Low pressure and low oxygen factors in DVT and long flights

Researchers say that the risk of deep vein thrombosis (DVT) during flights may not be due simply to sitting still; they say the low pressure and low oxygen environment during air travel may also contribute to the development of deep vein thrombosis in some susceptible individuals.

The low pressure and low oxygen environment on flights they say may add to the risk of thrombosis, which is increased between 2 to 4 times after air travel, especially long flights.

The exact reasons are unclear but the scientists think although immobilisation for long periods could play a part, other flight-specific factors may also contribute.

Frits Rosendaal and a team from Leiden University Medical Centre, Netherlands, measured the concentrations of markers of clotting activation in blood samples in 71 healthy volunteers (15 men and 56 women), during an 8-hour flight, 8 hours at a cinema, and 8 hours of normal activity.

Measurements were tested in blood samples before, during, and after each situation.

They found increased concentrations during the flight but not in the other two situations.

Concentrations were found to be higher in the 40 per cent of volunteers with other thrombosis risk factors - a mutation in the factor V gene and those on oral contraceptives.

Professor Rosendaal concludes that "Activation of coagulation [clotting] occurs in some individuals after an 8 hour flight, indicating an additional mechanism to immobilisation underlying air travel related thrombosis."

However other experts insist that prolonged immobilisation in a sitting position plays an important role in provoking thrombosis and this applies to trips by train or car as well.

They continue to recommend exercising during flights, wearing compression stockings, and avoiding excess alcohol and sedatives.

The research is published in the current issue of The Lancet.