Thigh muscle pump function during ambulation.

Objective: It is generally accepted that blood flow in the superficial venous system of the lower extremity is anterograde whether the body is at rest (lying, sitting, or standing) or in motion (walking). However, it has been shown that during locomotion, anterograde blood flow in the superficial veins from the calf to the thigh was not observed. Instead, the blood flowed towards the intramuscular veins of the lower leg. The purpose of this study was to determine the pressure gradient directing the blood flow in the thigh venous network during ambulation.

Methods: Sixteen healthy volunteers (legs) were enrolled in the study. Venous pressure was measured in the great saphenous vein (GSV) at the upper and distal thigh and in the intermuscular vein of the posterior thigh during treadmill walking at 30, 45 and 60 stride cycles min^-1. The blood flow rate in the common femoral artery was measured by duplex ultrasound at rest and immediately following each exercise test.

Results: Fourteen lower extremities were included in the analysis; two were excluded due to technical failure. A pressure gradient (PG) directed from the superficial to the intermuscular vein was observed for the majority the stride cycle time. The magnitude of the PG from the superficial to the intermuscular vein was found to be considerably higher than the PG observed between knee and groin GSV levels. The GSV pressure averaged over the cycle time was found to be similar at the knee and groin levels, irrespective of walking frequency.

Conclusions: During natural ambulation, the resulting PG was directed from superficial to intermuscular veins for the majority of the stride cycle time. The thigh muscle pump functions as a flow diverter pump, redirecting blood flow from the superficial to the intramuscular venous networks via perforating veins.

Clinical relevance: This report addresses the mechanical aspects of the thigh muscle pump during human locomotion, specifically treadmill walking. The study establishes a correlation between the stride cycle and venous pressure changes within the thigh intermuscular and superficial venous network. The study demonstrated that the direction of blood flow from superficial veins is not anterograde; rather, the primary route for blood outflow from the superficial venous network at the thigh level is towards intramuscular veins through perforating veins. The aforementioned data, when considered alongside recently published data regarding calf muscle pump function, strongly suggest that the physiologic direction of blood flow in perforating veins is only from superficial to deep veins. Conversely, the occurrence of reverse flow should be regarded as pathological, even if observed in a healthy subject with so-called bi-directional perforating veins. The role of bi-directional perforating veins has been a topic of long-standing debate in the literature, with opinions divided as to whether they are a physiological or pathological phenomenon. This new data is valuable for future research on the pathophysiology of chronic venous insufficiency.