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Sitting in Cramped Position, Not Hypoxia or Low Humidity, Increases Risk of Blood Clots: Presented at ISTM

By Charlene Laino

New York, NY -- May 9, 2003 -- The first research using real travel conditions to analyse the mechanism of travelers' thrombosis has found that sitting in a cramped position for long periods -- whether in an airplane or a bus -- can activate the blood's coagulation system, leading to an increased risk of venous thromboembolism.

Wolfgang Schobersberger, MD, a professor of intensive care medicine at the University of Innsbruck, in Austria, presented the findings here on May 8^th at the 8^th Conference of the International Society of Travel Medicine.

Several years ago, researchers linked long-haul flights to an increased risk of deep vein thrombosis (DVT), blaming the events on high altitude, low humidity and low oxygen pressure, Dr. Schobersberger said. But since thromboembolic events have also been reported after car, bus and train travel, his research team postulated that some other factor must be the culprit.

The prospective study enrolled 40 people at low or medium risk for DVT. Twenty flew from Vienna to Washington, D.C., and back 2 days later; the other 20 traveled by bus from Innsbruck to Rome and back 2 days later. Each trip takes about 10 hours.

Molecular markers for coagulation and fibrinolysis were measured before the trip, 5 to 8 hours into the trip, immediately after the trip, 1 day later and 3 days later.

Activated thromboelastography revealed activation of coagulation in all participants, during and after travel, regardless of whether they traveled by plane or bus, Dr. Schobersberger reported. The levels stayed elevated for at least 24 to 48 hours after the trip ended, he added.

Also, fibrinolysis was suppressed in all travelers, he said. None of the travelers developed DVT, "but we didn't expect it, with only 20 people in each group," Dr. Schobersberger said.

"Since both forms of travel increased risk, we can conclude that reduced humidity and moderate hypoxia do not play a critical role in thromboembolic formation," he said. "But sitting in a cramped position is a trigger."

Bo Eklof, MD, a clinical professor of surgery at John A. Burns Medical School, University of Hawaii, in Honolulu, said that all travelers should drink plenty of non-alcoholic fluids to avoid dehydration and frequently move their legs to reduce their risk of developing DVT during a lengthy trip.

Those at moderate risk should also wear compression stockings, sometimes called support panty hose, Dr. Eklof said. And those at high risk should have an injection of a low molecular weight heparin -- which will provide protection for about 12 hours -- immediately before the trip, he said.

Risk factors for DVT include age 60 or older, heart disease, family history of DVT, varicose veins or chronic venous insufficiency, obesity, pregnancy, malignancy and recent surgery.

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