Having just returned to Phuket from jet-setting around the Southern Hemisphere, spending long periods of time cramped in economy class seats I began thinking about economy class syndrome, known by the medical name deep vein thrombosis (DVT).

Anyone can get economy class syndrome--you do not need to be in economy class at all. People in business and first class have developed it since it's related to low cabin pressure, low humidity and dehydration. Relative humidity is 20-25% in the Arabian Desert, while optimum comfort is around 50% humidity. In-flight cabin humidities gradually fall on long-distance flights. In many cases they can be as low as 1%. That's pretty dry, and it is also the reason why people do not urinate much on a long flight unless they drink plenty of fluids

DVT has many contributors: low humidity, dehydration, low cabin pressure coupled with thickening of the blood and constriction of the veins from dehydration, a lower heart rate, and pooling blood in your legs because of gravity and lack of exercise. You can also get DVT from prolonged train or car travel, and it's more common than initially thought.

London's Heathrow airport reports one passenger death a month from DVT. In Australia, a law firm has filed one thousand DVT claims against 6 airlines in one year. Records from Tokyo's Narita airport show that, on average, 100-150 passengers are treated for DVT immediately upon arrival each year, of which 3-5% die. Even former United States Vice-President Dan Quayle nearly died from DVT during a 1994 flight.

DVT, or blood clots, form in the deep veins of the legs, usually between the ankle and upper calf. They can develop in only a few hours. Problems really happen when a clot breaks off, usually as the plane descends or when it decompresses. The clot may travel through the bloodstream and obstruct a vessel in the lungs, restricting blood flow. This condition is called pulmonary embolism, and it seriously damages lung tissues and causes poor lung function, which can be fatal. The time taken for the clot to travel from the legs to the lungs could be days, even weeks. Taking this time frame into account, researchers believe that even more people die from DVT than current statistics show.
If you're going to be in a cramped-leg position for several hours, you are at risk. The risk increases if you are obese or tall. Smokers and anyone with a history of leg clots or recent leg or pelvic surgery are also more prone to developing DVT, as are the elderly. If you have varicose veins or a history of venous problems, the chances of developing a DVT escalate.

Planning to travel and your legs are going to be cramped? Exercise. Those funny cartoons shown with a little man or an air hostess stretching their legs will get you started. Better still, get up out of your seat and walk around for a few minutes every hour. When flying, drink lots of liquids to avoid dehydration, which causes the blood to thicken and the vessels to constrict. Avoid alcohol and coffee, as they contribute to dehydration.

You can also take an aspirin before the flight and every 6 hours during. Or, if you have considerable risk factors, discuss DVT with your doctor, who may give you a shot of Heparin before the flight. Heparin is an anticoagulant that stops the blood from clotting.

Researchers also recommend wearing compression stockings, particularly for those at risk. These garments help put pressure on the leg muscles and assist in retuning blood flow to the heart. They have been shown to significantly minimize the risk.

Usually, the development of DVT will not be obvious. There may be pain and warmth in the lower legs or a prickly sensation. Swelling of the feet or legs may occur, but this happens anyway to most people on long flights who are not mobile. Swelling of the legs, feet and ankles can be a normal response to humidity, dehydration and long period of inactivity. If you develop shortness of breath during or up to a week after a flight, this could be an indication that a clot has moved to the lungs and a pulmonary embolism has developed. If shortness of breath occurs, seek emergency medical assistance without delay.