中文摘要：

为进一步阐明短期失重下血管的适应性改变及其重力性对抗措施的机理，本文对3d模拟失重组（SUS）、对抗措施组（STD，每日恢复正常站立体位1h模拟-Gx重力）及对照组（CON）大鼠大脑中动脉和肠系膜第三级小动脉的被动和主动生物力学特性进行了分析。所研究的生物力学参数包括：被动血管的表观刚度（β）、被动和主动血管的周向应力（σθ）-应变（εθ）关系及其增量弹性模量（Einc，p）,和平滑肌收缩活动所致的激活增量弹性模量（Einc,a）。主动血管生物力学特性分析结果显示，肌源性紧张度的调节对失重下血管的适应具有重要意义：（1）SUS组肠系膜第三级小动脉的主动σθ-εθ曲线与其被动态曲线基本一致，表明通过肌紧张度调节使仉恢复正常的功能基本丧失；但每日1h的-Gx重力暴露则可完全防止此功能减退；（2）SUS组大脑中动脉的主动σθ-εθ曲线较其被动曲线明显左移，不同压力εθ始终相对稳定，σθ也趋于正常；且每日短时-Gx重力不能防止这种功能亢进。另一方面，对被动血管生物力学特性的分析则提示，不同血管的间质成分可能有不同重塑（remodeling）变化，如失重暴露时间进一步延长，将可能观察到有显著意义的重要变化。总之，本文血管生物力学特性分析对阐明失重环境下血管适应机理及其重力性对抗措施具有重要意义。

英文摘要：

The aim of the present study was to further elucidate the mechanisms of vascular adaptation to microgravity and its gravitybased countermeasure by a biomechanical approach. Active （the dissected vessel segment was superfused with PPS） and passive （while it was superfused with Ca^2＋-free PPS） biomechanical properties of mesenteric third-order small arteries and middle cerebral arteries isolated from 3-day simulated microgravity （SUS）, countermeasure （STD, daily 1 h of -Gxgravitation）, and control （CON） groups of rats were studied. The following mechanical parameters were calculated： the overall stiffness parameter of passive vessels （β）, circum- ferential stress （σθ）-strain （εθ） relationship, and pressure-dependent incremental elastic modulus （Einc.p） of both active and passive vessels, and vascular smooth muscle （VSM） activity-dependent incremental modulus （Einc.a）. Results from the analysis of active biomechanical properties revealed the contribution of vascular smooth muscle （VSM） tone during the early adaptation to microgravity： （1） For mesenteric small arteries, active circumferential σθ-εθ curve of SUS group was comparable with that of the passive vessels, indicating that the function of VSM to restore the normal stress distribution is compromised; however, this mal-adaptation was fully prevented by the countermeasure of daily 1 h of -Gx gravitation; （2） For the middle cerebral arteries, active circumferential σθ-εθ relation of SUS group was shifted to the left side of the passive curve and εθ was kept at a nearly constant level with the corresponding σθ being at its normal range; furthermore, the enhanced myogenic tone responsiveness was not prevented by daily short-duration -Gx. Analysis of the passive biomechanical properties has suggested remodeling changes in matrix components of different types of vessels, which might be significant if the exposure duration was further prolonged. In brief, studies of vascular biomechanics ar