The management of normal pressure hydrocephalus (NPH) is challenging due to diagnostic uncertainties and high treatment risks. To date, there are no evidence-based treatment standards for this disorder. Our long-term goal is to improve the outcome of NPH improving our understanding of cerebrospinal fluid (CSF) hydrodynamics. The Specific Aims are to 1) determine the value of a high volume tap test, and 2) determine whether intracranial hemo/hydrodynamic variables, measured before a shunt operation, support the tuned-dynamic absorber model of intracranial pressure dynamics.