In June the World Health Organization (WHO) coupled flying and other forms of travel with the risk of a potentially fatal condition, venous thromboembolism (VTE). The first phase of its study concludes that the risk is small, but increases if people are immobile for long periods in cramped conditions. The United Nations agency recommends passengers exercise their legs during long flights to reduce the risk. The value of the advice is questionable. Plane cabins are fitted out with a view to economics, not ergonomics, and sardine conditions make exercise difficult.
WHO’s Research Into Global Hazards of Travel (WRIGHT) project indicates that the risk of developing VTE approximately doubles after travel lasting four hours or more. The flying public can take some comfort in other parts of the findings. Even with this increased risk, the absolute risk of developing VTE, if seated and immobile for more than four hours, was found to be relatively low at about 1 in 6000.
The two most common manifestations of VTE are deep vein thrombosis and pulmonary embolism. In the first a blood clot develops in a deep vein – usually in the lower leg. It can be life-threatening when associated with thromboembolism. This life-threatening development occurs if the clot breaks off and travels through the body to the lungs and blocks blood flow. This is known as pulmonary embolism.
WHO said that while the danger of blood clots is the same whether people travel long-distance by train, car or plane, those in high-risk groups were more likely to develop clots on flights.
Shanthi Mendis, a DVT expert quoted in an Associated Press story about the WHO report, said other factors increase the risk. She listed obesity, genetic predisposition, age, use of oral contraceptives and being shorter than 5-foot-4 or taller than 6-foot-4. The theory is that short people are less mobile because their feet dangle and taller people because they are more cramped.
DVT usually in the lower leg, has been connected to long-distance travel since the 1950s. For years it was blamed on the reduced air pressure and oxygen levels in plane cabins, a theory that led to several highly publicized incidents and contributed to a landmark lawsuit against the airlines. A 2006 study, however, concluded that reduced air pressure and oxygen levels on planes do not increase a passenger’s risk of DVT. The report supported what airlines had been saying for years: deep vein thrombosis (DVT) is not their fault. The courts agree – for the present.
Airlines commonly warn passengers that if they have conditions that predispose them to DVT, they should talk to their physician before flying. Some also encourage periodic walking around the cabin and seated exercises. The trouble is, conditions on most flights make mobility impractical. The WHO report could mean airlines are back in the cross hairs of DVT victims in the courts.
Sources: WHO; Associated Press