Air travel and venous thrombosis. Results of the WRIGHT study. Part II: Mechanism

Abstract

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 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.