Brain tissue elastic behavior and experimental brain compression

This study was designed to test the hypothesis that the progressive expansion of an extradural mass causes detectable changes in brain mechanical response properties, in particular the nonlinear elastic behavior, before any significant changes in intracranial cerebrospinal fluid pressure can be detected. In 10 chronically prepared and anesthetized dogs, incremental inflation (0.07 ml/s) of an extradural balloon caused 1) a progressive fall in the brain nonlinear elastic parameter (G0, mmHg/mm2), 2) nonsignificant changes in brain tissue elasticity (G0, mmHg/mm), 3) a disproportionate progressive rise in subpial tension, and 4) a progressive fall in local cerebral blood flow (H2 clearance), despite a modest decrease in cerebral perfusion pressure (extracranial). In previous brain compression experiments (Brain Res. 305: 141-143, 1984) we have shown that the compression site becomes compacted and stiffer (increased G0) and its nonlinear elastic parameter (G0) increases markedly. These earlier findings, coupled with the present observation of a loss in tissue nonlinearity distally to the compression site, are most likely the major mechanisms by which, with a rapidly expanding intracranial mass, tissue pressure gradients and brain displacement, including transtentorial herniation, develop.