DVT—The Silent Killer


Not long ago, had you seen an article entitled “DVT” you probably would not have opened it or had any idea what it was about.  What a difference a few months makes.  After some highly publicized disasters in late 2000, it is now a hot topic.

Deep  venous thrombosis first appeared on the medical scene during World War II among Londoners who sat for hours on end in air-raid shelters. Years later, the diagnosis began to pop up among airline travelers on long flights.

Background—signs & symptoms

DVT is a medical condition where blood clots form in the veins of the legs or pelvis, sometimes causing discomfort and swelling. But clots can be present with no apparent symptoms. Untreated, they can break off and travel to the heart or lungs, often causing chest pain and shortness of breath.  They are often fatal.

After the highly publicized cases last year, doctors, researchers and airline industry experts are beginning to take a deeper look into the relationship between flying and DVT.  It is popularly known as "economy class syndrome," but that term is misleading.  DVT is not limited to those who sit in cramped airline. The condition can occur in any people who sit for long periods--in buses, trains, cars, theaters or at their desks.

DVT begins with the pooling of blood in the deep leg veins. During a period of only a few hours, if the legs are not exercised, blood clots can form. As the clots grow, they tend to shed pieces (emboli) that are carried through the bloodstream to the heart. From there, they go out into the lungs. This process is known as embolization.


In spite of all the publicity, there is no evidence that the incidence of DVT is rising.  There may be more actual cases occurring, but this is likely just because more people are flying, taking long car trips or have sedentary jobs.

For a number of years now there have been about 2000 people per year known to die from this syndrome.  It is more common in women who are pregnant or on birth control pills, or in people who are sick and dehydrated. It is also much more common after long flights -- trans-Pacific versus trans-Atlantic, which is why you hear more about it on flights to Australia.

According to one study, the estimated incidence of DVT in the lower extremity is one per 1,000 persons per year. Other experts believe the figure may be higher. In the U.S. there are as many as 600,000 persons with this condition hospitalized each year.

Predisposing factors

Anyone who stays in one position for a long time may develop small clumps of clotted blood in the legs or pelvis. Stagnation of fluid in the lower limbs while seated is a relatively common occurrence. A frequent symptom is swollen feet and ankles. If the stagnation lasts long enough, small blood clots may form.  These clots usually dissolve before they can do any harm.  But they can grow into large clots and then break off and go to the heart and lungs.  A clot in a major vein can measure several inches. If a relatively big embolus were to reach the heart and lungs, death could result.

People who have an embolus often experience severe chest pain and shortness of breath. They will often seek a physician, concerned about a possible heart attack. Because these symptoms may occur several days after a flight, an association between the flight and the symptoms may not be noticed.

Some people are especially at risk. These include women over 40 years old or on birth control pills, those with a history of DVT or varicose veins, tall people, obese people, cancer patients, people who have had a recent surgery or major injury, people with a strong family history of DVT, and others on certain medications like diuretics.  Smokers are also at increased risk.

Air travel factors

The link between DVT and flying continues to be hotly debated. Medical studies have produced conflicting evidence so far, with researchers clashing over the importance of such factors as mobility, pitch (or the space between seats), dehydration and cabin air pressure.

Two studies, reported last year in Lancet, concluded that extended travel - by air, car, bus train or boat -does not raise the risk of DVT.  But another study showed that as many as 10% of passengers on long haul flights developed clots in their legs.  This was sufficient for the British House of Lords' Science and Technology Committee to recommend that "airlines and their associates reappraise their current practices in relation to not only the provision of information for passengers but also the design of the cabin and cabin service procedures.”

Some experts are focusing their attention on aircraft seats. Stanley Mohler, aerospace medicine specialist at Wright State University, points out that the airline seat was primarily designed to meet crash standards rather than the health concerns. They were designed for a 170-pound, 5-foot-7-inch individual, which Mohler reminds us is no longer realistic.  Taller and heavier passengers often can't budge once they have sat down. The same is true for most people sitting in economy class and by the window or in the middle seat.  With the increased inconvenience of getting out, one is more inclined to sit still. Seat pitch in economy class now generally runs 28-31 inches. Mohler recommends that seat pitch should be 40 inches. But most airlines balk at the idea of expanding economy-class legroom, arguing that such a measure would force them to increase fares.


Deciding whether to reconfigure airplane seating, however, is not the only answer.

Airlines around the world are stepping up their warnings, both oral and written - and highlighting some of the latest measures they have been undertaking to promote healthy flying. Air Canada and Japan Airlines both offer in-flight videos on exercises passengers can do in their seats.

The lawsuits and negative publicity they have been getting may well alert airlines to the fact that "passenger safety" consists of more than just getting them to their destination without external injury.  If airlines need to be held in any way responsible, perhaps it is only if they make a habit of keeping the 'Fasten Seat Belt' light on for the convenience of the crew rather than for actual passenger safety. It is a fact, though, that only the captain knows when the risk from turbulence outweighs the risk from DVT.  But perhaps rather than selling duty-free items, the flight attendants could lead the passengers in a round of calisthenics!

Passengers should drink plenty of fluids. Smoking, which damages the blood vessels, should be avoided. So should alcohol and caffeine, which tend to be dehydrating. Sitting in an aisle seat is helpful, because it provides greater legroom than an inside seat. Passengers should avoid crossing their legs; they should shift the position of their bodies in their seats from time to time and, when possible, walk in the aircraft aisles; moving blood is less likely to clot.

Passengers can also exercise in their seats. One exercise suggested by British Airways is to bend the feet upward, spread the toes and hold for three seconds; then point the feet down, clench the toes and hold for three seconds.

Whether aspirin helps is debatable. It does, indeed, help to prevent the clumping of platelets, one of the steps in forming blood clots.  But it has not shown much promise in other (non-travel related) studies of DVT.  For those who tolerate aspirin, a half tablet taken two days prior to flight and another on the day of flight may at least be harmless.

Clothing makes a difference.  Loose-fitting clothes are an advantage. Girdles or stockings with tight, below-the-knee elastic bands should be avoided. On the other hand, elastic stockings reaching all the way up the thigh have been recommended as a preventive measure. 

Added to this is the simple matter of lifestyle. An active lifestyle, filled with regular exercise and maintaining a lean, physically fit body helps prevent DVT.

To summarize, here are some steps you can take to avoid DVT when flying:

  • For more legroom, book an exit row or aisle seat, if possible.
  • Drink lots of fluids - but not alcohol or caffeine.
  • Keep your legs moving - walk around, stretch your legs every hour or two.
  • Massage your feet, ankles, legs and knees to keep blood circulation going.
  • While seated, do simple exercises such as clenching your toes or pulling your knees up.
  • If you have had blood clots in the past, ask your doctor about wearing elastic stockings.
  • Wear loose-fitting clothes and shoes
  • If your doctor agrees, take one Aspirin tablet each day for three days leading up to your flight.

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