Abstract
Venous stasis caused by combined effects of immobility and an increased gravitational pressure gradient between the heart and lower limbs is an important risk factor for deep venous thrombosis (DVT) in long-haul air travel. Accordingly, the effects of sitting posture on lower limb hemodynamics have been a matter of great interest, and it was found that the popliteal venous flow velocity was decreased to 20% and the cross-sectional area was increased to 500% by posture change from prone to sitting, while the flow volume (flow velocity × cross-sectional area) was not altered. Devices and/or maneuver that increase the venous flow velocity are thought to be effective for reducing venous stasis. An ottoman-type (business class) seat significantly improved the flow velocity and cross-sectional area of the popliteal vein. Muscle contraction induced by neuromuscular electrical stimulation of the gastrocnemius (NMES) also improved the venous flow velocity; however the cross-sectional area was not affected by NMES. Furthermore, combination of graduated compression stocking and NMES significantly improved lower limbs hemodynamics of bed-ridden patients; the effect was comparable with intermittent pneumatic compression, which is commonly used as a prophylaxis of DVT. These results indicate that immobility and an increased gravitational pressure gradient are the major factors for lower limbs venous stasis; upgrade a seat to a business class and/or muscle contraction are effective for improving venous stasis. [J Physiol Sci. 2008;58 Suppl:S39]
