Intracranial pressure measurements and rheological behavior of the intracranial system in dogs.

Abstract

✓ A method for determining cerebrospinal fluid and surface brain pressures, based on the coplanar principle, is described. A previously developed coplanar transducer was revised so that accurate control in the rate and penetration depth during pressure measurements is now assured. In anesthetized dogs, measurements were made by two methods. In the first method, as the transducer was inserted and withdrawn at a constant rate and penetration depth, a typical pressure curve was obtained. In its ascending part, the subarachnoid and subpial compartments could be defined at two distinct inflection points. On its descending part the curve became asymmetric. In the second method of measurement, as the transducer was inserted to a fixed pressure displacement, a pressure decay curve was obtained which was interpreted as a stress relaxation phenomenon. The asymmetry of the pressure curve and the stress relaxation curve were ascribed to the viscoelastic properties of the intracranial system in vivo. These data suggest that, with our current method, one can determine intracranial pressures at the steady state and estimate some of the mechanical properties of the intracranial system.