Experimental brain damage from fluid pressures due to impact acceleration. 4. comparative studies with acceleration-concussion.

In order to elucidate the cause of brain damage in head injuries experiments are often designed to cause impacts to the intact skull of animals. To study the injurious significance of the contre-coup part of the impact acceleration pressure pattern we have previously applied direct loading through a parietal opening to the rabbit skull cavity. In order to evaluate the effects of the acceleration, similar impacts were delivered with greater magnitudes of such movements of the intact reinforced rabbit skull with the same equipment attached but without trephine opening. Varied and predictable acceleration, velocity and displacement of the head, and minimized skull deformation were possible with this model. Threshold levels of such impact acceleration were studied with regard to changes in respiratory and vasomotor activities ("concussive response"). Vascular permeability changes in the brain and spinal cord were studied with Ean's blue-albumin injection before the impact. Morphological observations were also made at the end of the experiments. No significant pathophysiological or morphological effects were elicited below peak acceleration of 2000 gn (duration 0.7 ms), peak velocity of 5 m/s or total dislocation of the head of 30 mm. At higher levels of impact a "concussive response" was elicited without fractures of the skull bone or significant brain lesions. Thus, in impact tests resulting in acceleration magnitudes far below those levels the signs of brain damage induced might mainly be related to the mechanical effects added--i.e. the fluid pressure loading.