Biomechanical aspects of a fluid percussion model of brain injury.

The fluid percussion model is in widespread use for the study of brain injury. However, the tissue deformation characteristics of the model have not been determined. Studies have suggested that at high levels of fluid percussion, the fluid percussion model is primarily a model of brainstem injury. It was proposed that this occurs as a direct result of the volume influx to the cranial vault at the moment of impact. This study examines the biomechanical deformation produced by the fluid percussion model. The purpose of this investigation was to describe the regional strain distribution in brain tissue at the moment of impact and to determine the effect of volume efflux produced by the percussion device. A cat skull was sectioned parasagittally and filled with an optically transparent gel. A grid pattern was painted in the midsagittal plane and was used to record the surrogate brain tissue deformation in response to fluid percussion loading. Motion of the grid pattern at low and high levels of fluid percussion loading was recorded using a high-speed camera, and a series of photographs developed from the high-speed film were analyzed to determine the intracranial strain distribution at these loading levels. The results of these studies indicated that the maximum site of strain was located in the region of the lower brainstem and that deformations were negligible in other regions of the brain. These studies provide an explanation for the pathophysiologic results obtained in a parallel series of experiments from which it was concluded that high-level fluid percussion is predominantly a model of lower brainstem injury.