Low air pressure 'raises DVT risk on flights'

LOW air pressure and reduced oxygen on flights may be linked to an increased risk of deep vein thrombosis (DVT), rather than just cramped conditions.

A study published in the Lancet found that participants who sat on a plane for eight hours showed signs of developing DVT, but those who sat in a cinema seat did not.

The experiment looked at changes in the blood of 71 people before, during and after an eight-hour flight.

The same participants were also monitored during eight hours in the cinema and eight hours in their everyday lives.

The team, from Leiden University Medical Centre in the Netherlands, found evidence of DVT developing during the eight-hour flight, but not when the volunteers spent the same time sitting in the cinema.

Researcher Professor Frits Rosendaal said this suggested that something other than just sitting for long periods was linked to the risk of developing a clot in susceptible people.

DVT is a clot which develops in a deep vein, usually in the leg, and affects about one in 2,000 people in the UK a year.

Some people face a greater danger of DVT because they are older or have other risk factors.

It has been linked to long-haul flights, giving it the name "economy class syndrome". It can prove fatal if a clot travels in the blood to the lungs.

Prof Rosendaal recruited 15 men and 15 women with no known risk factors for DVT.

The study also involved 11 women carrying the factor V gene and 15 women taking the contraceptive Pill - both known risk factors for DVT.

Another group of 15 women who were both carrying the gene and taking the Pill was included.

After the flight, 17 per cent of volunteers showed early signs of possible clotting in the blood.

But after eight hours in the cinema only 3 per cent showed the same signs, dropping to just 1per of volunteers during everyday activities.

The risks were greatest for those with both risk factors.

The study found that 43 per cent of those with the factor V gene and taking the Pill were showing early signs of possible clotting. This compared with 9 per cent of those with one risk factor and 10 per cent of those with no risk factors.

The role of the Pill as a risk factor was cited in the death of 23-year-old Katie McPherson, a student from Renfrewshire, who became a DVT victim in January 2003.

Katie's family claimed a 25-minute flight to Belfast from Glasgow a few weeks before Ms McPherson fell ill, and a change to her contraceptive Pill only ten days before her illness, could have contributed to her death.

Prof Rosendaal said: "The bottom line is that there is something happening on the plane as well as immobilisation. We only think it is the low pressure and low oxygen, but we can't be sure.

"Immobilisation is probably still the most important thing linked to the development of DVT, but something else is occurring that does not happen on the ground."

Prof Rosendaal said that increasing air pressure on planes could help, but this was difficult to achieve.

Farrol Kahn, of Aviation Health, which promotes the wellbeing of air passengers, said the study was very important.

"We have known since the 1980s that immobilisation on board planes probably does increase the risk of DVT."

Mr Kahn said that people could reduce their risk of DVT by wearing flight socks during long trips.