Alfonso Schettini

Brain tissue elasticity and CSF elastance.

In the analysis of the pressure-volume relationship of the intracranial system, the concept of brain elastance, sometimes called tissue elastance or CSF elastance, is often used. It is generally designated as Ecsf and is calculated as the slope of the pressure-volume curve of the system. Variations in Ecsf are related to, for example, changes in the buffering capacity of the system which, however, could be influenced by the cerebral vascular volume, compressibility of the meningeal membranes, and compressibility of the subpial brain tissue. Our interest is in isolating the effect of controlled changes in the intracranial system with changes in the subpial tissue only. Here we discuss the measurement of brain tissue elasticity and describe two experimental conditions in which simultaneous measurements showed distinct differences between the behaviour of the system CSF elastance and brain tissue elastic behaviour.

Brain Elastic Behavior and CSF Dynamics in Cold Induced Edema

In a recent study we have characterized the brain instantaneous elastic response in terms of two elastic parameters: a tangent pressure-depth ratio (GO) in mmHg/mm, which is a direct measure of brain tissue elasticity (in vivo, in situ), and a curvature pressure depth ratio (GO) in mmHg/mm2, which is a quantitative measure of the nonlinearity of the elastic response (Walsh and Schettini, 1984). In the same study we showed that these elastic parameters are sensitive to changes in the physiological milieu of the brain, and may independently vary, depending upon the experimental conditions.

Brain Elastic Behavior and CSF Dynamics During Progressive Epidural Balloon Expansion

The progressive expansion of an extradural balloon causes nearly simultaneous changes in CSF dynamics, cerebral hemodynamics and brain tissue mechanical response properties, and in a complex manner (cf. Miller et al. 1973). These phenomena are difficult to predict from changes in CSF dynamics or cerebral hemodynamics until the level of mass expansion is well underway.

Brain elastic behavior in experimental brain compression: influence of steroid therapy

In chronically prepared dogs we studied the influence of large doses of steroids on experimentally increased brain stiffness. The latter was quantified by measuring brain elastic response, in terms of the (instantaneous) initial tangent, Go (mm Hg/mm). After epidurally induced brain compression (45 min), Go increased and remained elevated in spite of steroid therapy. The data suggest that steroids are ineffective in congestive hyperemia consequent to ischemic compression.

Simultaneous Pressure-Depth Measurements of the Intracranial System Made Epidurally

We have focused our efforts on the accurate, simultaneous measurement of intracranial pressure and the position or depth at which the pressure is measured in our studies. There are, essentially, two principal reasons for this. The first is that, due to the range of pressures within the intracranial system (CSF, surface brain, brain tissue), a particular pressure measurement must be identified with a position (depth) within the system. Then second, the increment of change in pressure associated with an increment of change in insertion depth is a measure of the mechanical response properties of the regions of the system, thus both must be measured.