Vascular adaptation to microgravity: what have we learned?

Findings from recent bed rest and spaceflight human studies have indicated that the inability to adequately elevate the peripheral resistance and the altered autoregulation of cerebral vasculature are important factors in pos tflight orthostatic intolerance. Animal studies with rat model have reveale d that simulated microgravity may induce upward and downward regulations in the structure, function, and innervation of the cerebral and hindquarter v essels. These findings substantiate in general the hypothesis that microgra vity-induced redistribution of transmural pressures and flows across and wi thin the arterial vasculature may well initiate differential adaptations of vessels in different anatomic regions. Understanding of the mechanisms inv olved in vascular adaptation to microgravity is also important for the deve lopment of multisystem countermeasures. However, future studies will be req uired to further ascertain the peripheral effector mechanism of postflight cardiovascular dysfunction.