The results from phase I of a group of studies by the World Health Organization (WHO) on the hazards of travel suggest that travellers who sit immobile for four hours or more, for example in a plane, train, bus or car, are doubling their risk of getting a blood clot (venous thromboembolism or VTE).
The absolute risk of developing a blood clot is still quite small however: double a very small number and you still have a relatively small number. The absolute risk of developing VTE from being seated immobile for four hours or more is about 1 in 6,000 the study concluded.
This is the main finding of Phase I of the WHO Research Into Global Hazards of Travel (WRIGHT) project, which was released today.
The VTE occurs when the blood stagnates in the veins after being seated for a long time. VTE usually leads to a deep vein thrombosis (DVT) and pulmonary embolism.
A deep vein thrombosis (DVT) is where a blood clot or thrombus occurs in a deep vein, usually in the lower part of the leg.
Symptoms of DVT include localized pain, tenderness and swelling. It is life-threatening when it happens together with thromboembolism, where part or all of the blood clot breaks off and travels to the lungs where it lodges in a blood vessel and becomes a pulmonary embolism that blocks the flow of essential blood. Symptoms of pulmonary embolism include pains in the chest and difficulty breathing.
DVT can be detected and treated, and so can VTE, but if it is not, it can be fatal.
One of the studies in the WRIGHT project looked at flying in particular. It showed that taking several flights over a short period of time also put travellers at higher risk of developing VTEs. This is because the elevated risk of a VTE from one flight stays high for about four weeks, and if more flights are made in those four weeks, the risk accumulates.
The WRIGHT report showed that other factors that can elevate a traveller’s risk of getting a VTE include:
- Being obese.
- Being very tall or very short (taller than 1.9 metres or 6 ft 3 in, or shorter than 1.6 metres or 5 ft 3 in).
- Using oral contraceptives.
- Inherited blood disorders that lead to increased clotting tendency.
The study did not investigate how to prevent DVT or VTE but experts do say that travellers should move their feet up and down at the ankle to exercise their calf muscles and get the blood circulating in their lower legs.
Also, travellers should not wear tight clothes during travel because they encourage blood stagnation.
The authors suggest that transport authorities, airlines and doctors should inform travellers about the risk of getting VTE while travelling.
They said further studies should be done to determine the most effective ways to prevent VTEs. This is the goal of Phase II of the WRIGHT project, which is awaiting further funding.
In the meantime the WHO advises passengers to consult their doctors about the risks of VTE before they travel.
The WRIGHT project was set up following the report in 2000 of a young female English traveller who died from a pulmonary embolism after a long haul flight from Australia. Later in that year, the Select Committee on Science and Technology of the United Kingdom House of Lords recommded research be done on DVT and associated risks and an expert group was convened by the WHO the following Spring, six years ago.
Phase I of the WRIGHT project was funded by the UK Government’s Department for Transport and Department of Health and the European Commission.
The purpose of Phase I was to confirm whether air travel increased the risk of VTE and if so by how much.
There were five studies altogether, conducted by researchers from the Universities of Leiden, Amsterdam, Leicester, Newcastle, Aberdeen and Lausanne. The studies were:
- A case controlled population study on the risk factors of VTE.
- Two retrospective cohort studies on employees of international organizations and Dutch commercial pilots that investigated risk of VTE due to air travel.
- Two pathophysiological studies that investigated the impact of immobility on travel-related VTE, and the influence, if any, of low oxygen and low pressure in the aircraft cabin on travel-related VTE.
Written by: Catharine Paddock
Writer: Medical News Today