Changes In Compliance Of Femoral Vein After Simulated Weightlessness In Rabbits With Histomorphology Correlation

Orthostatic intolerance is one main problem of cardiovascular deconditioning after spaceflight weightlessness. Reduced Orthostatic tolerance poses serious hazards with crewmembers during re-entry and lead to failure of space-flight mission. Further more with the development of aerospace technique, the cosmonaut would experience long time weightlessness state land on other celestial body. It is more urgent and important to conquer and reduce the threaten from Orthostatic intolerance to the cosmonaut. The studies on the field have been paid more attention to by the scientists of many countries. The basic mechanism of post-flight Orthostatic intolerance has not been fully elucidated up to now. Today, we have realized that single factor cannot explain the cause of Orthostatic intolerance. The reasons involved the changes of venous compliance, functional status of heart, lose of blood volume or body fluid, changes of endocrinous system , altered responsiveness of baroreflex and so on. Commonly deemed that when the venous compliance of lower limbs increased and then there is more blood retention in lower limbs veins, bloodvolume back to heart reduces during body up-stand after weightlessness or weightlessness simulated, the cardiac output and blood pressure of artery are descend, which promote the occurrence of orthostatic tolerance. However, the studies of effect on venous compliance from weightlessness or weightlessness simulated are variance at present. Majority researcher reckon that the venous compliance of lower limbs is increased after weightlessness or weightlessness simulated. Watenpaugh DE found the venous compliance of lower limbs just increased at the first week after spaceflight using the method of vein blocked. Bonde etal discovered during the test of 20-D bed rest that the venous compliance of lower limbs short-lived increased merely on the third day and cameback to the level of pro-bedrest on the fifth day.(vein blocked method). Melchior et al also found that the venous compliance of lower limbs had not changed during 13- D bed-rest test with blocking vein method. By this token the changes of venous compliance and its effect factors cannot be definituded. We think that this kind of difference comes from disunity in the measure method of venous compliance. The change rate of low-limbs volume is adopted frequently to show the change of venous compliance in Bed-rest test and flight test. There are multifactors determine the changes of low limbs volume, not only the venous system, but also the muscle and body fluid. Therefore, the change rate of low-limbs volume cannot reflect the changes of venous compliance actually. We adopt the rabbit models with Head-down Tilt(-20?) to simulate the changes in men during spaceflight and measure the low limbs vein and observe the structure of venous wall directly in our experiment, so that we get rid of the infection from disadvantage factors and find out the rules and causes of change in venous compliance.In this study, we divided 24 New Zealand rabbits into 3 groups namely: control group; HDT-10d; HDT-21d, with 8 rabbits in each group. Utilizing measure technique of P-V relationship curves of femoral vein in Vivo, we measured the venous compliance of the rabbit femoral vein from all the groups. We measured the longitudinal and circumferential stress-strain relationship curves of femoral vein in vitro, to study effects on venous compliance after weightlessness simulated. We also observed the changes of the microstructure and ultra-structure of the femoral vein, using both the optic and electronic microscopes.The main results were as follows:1. The Pressure-Volume relationship curves of femoral vein of the rabbits shifted after simulated weightlessness and that of HDT-21d shifted more obviously than HDT-lOd.Contrast to control, the femoral vein P-V relationship curves of HDT groupsshifted to larger volume change ratio, especially in HDT-21d groups. B) and 82 inquadratic equations of HDT-21d group were significantly higher th...