http://press.rsna.org/timssnet/media/pressreleases/14_pr_target.cfm?ID=1915 ...Scientists previously believed that the primary source of the problem was a shift of vascular fluid toward the upper body that takes place when astronauts spend time in the microgravity of space. But researchers led by Dr. Alperin recently investigated another possible source for the problem: cerebrospinal fluid (CSF), the clear fluid that helps cushion the brain and spinal cord while circulating nutrients and removing waste materials. The CSF system is designed to accommodate significant changes in hydrostatic pressures, such as when a person rises from a lying to sitting or standing position. However, the microgravity of space presents new challenges.... Bit of a problem for longtime exposure to microgravity environments.