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Study Indicates Healthy Air Travelers Not at Increased Risk for DVT

A recent collaborative study conducted at two universities in the United Kingdom (UK) has called into question the link between deep vein thrombosis (DVT) and air travel. By simulating the conditions similar to those found on an eight-hour flight, researchers at the University of Leicester and the University of Aberdeen were attempting to seek proof that reduced cabin pressure and oxygen levels increase the risk of DVT.

DVT occurs when a clot forms deep in the veins, usually in the lower extremities (legs, thighs or hip area), and is often associated with pain and swelling. In addition to the discomfort, a clot could potentially either partially or completely break free, travel through the bloodstream and lodge in the lungs, causing a pulmonary embolism (PE). PE is a very serious DVT-related complication that can result in permanent damage to the lungs and sometimes death. It has been commonly asserted that flying for extended periods is a DVT risk factor due to prolonged immobility and decreased air pressure.

The study was conducted from September 2003 to November 2005. Investigators recruited 73 healthy volunteers, screening them for inherited forms of thrombophilia, such as Factor V Leiden. In order to recreate the conditions one might find in an aircraft cabin, volunteers sat in a hypobaric (reduced air pressure) chamber for eight hours. They only moved around for a few minutes each hour. A week later, the same volunteers were placed in a controlled environment, again spending eight hours in a seated position but in ground-level (normobaric) atmospheric conditions. Blood was drawn from each volunteer before and after exposure in order to measure clotting. Results showed no significant difference between clotting levels for the hypobaric and normobaric exposures.        

William D. Toff, MD, is from the University of Leicester's Department of Cardiovascular Sciences and one of the main investigators. "Our study provides, for the first time, a carefully controlled assessment of the effects on blood clotting of the low air pressure and low oxygen level that might be found during a long-haul flight. We found no evidence that these conditions cause activation of the blood clotting mechanism," said Toff.

While study findings suggest that healthy, commercial flight passengers are not at increased risk when traveling, those in other risk categories for DVT should continue to take precautions. Designated risk categories include inherited thrombophilia, pregnancy, cancer, immobilization, obesity, and the use of medications such as birth control pills and hormone replacement therapy.

Overall, a reasonable and informed approach is recommended. "People undertaking long-haul travel should take sensible precautions appropriate to their own inherent level of risk. For everyone, that should include regular leg exercises and getting up to walk around from time to time when conveniently possible. People with known risk factors should take advice about other preventive measures, as described, for example, on the Department of Health website," added Toff.

The study was funded by the UK Department for Transport, the UK Department of Health and the European Commission. The study report, "Effect of Hypobaric Hypoxia, Simulating Conditions During Long-Haul Air Travel, on Coagulation, Fibrinolysis, Platelet Function, and Endothelial Activation," appears in the May 17, 2006 issue of The Journal of the American Medical Association.  

Source: BBC News, May 16, 2006 and Medical News Today, May 17, 2006


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