Blast Injury
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commonly held belief is that the pressure alone from an explosive blast injury is sufficient to cause brain injury in human beings. While this would intuitively seem to make sense, what many people do not realize is that there are no published, peer reviewed, prospective research studies with human subjects that have demonstrated this to be the case. The evidence to date is based on a few old single case studies, military documents that were not scientific research studies, and data from animal research.
There is no doubt that explosive blasts are associated with brain injury. However, there are many components to a blast that can cause injury to the body. First, there is the primary pressure wave injury, which is injury caused by the changes in the atmosphere caused by the explosion. The organs that are most vulnerable to this type of injury are those with air-fluid interfaces, such as the lungs, intestines, or inner ear. These tend to be hollow body parts. The most common type of injury from a primary pressure wave explosion is an eardrum rupture.
Then there are secondary blast injuries, in which the force of the explosion causes objects to fly through the air and strike someone. There is no doubt that this can cause a brain injury, since an object can fly through the air at considerable force and cause blunt trauma to the skull and its underlying contents. A tertiary injury is when the force of the explosion causes the person to be thrown into solid object. Clearly, this can also cause brain injury, if the person is thrown forwards with enough force.
One of the problems in stating that primary pressure waves causes brain injury in humans is that it is often impossible to know whether or not someone (such as a soldier) was only exposed to a primary blast injury or whether secondary or tertiary injuries also occurred. As Hurley and colleagues (2006) stated, “A still unresolved controversy is whether primary blast forces directly injure the brain” (p. 143, emphasis added). Similarly, Bochicchio and colleagues (2008) noted “...it is difficult to clearly distinguish between primary versus secondary or tertiary blast injury” (p.270). It is important to emphasize that no one denies this is possible, or even that it is likely, but caution needs to be taken before it is stated as a scientific fact in humans.
The word “humans” is emphasized because there is evidence that primary pressure waves alone can cause brain injury in animals. However, generalizing from animal studies to humans is not always possible. To begin with, the brains of mice, which is the animal group most often researched in these types of studies, are extremely small, structurally different, and not at all identical to the brains of humans. Secondly, the animal studies typically involve exposing them to blast forces at the end of a giant shock tube. While this may be something you see in an episode of a Tom and Jerry cartoon, it is not necessarily something that can be generalized to what soldiers experience during war time. To quote Hurley and colleagues, “The vulnerability of the human brain to primary blast injury is controversial and an area of active research” (p. 145).
As the committee of the Institute of Medicine (IOM) reported in December 2008, "There is a paucity of information in the scientific literature regarding the sequelae of blast injury, and there is a need for prospective, longitudinal studies to confirm reports of long-term effects of exposure to blasts." The IOM report was commissioned by the Department of Veterans Affairs and based on an analysis of 1,900 peer-reviewed studies.
MTBIFacts.com fully supports future research in this area but cautions against definitive statements on this topic until such research has been performed, replicated, and accepted by the general scientific community.
REFERENCES
Bochicchio et al. (2008). Blast injury in a civilian trauma setting is associated with a delay in diagnosis of traumatic brain injury. The American Surgeon, 74, 267-270.
Hurley et al. (2006). Blast-related traumatic brain injury: What is known? J Neuropsychiatry Clin Neurosci, 1, 141-145.
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Dr. Carone offers paid lectures on MTBI, “post concussion syndrome,” and symptom validity testing upon request. He can be contacted at info@mtbifacts.com.
