Biomechanical analysis of blast induced traumatic brain injury- a finite element modeling and validation study of blast effects on human brain

An estimated 19.5% of all U.S. troops deployed to Iraq/Afghanistan have symptoms related to blast-induced Traumatic Brain Injury (bTBI). Up to now causal mechanisms of bTBI are unknown. Previously an anatomically detailed human head finite element model (WSUHIM) was successfully utilized to predict brain injuries from blunt impact. The measurements of wave propagation patterns within an in vivo brain continue to be a significant challenge. This study focused on validating the WSUHIM against measured intracranial pressure (ICP) from blast experiments and quantifying various brain response variables from Bowen\u27s blast lung thresholds. The finite element simulations of blast wave formation, wave interactions with the head and subsequent response in the brain to blast exposure various conditions were carried out. The FE model of WSU shock tube was developed and coupled with the WSUHIM to simulate the cadaveric head subjected blast wave generated from shock tube at three different blast intensities (0.074-0.104MPa). The ICPs measured at four brain locations were used to validate the WSUHIM. Four levels of overpressure (0.21-0.61MPa) and pulse duration (1-4ms) on Bowen\u27s iso lung injury thresholds were applied to WSUHIM to quantify the resulting ICP and tissue strain. The directional effects on brain responses from same blast intensities were also compared. The model predicted ICP reasonably matched to the measured ICP in cadaver heads in terms of trend at frontal, parietal, occipital and ventricular regions. For all Bowen\u27s cases, the blast overpressure propagated through brain at various magnitudes with peak brain pressure of 0.7-1.8MPa in the cortex. The peak brain strain was 2-11% and product of strain and strain rate was 6-21 s-1 at various regions. Sideways blast produced highest coup responses in the cortex while forward blast induced high strain and strain rate in brainstem. The model results revealed that the pressure wave was directly coupled to the brain. Bowen\u27s iso-damage curves produced dissimilar levels of pressure/strain brain responses which has never been reported. The effects of being adjacent to a reflecting wall were noticeable only on the region of the brain closer to the wall