Critical Limitations on Significant Factors in Head Injury Research

The response of the head to blunt impact was investigated using anesthetized live and repressurized- and unrepressurized-postmortem Rhesus. The stationary test subject was struck on the occipital by a 10 kg guided moving impactor. The impactor striking surface was fitted with padding to vary the contact force-time characteristics. A nine-accelerometer system, rigidly affixed to the skull, measured head motion. Transducers placed at specific points below the skull recorded epidural pressure. The repressurization of postmortem subjects included repressurization of both the vascular and cerebrospinal systems. The results of the tests demonstrate that: 1) Head impact and injury response are complex phenomena and require careful attention to the experimental techniques used to obtain the impact data as well as the interpretation of the results; 2) A set of initial conditions has been found such that the repressurized-postmortem Rhesus was more similar in head impact response to the anesthetized Rhesus than was the unrepressurized-postmortem Rhesus (in terms of the transfer function relationships between tangential acceleration and epidural pressure; 3) In terms of subarachnoid hemorrhage in the medulla-pons area associated with skull fracture, the repressurized-postmortem and anesthetized Rhesus were similar in injury response; 4) The initial position of the head-neck system was a critical factor associated with the brain-cerebrospinal fluid system's response to head impact; 5) The thermodynamic response (fluid vaporization) of the head-brain system was an important consideration when the impact produced significant tension; and 6) No relationships could be found between injury and negative pressures equal to one atmosphere.