Experimental brain damage from fluid pressures due to impact acceleration. 1. Design of experimental procedure

The significance of the intracranial acceleration pressure pattern at impact to the intact skull in production of brain damage is discussed particularly as regards the contre-coup pressures. Sudden pressure changes within the cranial cavity of the rabbit were studied by means of a new impact acceleration model. The rabbit skull was connected with a cylinder. Impact acceleration was applied to the model with the skull contents serving as a "contre-coup end". Skull deformation was minimized by reinforcement of the skull vault. Acceleration, velocity and displacement of the system were recorded at various sites and could be predicted within wide ranges. Simultaneous recordings were also made of the pressure changes in the skull cavity and cylinder contents. By adjusting the acceleration course and by introducing a quantified air bubble 050, 100, 150 mm3) at the impact of the cylinder, it was possible to produce and vary an intracranial pressure pattern of "contre-coup type", including predictable subatmospheric transients. The mechanics of the intracranial pressure changes and displacements are discussed. The method seems to be suitable for studying the relations between brief negative-positive pressure variations (about 5 ms) of "contre-coup type" and pathological alterations similar to those reported in other head injury models and in human head trauma.