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Study simulating aircraft conditions suggests increased risk of venous thrombosis (p 1657)

November 08, 2000

Two weeks after a study published in THE LANCET concluded that there was no increased risk of venous thrombosis from air travel (Kraaijenhagen RA, Haverkamp D. Travel and risk of venous thrombosis. Lancet 2000; 356: 1492-93), a research letter published in this week’s issue of THE LANCET suggests an increased risk of venous thrombosis in a study which involved the simulation of aircraft conditions.

Aeroplane flights are thought to increase the risk of venous thrombosis, but the mechanism behind this effect is unknown. Suggested risk factors are a hypobaric (low pressure) and hypoxic (low oxygen) environment, sedentariness, and dehydration. Bj'�rn Bendz and colleagues from Ullev'ål University Hospital, Oslo, Norway, investigated whether acute exposure to reduced air pressure, similar to that encountered in aeroplane cabins, activates blood coagulation.

20 healthy men took part in the study, which was done in a hypobaric chamber, built as a comfortable modern apartment, in Sjumilskogen, Trysil, Norway. After acclimatising to the ambient air pressure, they were exposed to 76 kPa within 10 minutes; this air pressure corresponds to the atmospheric pressure at 2400 metres and is similar to the pressure in aeroplane cabins. The participants were allowed to do most everyday indoor activities except for physical exercise. After 8 hours, eight of the participants returned to air pressures at baseline level, and the remainder participated in another high-altitude experiment.��

The investigators found an increase in levels of the compounds associated with blood clotting; concentrations of prothrombin fragments 1 and 2 increased to a maximum of 2.5-fold at two hours, whereas concentrations of thrombin-antithrombin complex increased 8.2-fold.

Bjorn Bendz comments: “Despite the lack of an adequate control group at normal atmospheric pressure, our study suggests that rapid exposure to an air pressure encountered in aeroplane cabins activates coagulation. This activation is probably clinically relevant and may contribute to the increased risk of venous thrombosis. Although rare during air flights, venous thrombosis is serious and potentially fatal. Sedentariness and dehydration probably add to the risk of thrombosis and cause a hypercoagulable state. We propose that airlines give simple advice to customers on how to use the muscle-vein pump to prevent stasis, and to ensure the provision of regular non-alcoholic drinks to prevent dehydration. Individuals with a history of venous thrombosis, specific coagulation defects, or other medical risk factors are at much higher risk, and therefore medical thromboprophylaxis-eg, low-molecular-weight heparin-should be considered”.

Contact: Dr Bjorn Bendz, Haematological Research Laboratory, Ullev'ål University Hospital, N-0407 Oslo, Norway; T) +47 22 11 91 00; F) +47 22 11 91 81; E) bjorn.bendz@ioks.uio.no

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