I am travelling to Thailand in May. In the past I have been found to have a duodenal ulcer and IBS, so my GP has warned me that I shouldn’t take aspirin. Is there any other preparation that I can take instead? Incidentally, my father suffered a DVT ten years ago after a long flight to Australia.

The research of Dr John Scurr, a London vascular surgeon who is also a pilot, as well as others interested in aviation medicine, has proved the dangers that flying presents for some people — and put them into perspective. Deep vein thromboses are more common after flying than is often supposed: many people who have suffered a small DVT are unaware of it. It’s a clot that starts in the deep veins of the lower limb or pelvis, and many begin in the calves. However, in fewer than half the cases could a clot be detected by clinical examination alone.

The real danger of DVTs is a pulmonary embolism. This is where part of the clot breaks away and is carried into an artery that nourishes the lung. Once the artery is blocked, the lung tissue, starved of nutrients and oxygen, dies.

Specialists agree that, although there are additional dangers associated with flying long distances or in very cramped surroundings, terms such as “economy class syndrome” are misleading. A passenger travelling in the first class cabin may also suffer a DVT, as may travellers on relatively short flights. Hours spent travelling by train or car are also not free of risk. In fact, any form of travel that leaves a passenger immobile for hours — or even, for instance, sitting all day in a deckchair on Brighton beach — increases the risk. Immobility of the lower limbs encourages deep vein thrombosis; they were diagnosed in people who slept in deckchairs in the Underground railway stations during the Blitz.

DVTs are more common in older people, the overweight, those who travel more frequently and whose flights are longer. They are a greater danger if travellers have other medical troubles, especially any malignancy — the risk associated with different cancers varies but is present even if the disease is under control.

Your irritable bowel syndrome may become more uncomfortable because the atmospheric pressure in an aircraft increases bloating.

The history of a duodenal ulcer is of great significance — any patient who has had an ulcer or chronic indigestion from inflammation could have an increased tendency to bleed with aspirin, the drug often recommended as a protection against DVT. A gut-bleed at 35,000ft would stretch the medical expertise of any cabin crew. Those with high blood pressure, who are at risk of having a stroke from a burst blood vessel, should also avoid aspirin when flying.

If you are known to be high-risk traveller — though this applies equally to those who are not aware of any risk — activity is a possible answer. When going by car or rail, walking about or stopping at regular intervals is easy, but wandering around an aircraft, once recommended by doctors, is, post 9/11, discouraged by cabin crew. So even on short flights, flexing and relaxing the muscles in the legs, thighs and the buttocks, as well as moving the ankles up and down at least every half hour, is a must. Those who are allowed to take aspirin should start ten days before the journey. Its efficacy as an anticoagulant is boosted by a couple of glasses of red wine. Travellers attending anticoagulant clinics should consult their doctor, as should those who have recently had surgery.

Dr Scurr has shown that compression stockings are not worn often enough — they can reduce DVTs dramatically. Another of his contributions to research is the discovery that a bioflavonoid, Pycnogenol, derived from the bark of a pine growing in southwest France, reduces DVTs and also the swollen feet that are suffered by many travellers.

This swelling is caused by plasma oozing into the tissues from brittle veins, especially if the atmospheric pressure is altered. Pycnogenol, also called Zinopin, like aspirin, reduces platelet stickiness that can start the process of thrombus formation. Pycnogenol is antithrombotic, antiinflammatory and reduces oedema. It is recommended for all travellers, and anyone likely to be immobile for hours. Zinopin: www.jscurr.com Topic of the week

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