Objective Shear waves that travel in the brain are highly nonlinear and can develop into shock waves. This newly observed phenomenon could have implications for concussion. Our objective was to determine the effect of the brain’s nonlinear shear wave propagation behaviour on laboratory acquired head impact kinematics through numerical simulations.
Design Head impact kinematics, obtained from controlled laboratory drops to cadaveric human heads, provided inputs to a one dimensional simulation of a cubically nonlinear shear wave equation solved with a piecewise parabolic method. Of the 292 drops, 125 caused significant motion about one axis. We assumed this would provide optimal conditions to create shears waves. The nonlinear and attenuation properties for the simulation were experimentally measured in fresh porcine brains with high frame-rate ultrasound.
Intervention Independent variable – Nonlinear and attenuating properties of the brain.
Outcome measures Peak Linear Tangential Acceleration (PLTA) measured at the skull was compared to the max PLTA acquired from the simulation for each of the 125 trials.
Results There were 17 cases where nonlinearity overcame attenuation and resulted in the PLTA amplifying as high as 40 times the initial PLTA at the skull.
Conclusions Our models of previously unobserved shear shock wave physics strongly suggest that nonlinearity is a first order parameter in brain kinematics and may have a fundamental influence on brain injury. Expanding these nonlinear simulations to three dimensions could better link head impact kinematics collected in the field with concussion risk and other head injuries.
Competing interests Head drop data were obtained in collaboration with Drs. Cameron “Dale” Bass and Jason F. Luck (Duke University, USA) and Dr. David B. Camarillo (Stanford University, USA)
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