Every now and again an unexpected "young death" makes the news - a celebrity, more often than not, who died a few hours, days or weeks after a long flight. Though this has been labelled the "economy class syndrome," it affects first and business class passengers as well. It is due to a blood clot that formed in stationery legs, broke free and then blocked blood supply to a vital organ like the heart, lungs or brain.

To remain alive, blood has to flow ceaselessly through our blood vessels. The heart pumps it through the arteries, and it returns to the heart via the veins. The total volume of blood circulating in an adult is between 4.7 and 5 litres. If there is a block or a break in the vessels, the blood supply either drains away or stops. Both can result in death.

Blood remains fluid as long as there is no impediment to its flow. If there is an irregularity or break in the vessel wall, one of its components called platelets collect there. A cascading reaction involving many proteins (clotting factors) occurs and a clot forms. The clot keeps extending until anticlotting factors (also present in the blood) come into play. The clot is contained. After it has served its purpose, it is broken down and absorbed.

Clots form during injuries and fractures. These are "good" clots that prevent the body from bleeding to death. Blood clots may also form if a woman is obese or pregnant. This is due to a combination of factors like physical impediment to the free flow of blood and hormonal imbalances. An excess of estrogens aggravates clotting. If activity is suddenly decreased with prolonged bed rest owing to illnesses or paralysis, stasis in the blood vessels can cause a clot. Cancers can cause blood clots, particularly blood cancers. Smoking is an independent risk factor for clots. Elevated lipids cause "fat plaques" to form along the blood vessels. This makes their lining irregular. Sensing this, platelets aggregate there and form clots. The blood can carry these clots to different parts of the body, producing symptoms and complications. Irregular heart beats can cause clots to form in the heart and then be transmitted elsewhere.

Once a clot forms, there may be warmth, redness, swelling and pain. It may cause a stroke or a heart attack. If it lodges itself in the lungs, it can cause acute breathlessness and death. Sometimes the blood vessel gets slowly blocked by an enlarging clot. This often occurs in the arms and legs. There may be pallor, tingling numbness, reduced hair growth and thin, delicate skin.

Doppler and other imaging tests can confirm the presence of a clot. Blood tests can be done if clots are found in young people to confirm a hypercoaguable state (which happens because of a genetic defect).

Clots can be removed by surgical intervention or treated with medication in the form of injections (initially) and then tablets. Treatment often has to be lifelong. Pregnant women with hypercoaguable states can carry the baby successfully to term with appropriate anti coagulation medication.

Dr Gita Mathai is a paediatrician with a family practice at Vellore. Questions on health issues may be emailed to her at yourhealthgm@yahoo.co.in