According to new research from the UK the reduced air pressure and oxygen levels experienced by travellers on long flights are not responsible for the formation of deadly blood clots often referred to as "economy class syndrome".
Deep vein thrombosis (DVT) after long-haul air travel was first reported more than 50 years ago but it remains unclear whether this is due to the effects of prolonged sitting, as in other modes of travel, or whether there is a relationship to some other specific factor in the airplane environment.
One commonly assumed factor, which has attracted attention, is hypoxia, a deprivation of oxygen, associated with decreased cabin pressure and there has been some experimental evidence from studies to support the theory.
Researchers from Leicester University say their research has found that cabin pressure and oxygen changes are not the culprits when it comes to DVT and air travel.
The findings support the theory that clots develop in otherwise healthy people mainly because they are sitting in cramped quarters for extended periods and blood flow, especially in the legs, is restricted and the actual cabin environment is not a factor.
For years now travelers have been advised to attempt to exercise their leg and calf muscles or walk around the cabin in order to prevent the development of potentially deadly clots that can travel to the lungs, brain or heart.
It seems the same problem is likely to occur during long car or train trips.
For their research the UK team, between September 2003 to November 2005, tested 73 healthy volunteers recruited by local advertisement and assigned them to 1 of 3 groups.
One group were between age 18 and 40 years with no known risk factors for venous thromboembolism.
A second group was made up of women between the ages of 18 and 40 years who were taking a combined oral contraceptive pill.
A third group was made up of individuals aged 50 years or older.
Excluded from the study were those with a history of venous thromboembolism, or a close relative with the condition or those who had taken an anticoagulant or antiplatelet medication in the 2 weeks before the study.
All were screened for factor V Leiden G1691A and prothrombin G20210A mutation ( risk factors for thrombosis) and excluded if they tested positive.
Air travel was not permitted within 1 week before each exposure.
The volunteers were allowed to drink nonalcoholic beverages and were given a light midday meal and snacks and were asked to report any symptoms or signs of venous thromboembolism during or within a week after each test.
The same group were then retested a week later at ground-level pressure and oxygen levels and blood samples were taken before and after each of the tests.
The researchers found no significant difference between the two tests on clot formation, on the breakdown of small, naturally occurring clots, in the activation of platelets, cells in the blood that clump together when stimulated to promote clot formation, or in the action of endothelial cells that line the interior surface of blood vessels.
Although the problem has been termed "economy-class syndrome", the American Heart Association says victims have been reported throughout cabin classes for years.
The association advises air travelers to drink extra water, walk if possible during the flight and avoid alcohol.
The team concluded that their findings do not support the hypothesis that the atmospheric conditions that might be encountered during long-haul air travel, is linked to an increased risk of deep venous thrombosis.
The study is published in the current edition of the Journal of the American Medical Association.