Analysis of Cerebrospinal Fluid Rheology using Shear and ExtensionalTechniques

Understanding the rheological behavior of cerebrospinal fluid (CSF)will be critical in the development of head-brain system biomechanicalmodels as well as surgical and medical devices and techniques directedat alleviating intracranial pressure or altering CSF flow. CSF servesmany functions in the head-brain system including cushioning the brainagainst impact, providing nutrient transport, and clearing waste via theglymphatic system. It is derived from blood plasma and is oftenconsidered a protein free Newtonian fluid, since typical CSF proteincontent is found to be between 25-60 mg/100g. However, it has beenshown that the protein content of CSF can be different depending on thelocation (e.g. lumbar vs ventricular shunt) as well as condition of thepatient (e.g. shunt infection, hemorrhage, or obstruction) from whom ithas been extracted. In this study, we have performed a comprehensiverheological analysis of CSF specimens extracted from neurosurgicalpatients at the UCLA hospital. These specimens were tested using aconventional shear rheometer as well as a recently developed micro-extensional technique, which has been shown to be much more sensitiveto protein content of dilute solutions. Preliminary tests show weakextensional behavior consistent with the protein concentration of CSF.The results of this study have shown that CSF exhibits quantifiable non-Newtonian behavior, and that this behavior may be influenced by themedical condition of the patient. Though the non-Newtoniancontribution is relatively small, this characterization of CSF may havesignificant impacts on the development of brain models and medicaltechnologies.