15 February 1999

Travel For Clots

Travelers who sit in excess of five hours on planes, in automobiles, and on trains are at "relatively high risk" of getting post-travel blood clots in their legs, according to the first case-controlled study of seat-bound passengers, published in the February issue of CHEST.

In an article in the journal of the American College of Chest Physicians (ACCP), Emile Ferrari, cardiologist at the Hospital Pasteur, France, along with three colleagues, reported results from a study of 160 consecutive cases of deep vein thrombosis (blood clots) which were treated over a three-year period. Almost 25 per cent of the patients (39 cases) had recently completed a journey lasting longer than five hours. The vast majority, 28, traveled by car, while nine traveled by plane, and two by train. Dr. Ferarri noted that the study illustrated that all forms of travel could be associated with blood clots, not just air travel.

Blood clots in the arteries, called deep vein thrombi, can cause pain and swelling in the legs. Sometimes, they dislodge and move to the lungs, resulting in a deadly pulmonary embolism.

According to the researchers, the odds of having blood clots in the legs as a result of extended seated travel was almost four times higher in the study group, as compared to the 160-person control group which was hospitalized for other cardiac problems such as chest pain.

In the study, Dr. Ferrari points out that the incidence of post-travel blood clots was relatively high compared to previous retrospective reports of 3 to 17 per cent in the literature from cases for which there was no confirming detail.

The researcher said that passenger apathy and inertia increased the risk of clots by reducing both muscle activity and blood flow in the veins. Also, dehydration and diminished urine output associated with high altitude cabin pressure can lead to lower fluid content in the blood plasma , setting off complex reactions that cause coagulation.

To avoid "memory bias," the investigators asked study participants and the control group 300 questions twice, at their bedside shortly after admission and just before discharge. Included were 12 questions on travel. Patients with limited mobility and those receiving anticoagulant or antiplatelet therapies were excluded from participation.

Dr. Ferrari said that few, if any, patients showed clinical signs of deep vein thrombosis prior to hospitalization following travel.

Dr. Ferrari believes that the cases diagnosed in this study represent only the tip of the iceberg of all cases occurring after travel. The bulk of deep vein thrombosis cases caused by travel, he said, remains undiagnosed.

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