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首页> 外文会议>International Astronautical Congress >IN VIVO BONE REMODELING RATES DETERMINATION AND COMPRESSIVE STIFFNESS VARIATIONS BEFORE, DURING 60 DAYS BED REST AND TWO YEARS FOLLOW UP. A MICRO-FE-ANALYSIS FROM HR-PQCT MESUREMETS OF THE BERLINER BED REST STUDY-2
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IN VIVO BONE REMODELING RATES DETERMINATION AND COMPRESSIVE STIFFNESS VARIATIONS BEFORE, DURING 60 DAYS BED REST AND TWO YEARS FOLLOW UP. A MICRO-FE-ANALYSIS FROM HR-PQCT MESUREMETS OF THE BERLINER BED REST STUDY-2

机译：在体内重塑率测定和压缩刚度变化之前，在60天卧床休息期间和两年后跟进。来自柏林床休息研究-2的HR-PQCT模孔仪的微细胞分析

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Bed rest studies are used for simulation and study of physiological changes as observed in unloading/non-gravity environments. Among others, bone mass reduction similar as observed due to aging osteoporosis combined with bio-fluids redistribution and muscle atrophy have been analyzed. Advanced radiological methods of high resolution such as HR-pQCT (XtremeCT) allows 3D-visualizing in vivo bone remodeling processes occurring during absence/reduction of mechanical stimuli (1g) as simulated by bed rest. Induced bone micro-structure (e.g. trabecular number, cortical thickness, porosity) and density variations can be quantified. However, these parameters are average values of each sample and important information regarding bone mass distribution and within bone strength is lost. Finite element models with hexa-elements of identical size as the HR-pQCT measurements (0.082mm x 0.082mm x 0.082 mm, ca. 7E6 elements/sample) can be used for subject specific in vivo stiffness calculation. By this technique can also be quantified if bone microstructural changes represent a risk of mechanical bone collapse (fracture). Materials and Methods: In the Berlin Bed Rest Study-2,23 male subjects (20-50 YO) were maintained 60 days under restricted bed rest (6HDT) aiming to test a vibration exercise regime for maintenance of bone mass and muscle functionality at normal levels (base line measurements). For comparison a vibration resistive exercise and a control group were included. Base line HR-pQCT measurements, as well as during 3 days bed rest (BR3), BR30 and BR59, 15 days of recovery (R15), R30, R90, R180, R360, and R720 were performed. CT-scan voxels were converted into finite elements (hexa-82m edge length) for calculating in vivo compressive stiffness. Histograms of stresses distributions and anatomical regions susceptible for mechanical failure were identified and compared. Results: Vibration resistive exercises were able to maintain in the most of the subjects bone strength (von Mises stress distribution) as determined in the base line measurements. However no major differences were found in the group with vibration training alone. Without mechanical stimuli a reduction of up to 10% of bone strength was quantified. Anatomically von Mises stress concentrations, thus susceptible to fail mechanically, were observed at the center and the antero- posterior cortical bone. Conclusions: Finite element simulations from bed rest studies are an invaluable tool to determine subject specific in vivo stiffness and anatomical mechanically compromised regions which are not jet possible to be determined with any other method. Vibration exercise combined with a resistive compressive force was able to maintain bone structure and density.
机译：卧床休息研究被用于模拟和作为在卸载/非重力环境观察到的生理变化的研究。其中，所观察到的由于老化骨质疏松与生物流体再分配和肌肉萎缩合并相似的骨量减少了分析。高分辨率的诸如HR-的pQCT（XtremeCT）高级放射性方法允许三维可视化在体内骨重塑缺席/还原为模拟由卧床休息机械刺激（1G）的过程中发生的过程。诱导的骨微结构（例如骨小梁数，皮质厚度，孔隙率）和密度的变化进行定量。然而，这些参数是关于和骨质量分布和内骨强度丢失每个样本的平均值的重要信息。具有相同大小的HR-的pQCT测量（0.082毫米X0.082毫米X0.082毫米，约7E6元件/样品）的六元件的有限元模型可被用于体内刚度计算受检者特异性。通过这种技术，如果骨微观结构的变化表示机械骨崩溃（断裂）的危险，也可以定量。材料与方法：在柏林卧床研究-2,23男性受试者（20-50 YO）保持在受限制的卧床超过60天（6HDT）旨在测试振动锻炼制度在维护正常的骨量和肌肉功能水平（基线测量）。用于比较的振动抗阻力运动和对照组都包括在内。基线HR-的pQCT测量，以及在3天卧床休息（BR3），BR30和BR59，恢复15天（R15），R30，R90，R180，R360，和R720进行。 CT扫描体素被转换成有限元（六82米边长度），用于在体内压缩刚度计算。应力分布和易受机械故障的解剖区域的直方图被确定，并进行比较。结果：振动电阻练习能够在大部分受试者骨强度（von Mises应力分布）作为基线测量确定维护。但是没有单独振动训练组中发现了重大分歧。没有机械性刺激减少高达骨强度10％的定量。解剖学上的von Mises应力集中，从而易患机械失效，均在中心和后部antero-皮质骨观察。结论：从卧床休息研究有限元仿真是一个非常宝贵的工具，以确定体内的刚度和机械解剖损害区域不属于喷射可以与任何其它的方法来确定受检者特异性。振动运动具有电阻的压缩力相结合能够保持骨结构和密度。

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