title: Explanations for coagulation activation after air travel.
abstract: BACKGROUND
  It is unknown whether venous thrombosis after long haul air travel is exclusively attributable to immobilization.
  
  
  OBJECTIVE
  We determined whether the following mechanisms were involved: hypoxia, stress, inflammation or viral infection.
  
  
  METHODS
  In a case crossover setting in 71 healthy volunteers who were exposed to an 8-h flight, 8-h movie marathon and 8 h of regular activities, we compared markers for several hypothetical pathways: plasminogen activator inhibitor-1 (PAI-1), stress, plasma factor (F)VIII coagulant activity (FVIIIc), soluble P-selectine (sP-selectine), interleukin-8 (IL-8) and neutrophil elastase. We reported earlier an activated clotting system, as evidenced by thrombin generation, in 17% of volunteers after the flight.
  
  
  RESULTS
  PAI-1 increased by 4.2 ng mL(-1) (CI95:-49.5 to 6.5) in volunteers with an activated clotting system whereas it decreased in those without (-20.0 ng mL(-1), CI95:-33.2 to -14.0). FVIIIc levels rose more in individuals with clotting activation (18.0%, CI95:-1.0 to 33.0) than in those without (2.0%, CI95:-2.0 to 5.0). The increases in FVIIIc were not associated with stress, which appeared unrelated to clotting activation. sP-selectin increased in those with clotting activation (3.5 microg L(-1), CI95: -3.0 to 10.0), but decreased in those without (-0.5 microg L(-1), CI95: -2.0 to 2.0). Changes in levels of neutrophil elastase or IL-8 were not different between the subjects with and without clotting activation.
  
  
  CONCLUSIONS
  Our results do not support the hypotheses that stress, infection or air pollution are involved in the development of a prothrombotic state in air travellers. After long haul air travel, this state is more pronounced in patients with risk factors and may be caused by hypoxia, triggering systemic inflammation and platelet activation, leading to coagulation induction and degranulation of platelets.
authors.affiliation: Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: A J M
authors.initials: AJ
authors.lastname: Schreijer
authors.forename: M F
authors.initials: MF
authors.lastname: Hoylaerts
authors.forename: J C M
authors.initials: JC
authors.lastname: Meijers
authors.forename: H R
authors.initials: HR
authors.lastname: Lijnen
authors.forename: S
authors.initials: S
authors.lastname: Middeldorp
authors.forename: H R
authors.initials: HR
authors.lastname: Büller
authors.forename: P H
authors.initials: PH
authors.lastname: Reitsma
authors.forename: F R
authors.initials: FR
authors.lastname: Rosendaal
authors.forename: S C
authors.initials: SC
authors.lastname: Cannegieter
mesh_terms: D001359:Aviation; D001777:Blood Coagulation; D001779:Blood Coagulation Factors / Q000378:metabolism; D018592:Cross-Over Studies; D006801:Humans; D014195:Travel; D020246:Venous Thrombosis / Q000097:blood
chemical_list: D001779:Blood Coagulation Factors