By Margaret Lee

You sit at your desk for hours, either at work or at home mugging for your exams. Are you - like passengers cramped into seats in economy flights - at risk of deep vein thrombosis?

This is a fear that student Soon Siew Ling, 17, has. She is at her desk studying for about six hours a day, sometimes more during exam time.

'I like to cross my legs when I sit down and study so I tend to get numb after a few hours. When I'm cramming for exams I lose track of time and don't really take breaks or get up to stretch my legs,' she said.

Otherwise known as DVT, deep vein thrombosis occurs when a person's blood flow to the lower limbs is impaired and he subsequently suffers a blood clot in the region. It often results in pain and swelling of the ankles, calves and feet, although these symptoms do not necessarily indicate where the blood clot is.

Although the condition itself is not life threatening, the complications of DVT, that is, a pulmonary embolism, can kill.

A pulmonary embolism is when the blood clot dislodges itself, travels to the heart and blocks the blood supply to the lungs. This in turn causes the patient to collapse.

However, vascular surgeon Chia Kok Hoong of Tan Tock Seng Hospital said that the risk of a pulmonary embolism occurring in DVT patients is relatively low.

The British Department of Health estimates that one in 2,000 people will develop DVT, while one in every 100 people who develop DVT dies.

The greatest risk of a pulmonary embolism occurring is during the acute stage of DVT, that is, within the first 24 hours of the blood clot forming.

A study conducted in 2007 by doctors from the Medical Research Institute in New Zealand suggested that office workers are at a higher risk of developing DVT.

It found that one third of the 62 patients admitted to hospital with DVT were office workers who spent hours sitting at their computer.

But both Associate Professor Chia and Dr Tan Yong Seng, a heart, vascular and lung surgeon at Mt Elizabeth Hospital, said they have not seen a case of DVT brought about by extended periods of sitting at a desk or in front of a computer.

They noted that the three main factors that are responsible for the formation of clots are thickening of the blood, diminished blood flow and vascular trauma.

This means that prolonged immobility, dehydration and an injury that affects blood flow or damages the veins are the major causes of DVT.

Those with a genetic predisposition to blood clotting are naturally at a higher risk. However, those who have lead very sedentary lives, are bedridden or have undergone major surgery are also susceptible to the condition.

Some heavily pregnant women may also be more susceptible to DVT because the venous return to the lower limb is constricted when the uterus presses on the veins in the pelvic region.

The average healthy office worker is generally not at risk of developing DVT as the environment and the daily activities of living - such as getting up to use the bathroom and going for lunch breaks - do not promote DVT unless the worker is presented with additional risk factors.

Prof Chia says: 'In order for a patient to be really exposed to the dangers of DVT, they need to remain immobile for approximately 24 hours, which usually occurs in an artificial or abnormal environment.'

He adds that it is crucial to establish the cause of DVT if it occurs in an ordinarily healthy person as it is often the symptom of larger issues, such as a tumour or genetic deficiency in proteins C and S.

It could also be a signal that the person needs to change his lifestyle, for example, to exercise more or cut down on alcohol and cigarettes.

Preventing DVT

• Don't smoke. Smoking thickens the blood as carbon monoxide from cigarette smoke posions the haemoglobin that carries oxygen from the lungs to the rest of the body.
  
  
• Don't cross your legs for prolonged periods of time.
  
  
• When flying, request for an aisle seat as this allows you more legroom. Also, try to keep moving.
  
  
• Drink plenty of water or juice when flying. Tea, coffee and alcohol act as diuretics and dehydrate the body, thus, thickening the blood.
  
  
• Wear comfortable, loose clothing as it makes you more mobile.
  
  
• Ask your doctor to recommended a pair of compression or anti-DVT stockings.
  
  
• High-risk patients should consult their doctor for preventative medication, such as injections, before long-haul flights.

This article was first published in Mind Your Body, The Straits Times on Jan 8, 2009.