of the body-is a genuine threat to anyone travelling on a long-haul flight.
According to a recent scientific review, the risk of DVT is about three times higher in passengers on long-distance flights (more than eight hours) than in the general population-whether they are travelling in economy or not. Those at an increased risk include people who are older (the risk starts to rise after the age of 40), overweight, pregnant, taking oral contraceptives, suffering from certain medical conditions such
as heart disease or cancer, or recovering from major surgery. In addition to other factors (see box, page 26), hereditary factors, such as having a deficiency of natural anticoagulant (anti-clotting) pro-teins, can also boost the risk (Cleve Clin J Med, 2011; 78: 111-20).
It's thought that a number of circumstances associated with flying are responsible for the associated increased risk of DVT. Dehydration, cramped seating
and prolonged immobility, for example, reduce blood circulation and increase its propensity to clot. Even short-distance air travel-or any prolonged travel by car, train or other means-can increase the chances of developing DVT (Phyto-ther Res, 2004; 18: 687-95).
Left untreated, DVT can lead to a potentially life-threatening condition called 'pulmonary embolism' (PE), where a portion
of the blood clot breaks off within the circulation, from where it can eventually cause an obstruction in one of the blood vessels of the lungs. Even in cases where PE can be prevented, the presence of an unresolved blood clot can cause permanent damage to the venous valves-which prevent the back-flow of blood in the veins-and significantly affect the quality of life.
Growing awareness of so-called 'traveller's thrombosis' has led to many people taking aspirin (a blood-thinner) before and during air travel. However, the research shows that this is not an effective preventative and comes with other risks such as bleeding, so it's generally not recommended (Cleve Clin J Med, 2011; 78: 111-20).
Happily, though, there are a number of alternative ways to reduce your risk of DVT when you travel.
Minimizing the risk
In general, it's recommended that all passengers travelling long-distance:
u exercise the legs by flexing and extending the ankles, and contracting the calf muscles at regular intervals while seated;
u take regular walks around the cabin (when permitted) for five minutes every hour on flights over four hours long;
u stay hydrated by drinking plenty of water or fruit juices;
u avoid alcohol or caffeinated beverages, which are dehydrat-ing;
u be mindful of eating too much during the flight;
u not place baggage under the seat in front as this will restrict any moving of the legs;
u avoid sleeping in a cramped position and using any type of sleeping aid; and
avoid wearing constrictive clothing around the legs or waist (Cleve Clin J Med, 2011; 78: 111-20).
In addition, if you have one or more of the known risk factors for DVT (see box, page 26), consider the following tried-and-tested solutions.
u Flight socks. Research shows that specially designed flight socks, also known as 'compress-ion stockings', can reduce the risk of DVT in low-, medium- and even high-risk travellers (Clin Appl Thromb Hemost, 2003; 9: 197-201; Angiology, 2002; 53: 635-45). They work by applying gentle pressure to the ankle in partic-ular, thus helping the blood to flow against gravity.
A review by the prestigious Cochrane Collaboration, based on nine trials involving more than 2800 long-haul travellers, revealed that flight socks can reduce the risk of symptomless DVT by 90 per cent. "Wearing stockings might reduce the incidence of this outcome from a few tens per thousand passengers, to two or three per thousand," the researchers said. There is also a large and significant reduction in leg oedema (swelling due to an abnormal buildup of water) associated with wearing flight socks, according to the study's findings.
Although different types of flight socks were used in the various trials, there didn't appear to be any significant differences in terms of their efficacy (Cochrane Database Syst Rev, 2006; 2: CD004002).
u Pycnogenol. This patented extract of maritime pine bark has been much touted as a mild
blood-thinner. In a randomized controlled trial of its effects during long-haul flights, around 200 people at moderate-to-high risk of DVT were given either 500 mg of Pycnogenol (200 mg two to three hours before their flight, 200 mg six hours after that, then 100 mg the next day) or placebo pills in an identical schedule. The results showed that there were five thrombotic events in the control group, while only non-thrombotic, localized phlebitis (inflamma-tion) was observed in the Pycnogenol group. Also, there were no unwanted side-effects.
"In conclusion, this study indicates that Pycnogenol treatment was effective in decreasing the number of thrombotic events in moderate-to-high risk subjects, during long-haul flights," the research-ers concluded (Clin Appl Thromb Hemost, 2004; 10: 373-7).
Pycnogenol has also been trialled in combination with other nutrients for DVT preven-tion. In 2003, a product called Flite Tabs was tested in 200 high-risk travellers-with posi-tive results. The supplement contained a proprietary blend of Pycnogenol and natto-kinase-an enzyme found in the Japanese fermented soybean foodstuff natto. Half the group were given Flite Tabs before a long-haul flight and half were given a placebo. It was found that, while five of the controls developed DVT, no one did in the Flite Tabs group (Angiology, 2003; 54: 531-9). Now sold under the name Veincaps 90c (Aidan Corp), it is widely available over the Internet. It's also possible to buy Pycnogenol and natto-kinase separately, either online or from healthfood shops, and take the two in combination.
Another Pycnogenol-based product called Zinopin com-bines French pine bark extract with a standardized extract of ginger, known to have anti-nausea and antiplatelet actions (see www.jsmedicalsupplies.
co.uk for more information).
In a preliminary trial of 167 travellers taking two long-haul flights within three weeks, Zinopin was reported to help protect against thrombotic events and to counteract any oedematous swelling of the lower extremities (Eur Bull Drug Res, 2005; 13: 77-81). However, a future larger-scale randomized controlled trial is needed to confirm these findings.
u AiroGym. The small inflatable exercise cushion called the AiroGym has been specifically designed to help prevent DVT on long-haul flights (see www.airogym.com).
In a clinical trial described on the website, conducted by the UCL Medical School in London, the AiroGym was found to improve blood flow in the femoral vein.
"This confirms that this device effectively activates the calf muscle pump mechanism returning blood to the heart," the study reported. However, the effect only lasts as long as the exercise period-in other words, blood flow returns to resting levels as soon as you stop using the AiroGym. Also, whether use of this device actually leads to a reduced incidence of DVT remains to be seen.
u Choose an aisle seat over a window seat. One study found that airline passengers who sit by the window have double the DVT risk of those who sit by
the aisle (Br J Haematol, 2009; 144: 425-9). This may be because passengers who sit by the window are more cramped, or
it could be that aisle-seat passengers have an easier opportunity to move about the cabin.
Factfile: Flight risks
u One long-haul flight increases the annual risk of venous thromboembolism (deep vein thrombosis or pulmonary embolism) by 12 per cent (BMJ, 2003; 327: 1072-5).
u Risk is further increased by consecutive long-haul flights and also potentially after a number of shorter flights within a short time frame (Isr Med Assoc J, 2006; 8: 859-61).
u Certain individuals have an increased risk of DVT, including those who:
v are pregnant or have recently given birth (within six weeks)
v are using oral contraceptives or hormone replacement therapy
v have certain medical conditions such as autoimmune disorders, cancer, heart disease or varicose veins
v have recently had surgery
v have suffered a stroke
v are obese
v are tall (over 190 cm or 6 foot 3 inches)
v are short (under 160 cm or 5 foot 3 inches)
v are over 70 years of age
v have a family history of DVT or thrombophilia (prone to blood clots)
v have suffered from DVT before; and
v have inherited risk factors such as the factor V Leiden mutation, which can cause blood clotting problems (Cleve Clin J Med, 2011; 78: 111-20; Isr Med Assoc J, 2006; 8: 859-61).
u If you think you may be at high risk for DVT, consult a qualified practitioner before you travel.
Factfile: Spotting the signs
Although DVT sometimes causes no symptoms whatsoever, the possible signs include:
u pain, swelling and tenderness in one of the legs (usually the calf)
u a heavy aching feeling
u warm skin in the affected area
u skin redness, particularly at the back of the legs below the knee.
If DVT progresses to pulmonary embolism, more serious symptoms can develop, including:
u breathlessness, which can come on gradually or suddenly
u chest pain
u sudden collapse.
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