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Friday, 10 November, 2000, 00:49 GMT
More evidence of flying risk
airline seats
Cramped airline seats are blamed for thrombosis
Tests on volunteers exposed to the same conditions as air passengers may help explain why some get dangerous blood clots.

The experiments, described in The Lancet medical journal, suggest the sudden change in air pressure experienced within the cabin may be partly to blame.

We want every person who books a flight to be sent some low dose aspirin by the travel agent along with their ticket

Farrol Kahn, Aviation Health Institute
Earlier studies suggest a significant number of cases of deep vein thrombosis, in which unwanted clots form in veins, often in the legs, are caused by long-haul airline travel.

These clots can be potentially fatal if they break away from their original location and travel to the the lungs, blocking vital blood vessels.

Researchers from Oslo in Norway put 20 healthy male volunteers in a "hypobaric chamber", built to seem like a perfectly ordinary apartment.

Within this, the air pressure was manipulated over a 10 minute period to simulate the pressure normally encountered within aircraft cabins.

This was maintained for eight hours, at which time the volunteers were "brought back to earth".

All the volunteers showed pronounced physical changes during that period.

Not only did the oxygen saturation in their blood fall away, but the concentrations of body chemicals associated with blood clotting increased.

When the body is not getting enough oxygen, its natural reaction is to compensate by producing more red cells in the blood to carry as much oxygen as possible.

This higher concentration of the cells makes the blood thicker, and more liable to clot.

The researchers wrote: "Despite the lack of an adequate control group at normal atmospheric pressure, our study suggests that rapid exposure to an air pressure encountered in aeroplane cabins activates coagulation."

This, they say, could well contribute to the risk of dangerous clots forming.

Interestingly, none of the volunteers were subjected to the other conditions associated with air travel which experts say may increase the risk of deep vein thrombosis.

Air pressure

The recycled air used in aircraft cabins contains less oxygen than normal air, in addition to the reduced pressure - this also might tend to encourage blood thickening.

Airline passengers are also breathing far drier air than the moisture rich variety at ground level. This contributes to dehydration, particularly if alcohol rather than water is being drunk, and thickens the blood still further.

Finally, passengers - particularly those in economy class - have less room than normal to move around and boost circulation to their lower limbs, increasing the risk still further.

Farrol Kahn, head of the Aviation Health Institute in the UK said the research represented more evidence that deep vein thrombosis was a real risk associated with airline travel.

He said: "We want every person who books a flight to be sent some low dose aspirin by the travel agent along with their ticket.

"People who can't take this, such as pregnant women, should get a compression stocking for their legs which should improve circulation."

He added: "The airlines don't want to circulate 100% fresh air in the cabins on the grounds of cost, but I'm sure passengers would not mind paying more for it."

The Stroke Association said it was important for people to get up and move around on a regular basis during a flight.

A spokeswoman said: "This gives the blood a chance to flow around the body.

"When blood slows down it may form a clot in the legs."

The charity also advises people to drink lots of water as this helps prevent the body from becoming dehydrated.

Some may want to take an aspirin before flying because it is known that aspirin helps to reduce the stickiness of the blood cells, the charity says.

However, those with high blood pressure or other medical conditions should talk to the pharmacist or their GP about this first.

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See also:

27 Oct 00 | Health
Blood clot travel link disputed
13 Apr 00 | Health
Aspirin cuts blood clot danger
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