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November 15, 2006

Air Travel, Hypobaric Hypoxia, and Prothrombotic Changes—Reply

Author Affiliations

Letters Section Editor: Robert M. Golub, MD, Senior Editor.

JAMA. 2006;296(19):2313-2315. doi:10.1001/jama.296.19.2314

In Reply: Dr Schobersberger and colleagues correctly draw attention to some of the differences between the conditions in our study and those of a long-haul flight. The aim of our study was to assess the effect on hemostatic parameters of hypobaric hypoxia, equivalent to that which might be experienced on a long-haul flight, after controlling for any effects due to prolonged sitting or circadian variation. We did not attempt to replicate all of the conditions of a long-haul flight and the absence of any apparent effect of hypobaric hypoxia on hemostasis should not be taken to imply that air travel is without risk of venous thrombosis. Data from a recent large case-control study1 indicate that long-haul air travel, with a flight duration in excess of 4 hours, is associated with a 2-fold increase in the risk of deep vein thrombosis or pulmonary embolism. The overall risk is similar during travel by other modes (eg, road or rail), suggesting that prolonged seated immobility is the most likely causative factor.1

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