Effects of microgravity on blood flow in the upper and lower limbs

Fluid shifts toward the upper body may cause differences in the blood flow of the upper and lower limbs under microgravity compared to that under gravity conditions. Blood flow was compared between the upper and lower limbs in a sitting position under different gravity levels generated by parabolic flight of an airplane. The blood flow of both the upper and lower limbs increased immediately after 0 G. Thereafter, the blood flow of both the upper and lower limbs returned to the normal level observed under 1 G. The blood flow of the upper limbs remained at the normal level during 0 G and after 1.5 G, whereas the blood flow of the lower limbs decreased during 0 G. The decreased blood flow of the lower limbs recovered to the normal level after 1.5 G. We concluded that decreased blood flow, under microgravity conditions, is observed in the lower limbs, but not in the upper limbs.