Air travel has become a well-known risk factor for venous thrombosis with an absolute risk of 1 in 4600 long-haul flights and a dose-response relationship with duration and number of flights. In... Show moreAir travel has become a well-known risk factor for venous thrombosis with an absolute risk of 1 in 4600 long-haul flights and a dose-response relationship with duration and number of flights. In this thesis we studied the pathophysiology that underlies the risk as well as the effect of behaviour of passengers on the risk of thrombosis after air travel. To study the pathophysiology, we conducted a case-crossover study in which we investigated the effect on the coagulation system of 8 hours of air travel, 8 hours of immobilisation in a cinema and 8 hours of daily activities in 71 volunteers. Behaviour of passengers was studied in the MEGA study, a large case-control study on risk factors of venous thrombosis. The main conclusion of this thesis is that immobilisation alone does not explain coagulation activation after air travel. A factor that seems to contribute is hypoxia. The results of this thesis do not support the theories that fluid loss, air pollution, infection or stress play a role in coagulation activation after air travel. Certain kinds of behaviour during air travel affect the risk of venous thrombosis. Lastly, harmless prevention methods possibly counter the effect of immobilisation. Show less
In venous thrombosis, a blood clot develops in a vein, usually a deep vein of the leg, causing obstruction of the blood flow. Venous thrombosis is a multicausal disease, in which genes and... Show moreIn venous thrombosis, a blood clot develops in a vein, usually a deep vein of the leg, causing obstruction of the blood flow. Venous thrombosis is a multicausal disease, in which genes and environment interact. One of the environmental factors that increases the risk of venous thrombosis is long distance travel. This thesis describes the results of several studies on epidemiological aspects of the association between long distance travel and venous thrombosis. In a study among frequently traveling employees of international organizations, the absolute risk of venous thrombosis after long distance flights, the effect of duration of travel, time after travel and exposure to several flights at the same time and the effect of interaction with other risk factors for venous thrombosis was assessed. In a population-based case-control study, the effect of elevated levels of coagulation factors in long distance travelers was evaluated. Finally, the occurrence of venous thrombosis among commercial airline pilots was studied. The main conclusion is that the risk of venous thrombosis in healthy travellers is not high enough to promote widespread use of aggressive prophylaxis, such as anticoagulant therapy. However, in some travellers at increased risk, the risk-benefit ratio may favour the use of prophylactic measures. Show less
