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The sitting position, after only one hour, is associated with changes in blood characteristics (increased hematocrit and concentrations of blood proteins in the legs which impacts blood coagulation).1,2,4
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Insufficient fluid intake can lead to dehydration, which impacts the viscosity of blood.4
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External compression from the seat and kinking of the popliteal vein (behind knee) have been cited as potential causes of vessel wall injury.1,3
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Additional conditions specific to air travel are:
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During air travel the cabin pressure, low humidity, and hypoxia in the cabin impact the body in such a way as to enhance venous stasis.3,4
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When a DVT or blood clot forms and does not dissolve on its own, it can travel through the bloodstream and lodge in the lungs, resulting in a serious and often fatal condition called Pulmonary Embolism (PE). The incidence of both DVT and PE has been proven to significantly increase during extended periods of travel.5,6
Industry studies show:
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18% of sudden deaths among long-distance travelers over a three-year period at Heathrow Airport were attributable to PE second only to ischemic heart disease7
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The incidence of DVT after air travel has probably been underestimated because most patients present symptoms many hours or days later3
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In 39 patients diagnosed with travel thrombosis 28% were after air travel and 72% were after a car, bus or train trip8
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400 individuals per year present with clinical symptoms of DVT after arriving in Sidney, Australia9
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50% of all cases of DVT and PE are asymptomatic (i.e., no physical indication develops)10
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The incidence of DVT in high risk travelers during extended air travel was evaluated by Dr. Belcaro, he found that 4.5% of the travelers developed DVT compared to a 0.24% incidence in those on the same flight that wore compression socks5
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The mass of accumulated literature over the last 40 years, including the more recent large series, makes the likelihood of such an association (between travel and DVT formation) so strong as to be virtually irrefutable11
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