Sitting still for too long is likely cause for clots on flights, study says

Article By: Cynthia Ross Cravit

Don’t sit still for it – for too long on flights, that is. New study says that long periods of sitting, not low cabin pressure, is the likely cause for potentially fatal clots.

Instead the condition known as deep vein thrombosis (DVT) is more likely to arise from sitting still for long periods of time causing blood to pool in the lower extremities, according to researchers.

“The most important factor is probably, and generally thought to be, the effect of prolonged sitting with relatively little mobility,” said lead study author Dr. William Taff, a senior lecturer in cardiology at the University of Leicester in the U.K. “That really is the factor that is common to air travel and travel by road and travel by rail, all of which long journeys are associated with an increased risk of forming a blood clot.”

Blood clots that form in the leg vein become dangerous when the clot moves up the leg vein into the heart and then into the lung. Experts warn that any mode of travel - cars and trains as well as planes - and also spending hours in front of a computer could lead to the formation of a deep-vein thrombosis (DVT) in the leg.

In most cases of DVT, the clots are small and do not cause any symptoms. The body is able to gradually break down the clot and there are no long-term effects. But the larger clots may

partially or totally block the blood flow in the vein and cause symptoms such as:

• swelling of the calf which is different than mild ankle swelling that many people experience during long haul flights

• pain in the lower leg, which may intensify when you walk

• breathlessness or chest pain

The U.K. study, which was published in the Journal of the American Medical Association, included 73 healthy volunteers who spent 8 hours seated in a hypobaric chamber that was similar to the conditions of an airline cabin at about 2,400 metres (8,000 feet). Similar measurements were then taken of the same volunteers about one week later in a chamber with normal air pressure.

In each incidence, blood was drawn before and after exposure to measure factors associated with blood clotting. Blood results from each environment were then compared.

“Essentially, we found no difference between the low pressure and the normal pressure exposures,” Toff was quoted in a Canadian Press report.

The overall risk of DVT on a long-haul flight – lasting four hours or more - is estimated at one passenger in 2,000. For people with known risk factors, the risk may be slightly higher.

DVT has been previously associated with long-haul air travel, but it has been unclear whether this is due to the effects of sitting for a long time, or whether there is a relationship with some other specific factor in the airplane environment. The researchers have advised travellers to stretch their legs, extend and flex the knees and ankles, and stand and walk whenever possible during flights.

"Other preventive measures might include wearing graduated compression stockings. In people at the highest risk (e.g. a person who has previously had a flight-related thrombosis), the use of anti-coagulant drugs, such as low-molecular weight heparin, might be considered," Toff said.

Other risk factors for deep vein thrombosis (DVT) include:

-- Increasing age

-- Previous blood clots or venous thrombosis

-- Family history of venous thrombosis

-- Suffering from or having had treatment for cancer

-- Certain blood diseases

-- Being treated for heart failure and circulation problems

-- Recent surgery especially on the hips or knees

DVT is also more common in women who:

-- Are pregnant -- Have recently had a baby -- Are taking the contraceptive pill

-- Are on hormone replacement therapy or HRT.

Combinations of risk factors may be synergistic - that is to say, the combined risk is more than additive.

Dr Toff concluded: "Long-haul travel, whether by air or other modes, is associated with an increased risk of thrombosis and travellers should consider taking appropriate steps to minimise that risk."