A measurement system and a test sequence have been developed to determine the in vivo elastic response of brain tissue in terms of a pressure-depth ratio. This parameter appears sensitive to changes in the tissue environment that may occur due to the influence of, e.g., anesthetic agents, hyperventilation, etc., and thus may be useful in evaluating such influences. The measurements are made with the dura-arachnoid membranes intact, thus maintaining the influence of the cerebrospinal fluid compartment on the response behavior of the brain tissue that comprises the subpial region. As an integral part of the test, the procedure also serves to determine the depth or position of the subpial region and thus assures that the subsequent pressure-depth measurements invole brain tissue response. Finally, some discussion is given to relating the measured pressure-depth ratio to the classical elastic modulus. Values of the pressure-depth ratio and the corresponding elastic modulus for seven dogs are given.
✓ Because of the range of pressures associated with the intracranial system, correct interpretation of epidural intracranial pressure measurements requires an accurate means of measuring the pressure, the depth at which the pressure is measured, and the region of the system associated with that depth. A measurement system is described that provides such an accurate pressure/depth determination and maintains a uniform rate-of-insertion of the pressure transducer; the latter provision is important because of the viscoelastic behavior of the brain tissue. Use of these experimental methods to determine the pressure in three distinct intracranial regions is described, namely, in the subarachnoid and the subpial compartments and a transitional region between these two.
✓ A method for monitoring brain surface pressure through the intact dura has been designed based upon the concept of a coplanar, non-sensitive ring transducer. The transducer detects the underlying brain pressure while the stretching forces of the dural membrane are dissipated at the outer ring. The strain gauge consists of a piezo-resistive silicon-chip sensing element and a dummy element that provides temperature compensation. Cisternal cerebrospinal fluid (CSF) and brain surface pressures were monitored simultaneously in dogs under general anesthesia, both before and after increased intracranial pressure was produced experimentally. A difference was found between CSF and brain surface pressures. Possible explanations for this observation are discussed.
In an earlier study [Am. J. Physiol. 232 (Regulatory Integrative Comp. Physiol. 1): R27-R30, 1977], we defined the concept of brain elastic response in vivo as measured by a pressure-depth ratio (G0) derived from a graphic analysis of the elastic response tests. These tests have shown that brain elastic response in vivo is sensitive to changes in the intracranial system and that the response is nonlinear. In this study we identify a second parameter, G0, a second-order pressure-depth ratio that characterizes the nonlinear behavior and, along with G0, can be evaluated from a mathematical relation that models the experimental results obtained from the elastic response test. The equation is a logarithmic function relating the pressure and the subpial insertion depth. From this we obtain G0 and G0 as the slope and curvature of the response function at the subpial position. In animal experiments we correlated the changes in these parameters with those of cerebral hemodynamics during hemorrhagic and drug-induced hypotension. The calculated values of G0 and G0 are reproducible and reflect changes in cerebral blood flow and/or volume.
The elastic response behavior of brain tissue in vivo has been shown to be sensitive to the physiological environment of the brain and thus represents a useful parameter for identifying effects of controlled changes on the system. Here we describe a method for measuring brain elastic response using an epidural pressure-depth transducer and a minimum number of insertions. The method also serves to identify the nonlinear response of brain tissue.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.