Leg edema formation and venous blood flow velocity during a simulated long-haul flight.

INTRODUCTION: Long-distance traveling in a sitting position may be associated with an increased incidence for venous thromboembolism. As major contributing factors immobility and compression of leg veins are discussed. At present no studies have been performed measuring the time course of lower limb blood flow, leg volume and leg tissue thickness during a long-haul flight. MATERIALS AND METHODS: We measured limb volumes (plethysmographic method), lower leg tissue thickness and lower limb venous hemodynamics before, during and after 10 h sitting in modern aircraft chairs under normobaric hypoxia in healthy volunteers (n=12). RESULTS: Lower leg volume was already significantly increased after 4 h sitting (+109 ml) reaching its maximum after 10 h (+145 ml). These changes were accompanied by an increased body weight, total body water, extracellular water and tissue thickness of the tibia. No significant changes were measured for leg vessel cross-section diameters and maximal flow velocities in superficial femoral veins. After 10 h sitting core temperature, overall surface temperature and skin temperatures in front of the tibia were significantly increased. All parameters returned to baseline one day after sitting. CONCLUSIONS: Prolonged sitting in modern aircraft seats is associated with a remarkable fluid accumulation in the lower legs which mainly occurred during the first hours. These fluid shifts were independent of lower limb venous hemodynamics and vessel cross-sectional diameters.

Coagulation changes and edema formation during long-distance bus travel.

Long-distance travel in a cramped position by aircraft or by bus and car has been suggested to be associated with an increased risk for thromboembolic events. Recently, we demonstrated moderate activation of coagulation after a long-haul flight. At present the single contributing factors (i.e. hypoxia and low humidity on board an aircraft and prolonged sitting in an aircraft, car or bus inducing venous stasis) have not yet been investigated. Therefore we measured markers of coagulation and fibrinolysis as well as functional parameters of coagulation using activated thrombelastography in 19 healthy volunteers before, during and after a real 10-h bus journey. In addition, changes in leg volume were measured. Thrombelastography revealed moderate activation of coagulation in all travelers, which was accompanied by a significant increase in prothrombin fragment F1 + 2. Thrombin-antithrombin III complexes and D-dimer remained unchanged, and tissue-type plasminogen activator and plasminogen-activator inhibitor 1 decreased after travel. After the travel we found a significant increase in leg volume that was exclusively distributed in the calf. We conclude that beside long-haul flights also long-distance bus travel induces a certain activation of the coagulation system. Thus, it is questionable whether hypoxia is the crucial risk factor for thromboembolic events after long-haul flights.