Validation of Davson’s equation in patients suffering from idiopathic Normal Pressure Hydrocephalus

Abstract

Introduction -The so called Davson's equation relates baseline intracranial pressure (ICP) to resistance to cerebrospinal fluid outflow (Rout), formation of cerebrospinal fluid (I f ) and sagittal sinus pressure (P SS ) There is a controversy over whether this fundamental equation is applicable in patients with normal pressure hydrocephalus (NPH). We investigated the relationship between Rout and ICP and also other compensatory, clinical and demographic parameters in NPH patients.Method -We carried out a retrospective study of 229 patients with primary NPH who had undergone constant-rate infusion studies in our hospital. Data was recorded and processed using ICM+ software. Relationships between variables were sought by calculating Pearson product correlation coefficients and p values.Results -We found a significant, albeit weak, relationship between ICP and Rout (R=0.17, p=0.0049), Rout and peakto-peak amplitude of ICP (AMP) (R=0.27, p=3.577e-05) and Rout and age (R=0.16, p=0.01306). Conclusions-The relationship found between ICP and Rout provides indirect evidence to support disturbed Cerebrospinal fluid circulation as a key factor in disturbed CSF dynamics in NPH. Weak correlation may indicate that other factors: variable Pss and formation of CSF outflow contribute heavily to linear model expressed by Davson's equation.

Cerebrospinal fluid dynamics in non-acute post-traumatic ventriculomegaly

“…Another contributing factor to the difference in Rout seen between the two groups could be the age of their populations, which differed significantly. A numerical, age-correction formula for Rout is not yet known, however there is evidence to suggest that Rout increases with age [50][51][52][53]. The significantly lower AMP in group A points towards cerebrovascular bed dysfunction [45-47, 54, 55] or decreased intracranial compliance.…”