Low-level blasts raise intracranial pressure and impair cognitive function in rats

Brain injury after high-level blast has been established both clinically and experimentally. Less is known about the effects on the brain of exposure to low to moderate blast levels, such as those encountered by military personnel during the firing of weapons. This study investigates if exposure to occupational levels of low-level blasts affect intracranial pressure and cognitive performance. Rats were exposed to blast overpressure in a shock tube at peak levels of 10, 30, and 60 kPa. Intracranial pressure (ICP) was measured after 0.5, 3, 6, and 10 h and 1, 2, 3, 5, and 7 days. We found two features of the response: a dose-dependent rise in ICP in rats exposed to blast, and an increasing time delay in elevation with decreasing intensity of exposure. The ICP increased in a dose-dependent fashion, up to 15.7 mm Hg after exposure to a 60-kPa blast from a control level of 6 mm Hg. While the initial elevation took place within 30 min after exposure to 60 kPa, it did not appear until after 2 and 6 h for 30 and 10 kPa, respectively. In all cases, the ICP returned to control levels after 7 days. The cognitive function of the blast-exposed rats was assessed with the Morris water maze. After exposure to 10 or 30 kPa and re-testing 2 days later, the latency was increased by over 100%. The results show that exposure of rats to blast levels as low as 10 kPa affects both ICP and cognitive function. Though species differences do not allow direct extrapolation to humans, these findings do pose the question as to whether the thresholds for brain injury might be lower than those of other organs used to set training standards for blast exposure.