumps it out to all your organs. Unlike arteries, which have the ability to relax and contract on their own to regulate blood flow, veins rely on the skeletal muscles around them to contract and propel blood toward the heart. They also have a series of one-way valves that prevent blood from flowing backward, or down toward your feet.

Leg veins, particularly those in the calf, are the most vulnerable to DVT. (DVTs in the arms are relatively uncommon.) There are three types of leg veins: Superficial veins lie close to the skin; the deep veins are deep in the muscles; and the perforator veins connect the two. The deep veins carry more than 80 percent of the blood that flows from the legs to the heart.

Although clots can form without an obvious cause, most cases of DVT 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 a vein. The risk of DVT increases with surgery, especially on the hips or knees; sitting still for long periods, such as on a cross-country flight; prolonged bed rest; leg paralysis; strokes; heart failure; trauma; smoking; obesity; blood-clotting abnormalities; some medications; and widespread cancer.

Symptoms of DVT include calf pain, calf tenderness and leg swelling. In most cases, only one leg is affected. The calf can feel tense and swollen, and the foot and ankle may be puffy as fluid builds up. In severe cases, the leg may feel warm or appear bluish; a swollen vein may also be visible. DVT can cause fever, too.

Complications are uncommon if the clot remains in the calf; in fact, the body can often dissolve a clot in the calf without medication. Unfortunately, these clots are likely to move upward to the veins of the thigh and pelvis, setting the stage for complications. The most serious complication is pulmonary embolism. This occurs when part of the clot breaks off and travels to the lungs, where it can block blood flow and affect breathing. Pulmonary embolism is a medical emergency. It kills as many as 300,000 Americans a year. People with a pulmonary embolism may develop chest pain, shortness of breath, a cough that brings up blood-tinged sputum, low levels of oxygen in the blood, low blood pressure and an abnormal heart rhythm. They may also collapse. Most people who die of a pulmonary embolism do so within two hours of experiencing symptoms.

Another complication of DVT, called post-phlebitic syndrome, occurs when the clot puts so much pressure on the vein and its valves that the vein is permanently damaged. If the damage is severe, the valves no longer prevent the backflow of blood. Fluid then builds up in the affected leg, upping the risk of infection, skin ulcers and discoloration and chronic pain.

Because a pulmonary embolism can be life-threatening, and because people who have had one episode of DVT, especially men, are likely to have another, prevention is a top priority. If you are hospitalized, your doctors should take steps to protect you from DVT, but at home, prevention is your job. Keep moving, go for a daily walk, avoid prolonged bed rest, stay as lean as possible, don't smoke and stay well-hydrated.

Air travel poses added risks. The dry air makes blood "thicker" and "stickier," and thus more likely to clot. Cramped quarters limit movement, too. When possible, choose an exit row or an aisle seat for more leg room. Stretch, massage your lower legs, and pump your feet up and down for about 30 seconds every half-hour. Walk in the aisle hourly. If you are at high risk of DVT, consider breaking up long flights into shorter segments. Talk with your doctor about wearing elastic compression stockings; people at the highest risk should ask about preventive medication. Most people rarely think about their veins. But when you check into a hospital or take a long flight, be sure to take steps, literally and figuratively, to promote blood flow in your veins. It could save your life.