Previous studies have found a 2-4-fold increased risk of thrombosis after air travel; with a greater risk after longer flights than after shorter ones. The mechanism of clot formation during air travel, however, is unclear. Scientists think immobilisation for long periods could play a part, but flight-specific factors may also contribute.
To investigate, Frits Rosendaal (Leiden University Medical Centre, Netherlands) and colleagues measured the concentrations of markers of clotting activation in blood samples from 71 healthy volunteers before, during, and immediately after an 8-hour flight. To disentangle specific flight factors from immobilisation alone, they compared the concentrations in the same individuals at the same time points during 8 hours of sitting in a cinema and 8 hours of regular daily activities. 40% of the participants also had an increased risk of thrombosis, by being carriers of a mutation in the factor V gene or taking oral contraceptives. The authors found increased concentrations in markers during flight compared to the other two situations, especially in volunteers with other risk factors for thrombosis.
Professor Rosendaal concludes: "Activation of coagulation [clotting] occurs in some individuals after an 8-h flight, indicating an additional mechanism to immobilisation underlying air travel related thrombosis."
See also accompanying Comment by Hans Stricker (Ospedale Regionale, Locarno, Switzerland).
Contact: Professor Frits R Rosendaal, Department of Clinical Epidemiology Leiden University Hospital, Leiden University Medical Centre, PO Box 9600, 2300 RC. T) +31 71 526 4037 f.r.rosendaal@lumc.nl
Comment: Dr Hans Stricker, Ospedale Regionale, Via all'Ospedale, CH 6600 Locarno, Switzerland. T) 0041 91 811 45 49 hans.stricker@eoc.ch
The Lancet