Medical test takes to the skies

This week the largest ever international medical research project into the link between the formation of deep vein thrombosis and flying will be launched by Wits University and the National Health Laboratory Service. A thousand passengers flying between London and Johannesburg will take part in the study.

On Tuesday (April 8) the largest ever international medical research project into the link between the formation of deep vein thrombosis (DVT) and flying will be launched by Wits University and the National Health Laboratory Service.

The study has been made possible by the business community, in particular SAA which is the first airline in the world to become actively involved in research into this condition.

The research will be conducted by a team of medical professionals from South Africa and Britain under the leadership of Prof Barry Jacobson, head of the Wits surgical research unit.  

The study plans to conduct tests on 1 000 passengers flying from London Heathrow Airport to Johannesburg International Airport on SAA flights over the period of a month.

The study has been designed to examine all the factors relating to the formation of clots in the body during flying and to discover which factors cause people to be particularly at risk of developing DVT – commonly known as economy class syndrome. These factors include, among others, height, weight, gender, age, in-flight activity, genetic profile, and seating position.

In terms of the study, volunteers – 500 from Economy Class and 500 from Business Class – will have their ankles measured and give a blood sample. During the flight, they will be asked to fill in a form about their fluid intake and movement during the flight, and on arrival at Johannesburg International Airport, another blood sample will be taken and an ultrasound will be taken of their legs to determine if any clots have developed during the flight.

The study is aimed at providing the medical profession with the information they need to make   decisions on how to treat high-risk candidates and whether they need to prescribe preventative measures.

Once a DVT has occurred, 10% of the sufferers manifest serious long-term medical problems, while in roughly one percent of people the clot can travel to the lungs, which can prove fatal.

The spotlight was turned on the condition about two years ago again after numerous media reports about DVT sufferers threatening class action lawsuits against certain airlines for accommodating them in cramped conditions in the economy class sections, and for failing to warn them of the risk associated of flying in such conditions for long periods of time.

Sitting in cramped conditions for a long period of time has been known to cause clotting – it was first documented as a condition in World War II when people were huddling in bomb shelters.

Yet the medical profession’s knowledge of the condition relates mostly from what is known about surgical procedures – that during long periods of immobilisation such as during surgery, patients are at risk of developing clots. All current recommendations are thus based on surgical principles, and to date there has been little research that has proved that aviation does play a special role.

Last year a group of doctors published a report in the UK medical journal Lancet claiming that 10% of airline passengers suffered from venous thrombosis, which could be drastically reduced using support stockings in-flight. This article has been widely debated because the blood tests for clotting in their study subjects proved negative even though they claimed the ultrasound had detected the presence of clots.  

A more recent UK study, called the Lonflit Study, showed that the incidence of clotting in high-risk Economy Class passengers was between four and six percent. Lonflit also showed that the use of aspirin had a minimal impact, but that injections of anti-coagulant Clexane prior to embarkation, dropped the incidence of thrombosis dramatically.

An 8 million pound sterling study has been planned under the auspices of the World Health Organisation, to which a number of international airlines have pledged their support.

However, due to the financial crisis in the international aviation industry, constraints have been placed on their ability to commit financial resources to the study, placing some doubt on when this study can be initiated.

All modes of travel have risks – in France for example, train travel has been shown to be the largest cause of deep vein thrombosis. The general thinking is that the “danger” period appears to be after three or four hours of sitting – in an aircraft, train or even a car – or any other kind of sedentary period of activity.  

Aviation has its own problems because the effects of altitude have been shown to cause swelling in the legs. The cause is not conclusive, but some research has suggested that it is caused by water escaping from the blood vessels into the surrounding tissues.

It is therefore not known whether advising airline passengers to consume a lot of fluids is sound or not. There has also been some suggestion that altitude may reduce the ability of the body to breakdown clots, and again, the reason for this is not yet known.

Two years ago, Wits University   conducted a study of the condition on airline pilots and cockpit crews flying domestic flights in South Africa.  

The study was conducted to test the hypothesis about the number of people at risk, and the likelihood, based on this hypothesis, of pilots and cockpit crew developing DVT. Their research showed that not one pilot or cockpit crew member exhibited any form of clotting, and in fact, showed mild evidence of fluid dilution in their blood, which is the opposite of what might have been expected.

In light of this, it is interesting to note that the most prominent individual ever to develop DVT from flying was former US President Richard Nixon on a flight to the then Soviet Union. He developed a clot in his lung, known as a pulmonary embolism, and almost died. As a result, he was unable to testify at some of the Watergate hearings. Yet Nixon was flying in Airforce One, a luxurious specially equipped aircraft for the specific use of the US president.

There have also been many other cases of what is also known as Economy Class Thrombosis developing in passengers sitting in the more spacious Business and First Class sections of passenger aircrafts.

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