BIOMECHANICS OF TRAUMATIC COMA IN THE PRIMATE (HEAD INJURY)

Non-penetrating head injuries are a major problem facing society today, accounting for billions of dollars of hospital costs and lost income each year 68 . Recognizing that each type of head injury is associated with a unique set of loading conditions and pathology pattern, this dissertation focussed on one particularly serious head injury, traumatic coma, also known as diffuse axonal injury (DAI). DAI occurs most frequently as a result of lateral, rotational motions of the head, and can be produced in the absence of impact. Integration of physical, analytical and animal models for DAI with clinical and isolated tissue data shed light on the complex relationship between head motion and prolonged unconsciousness. Simple physical models of the head were used to investigate the influence of head size, brain shape, brain/skull adhesion and applied load on tissue injury (as indicated by intracranial deformation). Skull physical models for baboon and man were developed to determine the influence of the falx cerebri on brain motion, and as an empirical method to scale applied loads to man. Deformation patterns of models accelerated at levels known to produce DAI were compared to pathology data. Large deformations occurred in regions at high risk to injury. Maximum strain levels in such regions increased linearly with peak rotational accelerations ((\u27)(theta)(,p)). A continuum analytical model developed to describe DAI consisted of a rigid, right-circular cylindrical shell filled with a Kelvin-Voigt viscoelastic material subjected to a sudden, distributed, axisymmetric, rotational load. The strain response for brain was examined as brain size and applied load magnitude, duration and waveshape were varied independently. Strain increased linearly with increasing (\u27)(theta)(,p) and exponentially with increasing brain size (where the exponent, n, was frequency-dependent). Animal data for DAI scaled to man using the physical and analytical models generated in this work led to the development of the first threshold for DAI in man. The modelling methods put forth in this work set the stage for similar investigations of other types of diffuse head injury, leading to the development of a family of injury-specific thresholds for man