Effect of Gravity on Blood Distribution and Flow in Large Vessels of Healthy Humans

Abstract

Ultrasound imaging of vessels and flow Doppler ultrasonography were used to study the hemodynamic responses of large arteries and veins to orthostasis in 230 healthy human subjects of both sexes. The arterial system was shown to respond to orthostasis by differentially reducing the blood flow capacity and velocity, especially the blood supply to the lower extremities. During one-leg upright standing, the blood flow in the arterial bed of the weight-bearing leg was redistributed in favor of antigravity calf muscles. No blood flow redistribution was observed in the vertically oriented non-weight-bearing leg. A single voluntary contraction of the triceps surae muscles caused a transient increase in the volume blood flow in the femoral vein (by 2.5- to 5.0-fold in the recumbent position of the body and by 4- to 10-fold in the upright position).