engleski

Role of hydrostatic and osmotic pressures in volume regulation of cerebrospinal fluid

Introduction: It is generally accepted that extents of cerebrospinal fluid (CSF) secretion and absorption are main factors determining the volume of CSF. Thus, an increase of CSF volume and pressure are expected when CSF secretion increases or CSF absorbtion into dural venous sinuses decreases. So far the secretion and absorbtion of CSF was calculated by indirect methods such as ventriculo-cisternal perfusion with test substance and dilution of this substance in perfusate. Our new experimental model of cannulation of aqueduct of Sylvius enables direct follow up of CSF volume changes in isolated ventricles. Materials and Methods: In cats anaesthetized with chloralose an acute blockage of aquaeduct was performed by position of cannula through a small tunnel performed in cerebellar vermis. After hermetic reconstruction of occipital bone the CSF pressure was measured in both isolated ventricles and subarachnoid space (cisterna magna). In another series of experiments the outflow of CSF through canulla was measured under physiological pressure as well as during infusion of isoosmolal or hiperosmolal mock CSF into isolated ventricles. Results: During two hours after cannulation of aquaeduct no significant changes of CSF pressure were observed either in isolated ventricles or in cisterna magna. In another series of experiments no outflow of CSF through canulla was registered. During infusion of isoosmolal mock CSF in isolated ventricles the outflow from canulla equaled infusion. However, during infusion of hyperosmolal mock CSF the outflow was higher for two thirds than inflow. Conclusion: The results indicate that under normal CSF pressure there is no net formation (secretion) of CSF within ventricles. It appears that volume of CSF is regulated by hydrostatic and osmotic pressures operating between bloodstream and CSF. All this speaks against generally accepted hypothesis of secretion, unidirectional circulation and absorption of CSF.

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nije evidentirano