STORY BYLong-distance travelers and others who are immobile for hours at a time take the risk of developing deep vein thrombosis (DVT).
Although it has long been suspected that sitting for hours contributes to DVT, until recently there has not been enough scientific research to prove the risk. DVT is not new; the condition was first described in people sitting on deck chairs in air raid shelters in London during World War II.
DVT is a blood clot that develops in a deep vein, usually in the leg or calf, when the blood begins to pool after four to six hours of inactivity in a bent leg position, such as sitting. Flying adds a unique set of circumstances.
While flying, low cabin pressure and high altitude impede the body in delivering optimal levels of oxygen to the body's tissues, explains Charles D. Ericsson, M.D., professor and clinical director of Infectious Diseases at The University of Texas Medical School at Houston. “Flying in a modern jetliner is like being at 5 to 8,000 feet above sea level.”
Also, low humidity in the plane causes a passenger to become dehydrated. This is made worse if a person has an alcoholic drink, which acts as a diuretic and promotes fluid loss, says Ericsson, who also is director of the UT Travel Medicine Clinic.
Besides staying hydrated by upping your non-alcoholic fluids, Ericsson stresses isometric exercises – flexing leg and foot muscles which will pump the blood. If you have fallen asleep for an hour or more, it is time to walk around the cabin if you can. If that's not possible, continue flexing feet and calf muscles in your chair several times per hour while you are awake.
Graduated pressure or isotonic stockings are a necessary item for long flights or car trips, as they keep the blood from pooling. They come up only to the calf.
“The socks feel really tight, especially the first time you wear them. At the end of a long journey, I am so glad to get them off, but my feet are not swollen and feel good,” Ericsson says.
The benefits of the stocking were the focus of a randomized trial. Researchers studied men and women on flights of more than eight hours. Ultrasound was used to assess deep veins before and after flight.
“As many as 10 percent of those who did not wear the stockings had asymptomatic clotting which they did not have before they got on the plane. None of the passengers who wore class-1 compression stockings developed DVT,” Ericsson says.
Up to two million Americans develop DVT each year, according to the American Heart Association.
“After a long flight, if a person has swelling in a leg as well as pain, he or she should seek medical attention. There could be other complications, and the patient may need anticoagulants,” he says, and aspirin does not count.
“Aspirin as an anticoagulant does not work in this case,” Ericsson explains. “Aspirin is useful in the arterial side of circulation but not in the veins as the blood is returning to the heart.”
The most common treatment for DVT is anticoagulant (blood thinner) medications like heparin and warfarin, which reduce the blood's tendency to clot. Patients usually do not need to stay on anticoagulants beyond the treatment period.
Those who are most susceptible to developing DVT are passengers over age 40 because risk increases with age. DVT is more common in women than men. External risk factors include smoking, obesity, decreased oxygen, oral contraceptives or hormonal replacement.
A potentially lethal complication of DVT is a pulmonary embolism (PE),which can be fatal if a clot reaches the lungs or the heart. If it reaches the brain, the result is a stroke. An estimated 200,000 people die of PE each year in the U.S., more than AIDS and breast cancer combined. These dangerous clots can be caused by a variety of risk factors and triggered by increasing age, obesity, cancer or decreased blood flow resulting from restricted mobility following major surgery such as joint replacements.
“We have learned a lot about DVT from observing immobilized post-surgery patients in hospitals, as they also are at risk,” Ericsson says.
A major contributing factor is stasis or stagnant blood in the veins. Prolonged bed rest or immobility promotes stasis. Coagulation is encouraged by the presence of tissue debris, collagen or fat in the veins. Damage to the vein walls can occur during surgery and could eventually promote clotting.
Prevention in hospitals includes movement and rehabilitation beginning the first day after surgery, along with anticoagulant therapy. Patient's legs are also placed in graded compression elastic stockings and an external compression device.
Sitting at your desk in front of the computer for too long also may put you at risk for DVT. The European Respiratory Journal reports the case of a young man from New Zealand who nearly died after developing a DVT following long periods of physical inactivity in front of his computer. A massive clot that formed in his leg broke off and traveled to his lungs.
This man was the first recorded victim of a condition called e-thrombosis. He spent up to 18 hours a day at his computer.
The same basic prevention in the car or the plane applies at your work station: get up every 30 minutes and walk.
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Dr. Charles D. Ericsson is professor and clinical director of infectious diseases at the UT Medical School.
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