Orthostatic intolerance is observed in astronauts after spaceflight, in patients with spinal cord injury and in the elderly. Their inability to compensate for the gravity-induced blood volume shift towards the legs in upright position can result in critical events as syncope. Normally, the muscle pump effect plays a crucial role in proper regulation of the fluid distribution. Leg muscle contraction increases venous return by collapsing deep veins while distal valves close. During muscle relaxation venous refilling is fastened as perfusion pressure is increased due to pressure shielding by the proximal valves. Furthermore, the connected superficial veins, which are less affected by muscle contraction, serve as an extra reservoir during venous refilling. Unfortunately, this complex physiological mechanism, in particular the contribution of deep and superficial veins in blood volume shift, remains poorly understood.

Therefore, the objective of this study is to characterise the muscle pump effect using a 1D pulse wave propagation model of the venous system including venous collapsibility, hydrostatic pressure and venous valves. A four-second muscle contraction has been simulated in a configuration connecting a deep to a superficial vein via four perforating veins.

Muscle contraction resulted in increased venous return and distal valve closure. Furthermore, increased perfusion was observed during relaxation and the superficial veins contributed to venous refilling.

In summary, the model can qualitatively reproduce the local muscle pump effect. Future work will focus on extending the model with regulation mechanisms and a closed loop circulation, which can ultimately result in increased insight in orthostatic intolerance.