Medical researchers in the Netherlands have found that lack of oxygen and pressure are also factors in the development of deep vein thrombosis (DVT) during air travel, rather than simple immobility, in a study that could affect airlines' future cabin configuation choices.
While immobility has been cited as a potential factor in the onset of DVT the Dutch study aimed to discover whether other elements, specific to air transport, might also play a role – notably hypobaric hypoxia, the depletion of oxygen supply to body tissue resulting from reduced air pressure in aircraft cabins.
Pressure has previously been cited as a potential factor behind DVT but previous studies in this area have generated conflicting results. The latest research has tried to eliminate possible distortion by taking into account such factors as passenger immobilisation and the effects of circadian rhythm.
Researchers subjected 71 volunteers to a long-haul flight of 8h and, for comparison, exposed them to an 8h period in a cinema as well as regular daily activities.
“Results from [earlier] studies suggest a two- to four-fold increased risk of thrombosis after air travel, with a greater risk after longer flights than after shorter ones,” says the study, conducted by Amsterdam’s academic medical centre and Leiden University, and published in the latest edition of medical journal The Lancet.
“The mechanism of thrombus formation during air travel, however, is unclear. Immobilisation for long periods could play a part as could flight-specific factors – for example, hypobaric hypoxia, which might activate the clotting system.”
Flight tests took place in May 2004 on board a chartered Boeing 757 out of Amsterdam, during which the participants were instructed to stay seated as much as possible. The aircraft cruised at 36,000-39,400ft (10,900-11,940m) and was pressurised to a cabin altitude of 5,900-6,900ft.
Similar restrictions on movement were imposed on the volunteers – comprising 56 women and 15 men aged 20-39 years – during the cinema screening two weeks later.
The study examined three types of blood coagulation marker and one of these markers, the concentration of thrombin-antithrombin complex, showed a strong increase in several individuals following the flight but decreased during the cinema and daily-life control situations.
“Our findings indicate that flight-associated factors…lead to increased thrombin generation after air travel,” concludes the study. It adds that particular individuals, such as those with hereditary coagulation disorders and those taking oral contraceptives, appear to be at higher risk.
While the study does not formally link cabin pressure to the onset of DVT, it is sceptical that other air travel-related effects, such as dehydration or anxiety among passengers, would have led the results observed.
DAVID KAMINSKI-MORROW / LONDON
Source: Flight International
