Prolonged sitting on transcontinental airline flights, prolonged car rides subject travelers to an increased risk of clot formation in the legs called "deep vein thrombosis" or DVT. During these prolonged periods of inactivity, dehydration, and pressure against the back of the legs may result in stagnant blood flow - which predisposes the traveler to the development of DVTs. Factors that may increase the risk for DVT may include older age, recent prolonged bed rest, obesity, smoking, cancer, pregnancy (particularly third trimester), recent surgery, history of phlebitis or previous DVT, recent serious illness, abnormal blood clotting capability (coagulopathy).
It is unclear how best to minimize DVT formation during prolonged flights. Some suggestions include frequent walks in the aisles, perform isometric exercises while seated, wear fitted support hose, avoid excessive alcohol intake, and maintain adequate hydration.
Talk with your primary care physician for more information about deep vein thrombosis or, if necessary, for a referral to a vascular surgeon.