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Deep vein thrombosis: How long-haul flights can ruin more than your holiday

ABC News logo ABC News 19/12/2016

There's no doubt long-haul flights are a concern when it comes to deep vein thrombosis (DVT) © robertharding/REX Shutterstock There's no doubt long-haul flights are a concern when it comes to deep vein thrombosis (DVT) Holidays are almost here. If this year's holiday involves international travel then there's no avoiding a long-haul plane flight.

So this means jumping on a plane, plugging in your headphones and settling down to binge-watch hours and hours of inflight entertainment. It also means long hours sitting in the same seat and not moving around.

But have you ever wondered about the potential health issues that may arise when you spend that amount of time in a tin can at 20,000 feet?

DVT risk

Long flight times have always been the case for any travel to or from Australia. Some of these will be even longer once Qantas starts flying direct from Perth to London in 2018. (In what will be one of the longest flights in the world.)

There's no doubt long-haul flights are a concern when it comes to deep vein thrombosis (DVT), says deputy director at Baker IDI Research Institute Professor Karlheinz Peter.

Longest long-haul flights

• Auckland—Dubai: 17 hours, 25 minutes

• Dallas/Fort Worth—Sydney: 16 hours, 55 minutes

• Johannesburg—Atlanta: 16 hours, 50 minutes

• San Francisco—Singapore: 16 hours, 30 minutes

• Abu Dhabi—Los Angeles: 16 hours, 30 minutes

The longer the flight, the greater the risk. Any flight longer than four hours poses a risk, but it's those longer than 12 hours that are most problematic, Professor Peter said.

One study found your risk steps up every two hours you're in the air.

He says airlines should do more to make passengers aware of the risk.

"They should put much more emphasis on saying, 'when you fly with us, especially these long-haul flights, then you should really look at mobilising and, in between, stretching'," Professor Peter said.

DVT is a blood clot that forms in the deep veins of the leg, either in the calf or thigh. Often people don't know if they have a clot as they'll have no outward signs of it, but DVT can cause a range of complications, such as pain, inflammation, swelling and ulcers.

The real danger is if the clot dislodges, travels through your circulatory system and blocks the main artery responsible for blood supply to the lungs. This is known as pulmonary embolism. If the clot is small it can cause lung damage. A large clot can stop blood flow altogether, which can be deadly.

Scary numbers

Professor Peter said most travellers don't appreciate how frequently DVT occurs as a result of a long-haul flight.

"It's quite scary numbers. If you look at asymptomatic deep vein thrombosis [where there are no obvious signs], there are studies showing it occurs in up to 10 per cent of long-haul flights," he said.

It's true most of those people would not have any symptoms and won't develop any complications, but having one episode of DVT means you're much more likely to have it again.

"You might have small damage in the wall of the vein. So it makes it easier for the next immobilisation that you increase the risk slightly to have deep vein thrombosis ," Professor Peters said.

Of those who do develop symptoms, Professor Peter said in most cases, the airline has no idea.

"In the classic, long-term flight, you will probably have one or two patients who get out of the flight and will develop symptoms within the first two or four weeks after the flight.

"Typically for airlines it doesn't show up during the flight, it shows up after the flight and so they don't collect these figures."

But before you cancel your next overseas flight, this worst-case scenario is very unusual and there's not a lot of data around to help us understand the exact links between flying and DVT risk.

Some studies fail to find any link between DVT and long-distance travel. Others suggest flying directly increases a person's risk.

Airlines tend to hedge their bets and include some information on how to reduce DVT in the in-flight magazines, but don't really remind passengers to keep moving during the flight.

How do flights cause DVT?

Long-haul flights are linked to DVT because we spend very long periods of time sitting in exactly the same position, especially if you've had a few drinks and have unlimited movies to watch.

Blood begins to coagulate any time it pools or stays in one place. Being immobile increases the chances that blood will pool deep inside the veins in your legs and potentially clot.

Leg veins are a particular problem for clotting because the veins rely on being squeezed when you use your calf muscles to push blood back up towards your heart. But you're muscles aren't activated when you're sitting still.

This is why you're encouraged to move around on long-haul flights; to contract those leg muscles and improve blood flow.

Economy class syndrome?

There was a time when DVT was called economy class syndrome, the view being that those of us sitting squished up in economy class were more prone. But the idea that business class is a better option if you want to avoid DVT has long been discredited.

Interestingly studies have shown you're more likely to develop DVT if you sit next to a window, rather than the aisle seat.

It seems the downside to the great views and the wall to sleep against is that you're less likely to climb over fellow passengers and move around.

Who's most at risk?

Anyone can get deep vein thrombosis but the risk increases as you get older, with those over 70 most likely to get a clot.

Professor Peters said others who need to be aware of DVT when flying include:

• Those who've already had DVT or have family history of clots

• those with cancer

• women taking certain contraceptives, using hormone replacement therapy or who are pregnant

• people with conditions that cause clotting

There are also some suggestions that being obese, smoking and having varicose veins can increase your risk — but this is subject of debate.

Reduce your risk

If you're in the high-risk group or worried you might be, it's a good idea to see your GP when you're planning your trip.

They can help you work through a plan for how to reduce the odds — perhaps by wearing compression stockings or taking medication before you fly.

But Professor Peter said the following simple measures are a good idea for anyone on a long-haul flight:

• Move around every few hours

• Do regular leg exercises — ankle circles, pointing and flexing your feet, knee raises etc

• Don't knock yourself out with booze or sleeping pills

• Wear comfortable clothing that won't restrict movement

• Use footrests if you can

• Drink plenty of water (it keeps you hydrated and makes you go to the loo which gets you up and moving)

• Avoid alcohol or drinking too much coffee

It's also important to get to a doctor if you have any leg swelling, unexplained pain or shortness of breath two to four weeks after you travel on a long-haul flight.

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