High Pressure Is the Driving Force in Blast Injury
Blast injuries are caused by the explosion's blast waves—fronts of high pressure that compress the surrounding air, said Dr. Ibolja Cernak at a meeting sponsored by the Institute of Medicine.
Behind the blast wave is the blast wind, which causes a massive displacement of air that can reach hurricane proportions, said Dr. Cernak, medical director of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.
The interaction of the blast wave and blast wind in a battleground setting can cause several types of brain injury:
▸ Primary. Injury caused by the direct effect of blast pressure on the brain tissue.
▸ Secondary. Injury that occurs when the blast propels flying objects (such as shrapnel) into a person.
▸ Tertiary. Injury that occurs when the blast propels a person through the air to strike an object (similar to when someone is thrown from a car during a car accident).
▸ Quaternary. Injury caused by other effects of a blast, such as burns from thermal bombs or crush injuries caused by falling debris after a blast.
Dr. Cernak noted research findings have shown that blast injuries are part of a complex trauma as the whole body responds to a dramatic environment, she said. Blast injuries to the brain can be direct (when the force of the blast causes the brain to impact the skull or spine) or indirect (when the brain responds to the shock of impact on other parts of the body).
Soldiers in combat settings regularly are exposed to blasts. Even if they do not immediately and obviously show signs of a traumatic brain injury, repeated exposure to low-level blasts may cause brain injuries to develop over time, Dr. Cernak noted.