Peripheral effector mechanism hypothesis of postflight cardiovascular dysfunction

Studies on the mechanisms of cardiovascular dysfunction after spaceflight a re important to illustrate the cardiovascular effect of microgravity and de velop appropriate multi-system countermeasures for future long-duration spa ceflights. Over the past 10 yr, we have systematically studied the adaptati onal changes in structure and function of both the heart and vessels, using the tail-suspension rat model to simulate microgravity effects. Our result s indicate that simulated microgravity induced atrophic changes and reduced contractility of the heart muscle, and upward- anti downward-regulation in structure, function, and innervation state of vessels in the brain and hin d body of the rat. In addition, more recent advances in relevant ground-bas ed and space-flight studies from different laboratories have also been revi ewed, Based on these studies, it has been speculated that, in addition to h ypovolemia, the microgravity-induced adaptational changes in the structure and function of the two main effectors of the cardiovascular system, i.e., the arterial smooth muscle and the cardiac muscle, might be among the most important mechanisms responsible for postflight cardiovascular dysfunction and orthostatic intolerance. In this paper we will review the available evi dence with comments.