Neuroscience Research Australia and Prince of Wales Clinical School, University of New South Wales, Sydney, NSW, Australia.
Philips Australia & New Zealand, Sydney, NSW, Australia.
J Physiol. 2020 Dec;598(24):5789-5805. doi: 10.1113/JP279458. Epub 2020 Oct 8.
Respiration plays a key role in the circulation of cerebrospinal fluid (CSF) around the central nervous system. During inspiration increased venous return from the cranium is believed to draw CSF rostrally. However, this mechanism does not explain why CSF has also been observed to move caudally during inspiration. We show that during inspiration decreased intrathoracic pressure draws venous blood from the cranium and lumbar spine towards the thorax. We also show that the abdominal pressure was associated with rostral CSF displacement. However, a caudal shift of cervical CSF was seen with low abdominal pressure and comparably negative intrathoracic pressures. These results suggest that the effects of epidural blood flow within the spinal canal need to be considered, as well as the cranial blood volume balance, to understand respiratory-related CSF flow. These results may prove useful for the treatment of CSF obstructive pathology and understanding the behaviour of intrathecal drug injections.
It is accepted that during inspiration, cerebrospinal fluid (CSF) flows rostrally to compensate for decreased cranial blood volume, caused by venous drainage due to negative intrathoracic pressure. However, this mechanism does not explain observations of caudal CSF displacement during inspiration. Determining the drivers of respiratory CSF flow is crucial for understanding the pathophysiology of CSF flow disorders. To quantify the influence of respiration on CSF flow, real-time phase-contrast magnetic resonance imaging (MRI) was used to record CSF and blood flow, while healthy subjects (5:5 M:F, 25-50 years) performed either a brief expiratory or inspiratory effort between breaths. Transverse images were taken perpendicular to the spinal canal in the middle of the C3 and L2 vertebrae. The same manoeuvres were then performed after a nasogastric pressure catheter was used to measure the intrathoracic and abdominal pressures. During expiratory-type manoeuvres that elevated abdominal and intrathoracic pressures, epidural blood flow into the spinal canal increased and CSF was displaced rostrally. With inspiratory manoeuvres, the negative intrathoracic pressure drew venous blood from C3 and L2 towards the thoracic spinal canal, and cervical CSF was displaced both rostrally and caudally, despite the increased venous drainage. Regression analysis showed that rostral displacement of CSF at both C3 (adjusted R = 0.53; P < 0.001) and L2 (adjusted R = 0.38; P < 0.001) were associated with the abdominal pressure. However, with low abdominal pressure and comparably negative intrathoracic pressure, cervical CSF flowed caudally. These findings suggest that changes in both the cranial and spinal pressures need to be considered to understand respiratory CSF flow.
呼吸在中枢神经系统周围的脑脊液（CSF）循环中起着关键作用。吸气时，人们认为增加的颅静脉回流会将 CSF 向前牵引。然而，这种机制并不能解释为什么在吸气时也观察到 CSF 向后移动。我们发现，吸气时胸腔内压力降低会将颅静脉和腰段脊柱的静脉血吸入胸腔。我们还发现，腹部压力与 CSF 向前移位有关。然而，当腹部压力较低且胸腔内压力相当负时，会出现颈段 CSF 的向后移位。这些结果表明，需要考虑椎管内硬脊膜下血流的影响，以及颅血容量平衡，以了解与呼吸相关的 CSF 流动。这些结果可能对治疗 CSF 阻塞性病变和了解鞘内药物注射的行为有用。
人们普遍认为，在吸气时，CSF 向前流动以补偿由于胸腔内负压导致的颅静脉引流引起的颅血容量减少。然而，这种机制并不能解释在吸气时观察到的 CSF 向后移位。确定呼吸 CSF 流动的驱动因素对于理解 CSF 流动障碍的病理生理学至关重要。为了量化呼吸对 CSF 流动的影响，我们使用实时相位对比磁共振成像（MRI）来记录 CSF 和血流，同时让健康受试者（5:5 男：女，25-50 岁）在呼吸之间进行短暂呼气或吸气努力。横向图像垂直于 C3 和 L2 椎骨的椎管拍摄。然后，在使用鼻胃管测量胸腔内和腹部压力后，进行相同的操作。在呼气型操作中，升高的腹部和胸腔内压力会增加硬脊膜下进入椎管的血流，CSF 向前移位。在吸气型操作中，胸腔内负压会将 C3 和 L2 的静脉血吸入胸腔脊髓管，尽管静脉引流增加，但颈段 CSF 也向前和向后移位。回归分析显示，C3（调整 R ²=0.53；P<0.001）和 L2（调整 R ²=0.38；P<0.001）处 CSF 向前移位与腹部压力相关。然而，在腹部压力较低且胸腔内压力相当负时，颈段 CSF 向后流动。这些发现表明，为了理解呼吸 CSF 流动，需要考虑颅压和脊髓压的变化。
