An interpretation of pressure/volume interactions in the craniospinal axis

Abstract

A method is presented to help explain the genesis of cerebrospinal fluid (CSF) pressure changes associated with a variety of alterations within the craniospinal system. Translation of the x-axis is used to convert the usual plot of CSF pressure vs. change in CSF volume (CSF P/ΔV curve) to a plot of CSF pressure vs. total CSF volume (the CSF P/V curve). This translation permits analysis of craniospinal pressure/volume dynamics in terms of the factors that change CSF equilibrium pressure (Peq) or CSF equilibrium volume (Veq) or that alter the shape of the CSF P/V curve. Changes in Peq are produced only by changes in the net CSF flow/pressure relationship. The shape of the CSF P/V curve changes only in response to alterations in mechanical properties of craniospinal tissues. Veq is altered either by changes in the CSF net flow/pressure curve or by variation in mechanical properties of the tissues around the CSF space. Only CSF volume changes alter CSF pressure by movement of a point along a single P/V curve. Volume changes in all other craniospinal compartments alter CSF pressure by changing Peq, by changing Veq, or by changing the shape of the CSF P/V curve. Depending on how tissue mechanical properties are changed, on how other mechanical factors in the craniospinal axis are altered, and on how the net CSF flow/pressure function has been changed, a perturbation of the craniospinal system may selectively alter Peq, Veq, or the shape of the CSF P/V curve. After a perturbation of the craniospinal system, total CSF volume is related to a new CSF P/V curve to generate a new level of CSF pressure. If changes in the net CSF flow/pressure curve or in tissues around the CSF space occur slowly, CSF pressure and volume may not be significantly different from Peq and Veq, whereas if these changes occur rapidly CSF pressure and volume may be markedly different from Peq and Veq. (Neurosurgery, 6: 453-462, 1980)