HOSPITAL consultant Patrick Kesteven is no stranger to long-haul flights. As an Australian, now working at Newcastle's Freeman Hospital, he has spent many hours at 30,000 feet crossing from one side of the planet to the other.

He admits that he never used to worry about the phenomenon known as DVT (Deep Vein Thrombosis), but after a string of high-profile deaths involving long-haul airline passengers, he does now.

"I got stuck on the tarmac at Amtsterdam airport last Friday when all the computers went down and I made sure I kept wiggling my legs," says Dr Kesteven. "It really does seem to be becoming more frequent. It may be partly due to greater awareness of DVT but there is no doubt that more people are now travelling longer distances," says Dr Kesteven, a consultant haematologist who is heavily involved in what is expected to be the largest ever scientific study of DVT on behalf of the World Health Organisation.

"Long haul flights these days can be extremely long and relatively cheap and everybody seems to be popping off to Australia or South Korea," he says.

While our knowledge of what causes DVT is incomplete, there seem to be some broad hints which travellers should follow. It seems the days of flopping out on a long-haul flight and drinking yourself silly are over - or at least they should be.

Sitting still for a long time and alcohol are two factors associated with Deep Vein Thrombosis (DVT) which has been linked to the deaths of several passengers in recent years. Concerns about the condition were highlighted when bride-to-be Emma Christoffersen, 28, from Newport, South Wales, died of a blood clot after sitting for 20 hours during a flight from Australia to Britain in October 2000. The case sent shockwaves through the airline industry after a post-mortem examination revealed Deep Vein Thrombosis killed her. More recently, 28-year-old Alayne Wake, from Sunderland, died of a blood clot last December while travelling back from Singapore, despite the frantic efforts of air crew to save her life.

Travelling in first or business class which allows more leg room than economy does not necessarily remove the risk of DVTs which are blood clots in the deep veins of the legs. A first class passenger died recently, the day after getting off a six-and-a-half hour flight from Miami to Gatwick.

Ann Price, 57, of Bottesford, Nottingham, died from a blood clot which travelled to her lungs and her family believe it was triggered by the flight. Her daughter, Jacqui Dixon, says: ''It is wrong to call this Economy Class Syndrome. The airlines should give a lot more advice to passengers on what to do."

Where you sit, how long you fly for or indeed if you fly at all is not necessarily related to whether you form a blood clot or not. That's because DVTs seem more likely to form during long periods of inactivity, which may also occur on coaches or trains, for example. Normal leg movement usually allows calf muscles to pump blood around the body, but when legs are still, the blood pools and gets sticky, making it more prone to clot in the calf.

It is not yet known whether low air pressure and oxygen on flights help clots to form but, as part of the WHO investigation, volunteers will be strapped in to a mock-up of an airliner at Farnborough, Hamphshire and subjected to different atmospheric conditions. In the meantime, if you are due to jet off somewhere the best advice is to see your doctor to check if any risk factors apply to you.

Professor John Scurr is a consultant vascular surgeon at the Middlesex Hospital in London. He is an expert on travellers' thrombosis and is currently advising the WHO in relation to DVTs.

He says risk factors can include a recent operation, old age, having had a blood clot before or suffering from a condition called thrombophilia, which may occur in some women on the Pill.

The first-class passenger who died recently, Ann Price, had a blood clot 20 years ago, and was also on hormone replacement therapy, which can possibly slightly increase the risk of DVTs.

Prof Scurr says: "If somebody young and taking the Pill goes on a plane, sits still, perhaps has too much to drink and is dehydrated, then they're at greater risk of getting a blood clot. As far as we know ,it's pure immobility which can cause it on planes, so it can affect people in coaches, cars and trains as well.

"Nobody knows whether being on an aeroplane on its own causes an increased risk. If the lower pressure and oxygen were proved to be important, then being on an aeroplane could be a factor.

Prof Scurr advises people who think they could be at risk of forming a DVT on a flight to take a few sensible precautions including exercising before the flight, drinking lots of fluid, excluding alcohol, wearing compression travel stockings and moving around on the flight. But if they don't work and you are unlucky enough to form a DVT, you will know through symptoms including swelling, pain and redness in the affected area. The real danger of DVTs is that they will travel to the lungs, causing a potentially fatal pulmonary embolism.

Bob Preston, executive officer for the British Air Transport Association, stresses that the condition is caused by immobility and not air transport. "DVTs are not directly caused by flying," he insists.

"It is linked to sitting still for a long time, which is what happens on planes. They first came to light through people sitting in deckchairs in the Underground during the Blitz."

Preston points out that airlines do their best to keep passengers healthy by using in-flight information to give tips on how to avoid DVTs.

The Department of Health is also issuing travelling information, which warns that people including pregnant women and those on the pill are more at risk of forming DVTs. The precautionary advice is available both to health care professionals and the public.

But, in the future, revolutionary technology may be able to warn passengers directly that they could be in danger of forming a DVT. Sensors built into seats or clothing could alert people if their posture or lack of movement might be putting them at risk, via hand-held computers.

Anyone who is about to fly and is concerned about the risk of DVTs can get more information about the condition from Prof Scurr's website, which gets around 3,000 visits a day. Questions posted on the website, www.jscurr.com, are answered by the professor or his nurses.

Prof Scurr adds: "Anyone can fly, but some people might need to take some sensible precautions."

www.thisisthenortheast. co.uk/healthspectru