Meaningful concepts of head injury criteria
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Current head injury tolerance parameters or criteria used for regulation involve linear acceleration levels or their histories for the entire cranium. Other proposed criteria pertain to angular acceleration, or a mean strain; a viscous criterion has been proposed for soft tissue. Such prescriptions are unable to differentiate between various regions of the head. Also, except for strain, the other parameters do not directly produce trauma and can thus at best only be indirectly related to trauma. It is important to devise a methodology that will permit the stipulation of loading limits of individual tissue using accepted engineering failure parameters for physical disruption and, concomitantly, a proportionately lower limit for physiological dysfunction. This contribution describes such a procedure based on the principles of continuum mechanics and the knowledge of material properties. It represents a further development of the suggestion of the author 23 years ago to analyze head response to impact by means of these analytical tools. An example of the response to impact of a viscoelastic tube which could be extended to model the loading of a cerebral vessel due to a head collision is indicated.