A History of Blast Exposure May Affect the Transmission Properties of Cranial Bone

An individual who has sustained mild traumatic brain injury (mTBI) due to impact is more susceptible to a second concussion for a time, presumably due to the vulnerability of the injured brain tissue. This knowledge informed military guidelines regarding return to duty following blast-related TBI (bTBI). However, bone mechanics studies have shown that bone experiences hysteresis above certain strains as a result of microdamage, which suggests that blast exposure may also reduce the ability of the cranium itself to protect the brain from another blast. In the present study, the response of deer skull bone to blast wave exposure was measured. Oxy-acetylene driven laboratory scale shock tubes were used to produce realistic blast loading profiles. When a skull was exposed to peak blast pressures of about 600 kPa (measured with the sensor facing the direction of propagation of the blast wave) from a 41 mm diameter shock tube, the peak transmitted pressure gradually increased from 13.1 % to 40.2 % over five trials. This hysteresis was persistent and repeatable but was not observed with more localized loading. Future work could more specifically quantify blast thresholds at which persistent changes could be expected. Results from such work would further inform clinical decisions regarding return to activity following bTBI. The present results show that blast loading history of cranial bone should be understood and controlled in the design of related experiments. The results also underscore the need for accurate material properties and experimental validation of numerical models of the interaction of blast waves with the cranium.