On the bulk motion of the cerebrospinal fluid in the spinal canal
On the bulk motion of the cerebrospinal fluid in the spinal canal
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DOI：
10.1017/jfm.2018.67
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发表时间：
2018-04-25
影响因子：
3.7
通讯作者：
Lasheras, J. C.
中科院分区：
文献类型：
--
作者：
Sanchez, A. L.;Martinez-Bazan, C.;Lasheras, J. C.
Di Chiro于1964年在《自然》杂志上发表的放射性核素扫描图像显示，注入脑室的粒子示踪剂沿椎管向下沿着迁移，同时还显示注入椎管腰椎区域的示踪剂向上流动。从那时起，许多放射学测量证实了这些观察结果，这些观察结果一直是假设的基础，即一定存在与脑脊液（CSF）深入椎管并随后将一部分返回颅顶的运输相关的主动循环机制。然而，到目前为止，还没有物理解释的机制负责建立这样一个整体再循环运动。为了研究这种再循环流的起源和特征，我们分析了脑脊液在椎管蛛网膜下腔的运动。我们的分析解释了椎管的细长几何形状、椎管内包围CSF的硬脑膜的小顺应性以及CSF局限于脊髓周围的薄环形蛛网膜下腔的事实。我们应用这个一般的配方来研究在一个简化模型的椎管组成的一个细长的兼容的圆柱形管与同轴的圆柱形夹杂物，在其远端封闭，并在其开放的入口处受到小的周期性压力脉动的流动特性。我们发现，当地的加速度和粘性力之间的平衡产生的领先顺序流组成的纯振荡运动的轴向速度的顺序为几厘米每秒和振幅单调递减沿着的长度的运河。然后，我们表明，与对流加速度相关的非线性项有助于二阶校正组成的稳定的流，产生大量的CSF的再循环运动沿着的长度的运河的特征速度比领先的顺序振荡流的两个数量级小。这种理想化的几何形状的椎管的分析结果被证明是在良好的协议，不仅在体外模型的实验测量，但也与在成人进行的放射学测量。
Radionuclide scanning images published in Nature by Di Chiro in 1964 showed a downward migration along the spinal canal of particle tracers injected in the brain ventricles while also showing an upward flow of tracers injected in the lumbar region of the canal. These observations, since then corroborated by many radiological measurements, have been the basis for the hypothesis that there must be an active circulation mechanism associated with the transport of cerebrospinal fluid (CSF) deep down into the spinal canal and subsequently returning a portion back to the cranial vault. However, to date, there has been no physical explanation for the mechanism responsible for the establishment of such a bulk recirculating motion. To investigate the origin and characteristics of this recirculating flow, we have analyzed the motion of the CSF in the subarachnoid space of the spinal canal. Our analysis accounts for the slender geometry of the spinal canal, the small compliance of the dura membrane enclosing the CSF in the canal, and the fact that the CSF is confined to a thin annular subarachnoid space surrounding the spinal cord. We apply this general formulation to study the characteristics of the flow generated in a simplified model of the spinal canal consisting of a slender compliant cylindrical pipe with a coaxial cylindrical inclusion, closed at its distal end, and subjected to small periodic pressure pulsations at its open entrance. We show that the balance between the local acceleration and viscous forces produces a leading-order flow consisting of pure oscillatory motion with axial velocities on the order of a few centimetres per second and amplitudes monotonically decreasing along the length of the canal. We then demonstrate that the nonlinear term associated with the convective acceleration contributes to a second-order correction consisting of a steady streaming that generates a bulk recirculating motion of the CSF along the length of the canal with characteristic velocities two orders of magnitude smaller than the leading-order oscillatory flow. The results of the analysis of this idealized geometry of the spinal canal are shown to be in good agreement not only with experimental measurements in an in-vitro model but also with radiological measurements conducted in human adults.